Physical Modeling of Subgouge Deformations in Sand · Physical Modeling of Subgouge Deformations in...

Physical Modeling of Subgouge

Deformations in Sand

by

©Wei Yang

St. John's, Newfoundland, Canada

B. Eng., Harbin institute of technology, China (2005)

A thesi ubmitted to the

School of graduate studies

In partial fulfillment of the

Requirements for the degree of

Master of engineering

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

December 2009

ABSTRACT

A series of 7 tests of PIRAM (Pipeline Ice Risk Assessment and Mitigation) tests were

carried out to simulate the progress of a gouging ice keel by centrifuge modeling. This

thesis focuses on the subgouge deformations of the ice gouging process. The

relationships between gouge depth, frontal benn, force, pressure, subgouge deformation

and vertical extent of subgouge defonnation are discussed in the thesis. The PIRAM tests

were compared with the results of a similar series of previously conducted tests, and

previous tests. Significance of the frontal benn height, gouge depth, gouge rate are also

discussed.

The experimental program consisted of towing a model ice keel across a model testbed at

a set gouge depth under various centrifuge acceleration. The test setup consisted of an

aluminum half width ice keel model mounted on a gantry situated on top of the

containment box given the centerline of the model was replaced by a viewing window to

visualize the subgouge deformation accumulation. The model tests were conducted using

saturated fine sand simulating seabed. Two tests were conducted with shallow gouge

depths for comparison with previous Delft Hydraulics flume medium scale gouge tests to

evaluate the applicability of centrifuge modeling. Three tests were conducted at a fast

gouge rate since most of the previous work were conducted at a relatively slow rate. A

large amount of data regarding ice keel gouge in sand was acquired from the

experimental program the analysis of which described here in.

II

---------------------------------------------------------------------------------------------

The combined depth of gouge depth and frontal betm height has a significant effect on

the force and subgouge defonnation. The force per unit width increases as the gouge

depth increases. The vertical to lateral gouge force ratio seems to be independent of the

aspect ratio which is gouge width divide gouge depth or attack angle. The kappa value is

the frontal bem height normalized by gouge depth is linear with the aspect ratio. The

kappa value has a significant effect on gouge force and subgouge defonnation. Particle

image velocimetry (PlY) technique was successfully used to track the evolution of

subgouge deformation in all 7 tests. The maximum horizontal subgouge displacement

occurred at the base of the keel and decreased with depth. The associated maximum

gouge forces are a function of the keel attack angle and the gouge geometry. In

comparison with previous tests, the vertical extent of subgouge deformation (SGD) was a

function of combined depth and the soil state, but independent of the attack angle. The

SGD are influenced by the attack angle and the soil state. Faster gouge rates may result in

larger gouge forces by a factor of 2 to 3 and smaller horizontal subgouge def01mations

but similar vertical extent.

III

TABLE OF CONTENTS

INTRODUCTION AND LITERATURE REVIEW ....... ............ ........ ...... .. ............... 1

1.1 Introduction .... ................................................... ... ...... .................. ............. ... ...... .. I

1.2 Gouge Geometry ..... ....... ..... .. .... .... .. .. ..... .............................................................. 2

1.3 Studies oflce Gouge ...................... ....... ........ .................... .... ....... ........... ............. 4

1.4 Themical and Numerical Studies ............ ..... ............. ...... .. .... .. ........................ .. . I 0

1.4.1 Ice Gouge Life Cycle ............................. ....................... ..... ..... ............ ..... . 10

1.4.2 Ice Gouge Parameters with Pipeline Design ......................................... .... 11

1.4.3 Pipeline Trench Depth ...... ............ ......... .. .. ........ .... ..... ....... .... ..... .... .. ..... ... 12

1.5 Research Objective and Outline ................... ... ..... ... .... ... ................. ................ .. . 14

2 CENTRIFUGE MODELING ..... ... .. ............. .. .. ....... .... ........................................... .. 16

2. 1 Introduction ................................. ........... ... ........... .. ........... ...... ... ...... ... ...... .... ... .. 16

2.2 Centrifuge Modeling Principle ........................................................ .... ... ........... 17

2.3 Scaling Law for Modeling .. ... .... ... .... ..... ... ...... ........ .. ......................... ........ ........ 18

3 EXPERIMENT EQUIPMENT AND PRINCIPLES ... ... ..... .... ..... ..... .. ............... ... ... 23

3.1 Centrifuge .... .............. .. .... .. ............................. ... .. .. ........ ........ .. .. ... .... ... .... .. .. ...... 23

3.2 Strongbox ..... ........................................................................... .................. .. ....... 25

3.3 Model Ice Keel ................................................. ................. ... .................... ... ....... 27

3.4 Actuator. ............. ..... .... .... .... ..... ...................... ..... .................... .... ...... ........... ..... . 28

3.5 Data Aquisition System .. .............. ..... .......... ..... .............................................. ... 29

4 EXPERIMENT PROGRAM AND TECHNIQUES ........... .. .... .................. .. ............ 31

4.1 Introduction ... ..... .... .......... ... ........ .... .... ............. .... .... ... ...... .......... ... ..... .... .. .... ..... 31

4.2 Sand Description .............. ........... .... ................ .............. ... .................................. 31

4.3 Testing Progran1 ............................... ........ ....... ... ...... ....................................... .. . 32

4.4 Preparation of Soil Model ... ..... ... ... .. ... ... ... .. .... .. ..... .. ......... .... ........ ...... ............... 32

4 .5 Modellnstrumentaion and Data Acquisition ... .. ............................................ .... 35

4.6 Centrifuge Testing Procedure .. .. ... .... ............ ............... ...................................... 38

4.7 Particle Image Velocimetry .................................................. .......................... ... 38

5 EXPERIMENTAL RESULTS ................................................. ......................... ..... ... 42

5.1 Introduction ............................................................................................. .. ......... 42

5.2 Experimental Load Data Analysis .................... .... ...... ... .. ..... ....... ........ .... ...... .... 43

5.3 Subgouge Deformation ..... .. ....................... ...... .. ............................. ................... 53

5.4 Gouge Form and Mound .................. .. .. ...... ..... .... ..... ... ......... .. .. ... .. .... ....... ......... . 69

6 ANALYSIS ...... ... ..... .. .... .... .... .. .. ............... ..... ................. ................. .......... ......... .... .. 76

IV

6.1 Introduction ......... .. ..... .. ..... ..... ... ............... ................ ......... ......... ... ... ............ ... .. . 76

6.2 Vertical Settlement during Centrifuge Test ... ... .... .... ........ .... ...... ...... ....... .......... 77

6.3 Frontal Ben11 ............................... .... ... .. .......... ... ....... .. .......... ... .... .. ...... .. .. ...... ..... 78

6.4 Bearing Pres ure .. .... ................... ..... ...... .......... .......... ........... .. ..... ...................... 81

6.5 Gouge Force Variation ........... ......... ... .... ............ ......... .... .. ..... ... .. ....................... 83

6.5.1 Gouge Force with Aspect Ratio ..... ... ....................... ..... .. .... ................ ...... 83

6.5.2 Force Ratio ......................... ....... ........ ... ...... ...... .............. .... ....................... 85

6.6 Comparison with Medium Scale Te t .... .... .... .. .............. .... ........ .......... ... ......... 87

6. 7 Subgouge Deformation ...... ... ........ ...... ... ... ...... .. ............. .......... ..... ...... .... .... .. .... . 91

6.8 Gouge Rate ..... ........ ............ .. ...... ............. ............ .................... .............. ...... ... .... 98

7 CONCLUSION AND RECOMMENDATIONS ... .... .... ........ ............ ... ............ .... . 101

8 REFERENCES ............................ ....... ............ ..... ... .. ......... .. ... ........... ........... .. ..... ... 104

APPENDIX A

v

LIST OF FIGURES Figure 1-1 Ice gouge, La nan et al. ( 1986) ...... .................................. ................................... 2

Figure 1-2 Keel side slope angle ........ .. .......... .... ..... .... .... .... .. ... .. .... .. ... .. .... ..... ...... ...... .... .... . 3

Figure 1-3 Small scale test in sand width 0.5 m, Clark et al. (1990) ...... ....... .... ........ ......... 5

Figure 1-4 Force vectors with keel angle, Vershinin et al. (2007) ......... .. .... ............. ......... 6

Figure 1-5 Ice gouge life cycle, La nan et al (1986) ....................... ......... ................. .... ... .. 10

Figure 1-6 Three zones under the ice gouge, Palmer et al. (1990) .......................... ......... 13

Figure 2-1 Centrifuge scaling ..... .. ... ..... ... .... .. ... ... ........ .......................... ..... .. ... ... ... ... ........ 18

Figure 2-2 The distribution of vertical stress in the model and prototype, Taylor (1995) 20

Figure 2-3 Comparison of stress variation with depth in a centrifuge model and its

corresponding prototype, Taylor (1995) ........ .. ... ... ....... ..... ... .. ..... .. .... ......... ........... ... 20

Figure 3-1 Acutronic 680-2 geotechnical centrifuge schematic(C-CORE) .. ..... ........ .. ... .. 24

Figure 3-2 Acrylic wall box ...... ........... .. .... .... ... ... ........ ... ....... .. .... ................. ...... .. ... ... .... .. 26

Figure 3-3 Plane strain box ........... ....... .... .... .. ..... .. .... .. ............... .... ... .... ... ...... ... ..... ..... ..... . 26

Figure 3-4 Dimension of these two model ice keels in mm ......................... ...... ..... ... ..... 28

Figure 3-5 Location of the load cells ................... ...... ........ .......... ... ... .... .. ....... ..... ......... .... 28

Figure 3-6 Actuator side view ............ .... .. .... ........... .. ....................... .. .... ...... .. ................... 29

Figure 3-7 LVDT' S location ........................................................................... .. .. ........... .. . 30

Figure 4-1 Setup of the sand raining tool.. ... .... ....... ..... ............ ......... .. .......... .. ... ..... ........ .. 33

Figure 4-2 Model configuration .. ........... .... .. .... ..... ... ................ ..................................... .... 34

Figure 4-3 Configuration of the sample container during saturation proce .................. . 36

Figure 4-4 The initial sand mound ................... ..................................... .. .. ............. .. ......... 36

Figure 4-5 Model saturation system ....... ..... .. ........ .... ...... ... ..... .... .... ........... ... ..... ......... .. .. . 37

Figure 4-6 Autocorrelation function and hi-cubic approximation being used to determine

the displacement of a patch, White et al.(2003) .. ........... ... ........ ..... ... .... ................. ... 40

Figure 4-7 Cenhifuge model test of ice gouging with photographic reference field at test

start and end ............... ... .. ......... ..... ......... ... ..... .... ....... ...... ....... ..... ..... .... .. .... ...... ... ... ... 41

Figure 5-1 Top view and side view ofvertical Load Cells arrangement.. .... ..... .......... .. .. . 44

Figure 5-2 Model vertical Load versus ice keel displacement for test P02 ..... ......... ........ 46

Figure 5-3 Model vertical Load versus ice keel displacement for test P03 ...... .... ... ......... 46

Figure 5-4 Model vertical Load versus ice keel displacement for test P05 .. ... ... ... .. .. ...... . 47

Figure 5-5 Model vertical Load versus ice keel displacement for test P06 ...................... 47

Figure 5-6 Model vertical Load versus ice keel displacement for test PO? ..... ..... ..... .... ... 48

Figure 5-7 Model vertical Load versus ice keel di placement for test P08 ... .. ...... .... .. ..... 48

Figure 5-8 Model vertical Load versus ice keel displacement for test P09 ...................... 49

Figure 5-9 Model total vertical and horizontal loads versus ice keel displacement for test

P02 ... .. .. ...... .. ... ... .......... .... .. ... ... .... ..... ... ...... .... ...... .... .... ....... ............ ..... .. ... ... ....... ...... 49

VI


P03 oooooooooooo oooooooooooooooo oo ooooooooo oo oo ooooooo oooo ooooooo ooooo ooooooo ooooooooooooo oo oo oooooo ooooooo ooo ooo ooo ooo ooooo oo oo 50


P05 ooooooooooooooooo ooooooooooooooooooooooo oo ooooo oooo oo oooo ooooooooooooooooo oooooooooo ooo ooooooooo oo oooo oo oooooooooo ooo oo ooo oo 50


P06 oooo ooooo ooo oo oo oooo ooooo ooooo ooooo ooooo ooo ooo oooooooo oooooooooooooooooooooooooooooooo ooo oo ooooo oooo oo oooo oo oo ooo oo ooooo oo oo 51


P07 oooooooooo oo oooooo oo oo oo oooo oo ooo ooo ooooo ooooo ooo ooo ooooooooo ooooooooooooo ooooooooooo oo ooooo oooooo oo oooooo oooooo oo .ooo oo oooo 51


P08 ooooooo oo oooo ooooooo oooo oooo oooo ooo oo ooo ooo ooo oooooooooo oooooooooooooooooo ooooooooooo ooo oooo ooo ooooo oooo oooo oooooo oooo oo oooo 52


P09 oooo ooo ooooo oooooooooooooooooooooooooooooooo ooooooooo ooooo ooo ooooo oo ooo ooooooooooooooooooooooooo oooooo oooo oooooooo ooo oo oooo o 52

Figure 5-16 Forces and horizontal deformation accumulation with keel movement for

P08 oo ooo oooo ooooo oooo ooo ooo ooo oo ooooooooooooo oooooo oo ooOO Oooooooooooo oO Ooo oooooooooooooooooooo ooooooooooooooooooooooo• oo ooo oo oo 54

Figure 5-17 Maximum SGD accumulation in a period of time 120mm ahead of basal keel

comer ooooooooooooooooooooooooo oooooooooooooooooooooooo ooooo oooooo oooo ooo oooooo oo oooooooooo ooooooooo oooooooooo ooo oooo ooo ooo ooo 54

Figure 5-18 PIV subgouge defonnation for frame 2-14, displacement of 6705 mm,

Magnification x 10, P02o oooo oooo oo ooooo ooo ooo ooooooooooooooooooooo oooooooooooo oooooo oo ooo ooo oooooo oooooo ooo ooo ooo ooo 55

Figure 5-19 PIV subgouge defotmation for frame 26-32, displacement of 15402 mm,

Magnification x1 0, P02ooooooooooooo ooo oooooo ooooo oo ooo ooooooooo ooo ooo oooo oo oooooooooooo ooooo oooo oo oooo ooo•oooo ooo oo 55

Figure 5-20 PIV subgouge deformation for frame 34-36, displacement of 17305 mm,

Magnification x1 0, P02oooo oooooo oo ooo ooo oooo ooooo oo oooo ooooooooooooooooooo oooooo ooooo ooo ooo oooo ooo ooo oooo oo oooooo oo 56

Figure 5-21 PIV subgouge deformation for frame 6-18, displacement of9306 mm,

Magnification x10, P03oooooooooooooooo oooooo oooooo ooo ooo ooooo ooooooooo ooooooooooooo oooooooo oooooo oooooo oooo ooo oo oo o 56


Magnification x1 0, P03 oo ooo oo oooo oOOO ooo o•oooo oooooo ooooo oooo oo ooooooo oo oooooooooooooooo ooooooooooooooooo ,ooo oo ooO O 57


Magnification x20, P05o oo ooo oooo oooooo oooooo oooooo oooooooo oo oo ooo ooo oo ooo oo oooo oooooo oooooo ooooo oooo ooooooo oooo oooo 57

Figure 5-24 PIV sub gouge deformation for frame 19-21 , displacement of 34605 mm,

Magnification x20, P05 oo oooooooooooooooooooo ooo oo oo oooo oooo ooo ooo oooooooooooo ooooo ooooo ooo ooooo ooooo oo oooooo oooooo o 58

Figure 5-25 PIV subgouge deformation for frame 19-21 , displacement of 17801 mm,

Magnification x20, P06oooooooooooooooo ooo ooo oo oo oooooooo oooo ooooooooooooo ooo oooo oooo oooo ooo oooooooo oooooooO OOOo oOOO 58

Figure 5-26 PIV subgouge deformation for frame 24-31 , displacement of 26209 mm,

Magnification x20, P06oooooooooo oooooooooooooooooooooooooooooooooooooooooooooooo 00000000000 00 oooooooo oooooooo ooo ooo 59

Figure 5-27 PIV subgouge deformation for frame 7-9, displacement of24609 mm,

Magnification x 10, P07 00 000 00 000 0000000 00 000 000000 00000 000 Ooo 00000 00 00 00 00 0 00000 0 00 000 0 000000 0000 0 oo ooooo o 00 000 00 00 59

Figure 5-28 PIV subgouge deformation for frame 10-13, displacement of356o7 mm,

Magnification x 10, P07 00000 00 0 000 000000 000 000 000 00 000 000 00 000 00 000 00 0000 000000 00 00 000 000 00 00 0 000 00 00 000 00 000 000 0000 60

VII

Figure 5-29 PIY subgouge defonnation for frame 35-46, displacement of209.9 mm,

Magnification x10, P08 .. .............. .... .. ........... ......... ...... ..... ............. ...... ................... .. 60

Figure 5-30 PlY subgouge defonnation for frame 28-37, displacement of 175 mm,

Magnification x10, P09 .. .. .............................. ...... ................... ...... ..... ... .................... 61

Figure 5-31 PlY subgouge defonnation for frame 37-45, displacement of212.8 mm,

Magnification xlO, P09 ....................................... .. ............. ............. .. ............. ........... 61

Figure 5-32 PIY subgouge defonnation for frame 53-65, displacement of307.4 mm, ... 62

Figure 5-33 Horizontal movement profile below keel elevation for test P02 ......... .... .... .. 62

Figure 5-34 Horizontal movement profile below keel elevation for test P03 .. ... .............. 63

Figure 5-35 Horizontal movement profile below keel elevation for test P05 .............. .... . 63

Figure 5-36 Horizontal movement profile below keel elevation for test P06 .... .... .. ....... .. 64

Figure 5-37 Horizontal movement profile below keel elevation for test P07 .. ................ . 64

Figure 5-38 Horizontal movement profile below keel elevation for test P08 ................... 65

Figure 5-39 Horizontal movement profile below keel elevation for test P09 .......... ......... 65

Figure 5-40 Sub gouge horizontal displacement for P02 ....... ...................... .... .. ....... ..... .. .. 66

Figure 5-41 Subgouge horizontal displacement for P03 ...... ....... ... ........ ........................... 66

Figure 5-42 Sub gouge horizontal displacement for P05 ............. ........... ..... ...... ....... ... ...... 67

Figure 5-43 Sub gouge horizontal displacement for P06 ................... ..... ......... .... .......... ... . 67

Figure 5-44 Subgouge horizontal displacement for P07 .... ... ... .. ... .... ............. ... ....... ....... .. 68

Figure 5-45 Subgouge horizontal displacement for P08 ....... ... ... ......... ......... .............. ..... . 68

Figure 5-46 Subgouge horizontal displacement for P09 ................... .................. ..... ........ . 69

Figure 5-47 Side view of gouge shape for test P05 ........... .. .... ... ...... .. ... ............ ............... 70

Figure 5-48 Top view of gouge shape for test P06 ......................................... .... .............. 70

Figure 5-49 Top view of gouge shape and dimension for test P03 ............ ..... ................. 71

Figure 5-50 Top view of gouge shape and dimension for test P05 .......... ... ...... ............... 72

Figure 5-51 Top view of gouge shape and dimension for test P06 ...... ...... ........... ........ ... 73

Figure 5-52 Top view of gouge shape and dimension for test P07, mm .............. .. .. ........ 74

Figure 5-53 Top view of gouge shape and dimension for test P08, mm ................... .. ..... 75

Figure 6-1 Frontal bem1 height as multiple of gouge depth, k ..... ......... ... ... ....... .............. 78

Figure 6-2 Kappa value from different test program .............. ...... ....... .. ........................... 80

Figure 6-3 Kappa value versus aspect ratio for PI RAM and PRISE tests ... .... ..... .... ........ 80

Figure 6-4 Keel bearing pressure on gouge and bem1 surcharge C-CORE (2009b) ... ..... 82

Figure 6-5 Bearing pressure versus gouge depth ... .. ...... ... .. ..... ... ....... ... .. ........... ....... ........ 82

Figure 6-6 Prototype horizontal force per unit width versus combined depth ... ..... .. ....... 83

Figure 6-7 Hmizontal gouge force normalisation C-CORE(2009b) ............... ........ ..... .... 84

Figure 6-8 Lateral gouge force comparison of empirical and analytical functions .... ...... 85

Figure 6-9 Prototype force ratio to the aspect ratio ........ .......... ............. ........... .... ........ .... 86

Figure 6-10 Comparing force ratio to the aspect ratio with PRISE and MUN 1 g test 1990

······· ···· ···················· ····· ···· ······· ······· ·· ··· ···· ·· ··· ·· ·· ··· ······ ··············· ··· ································ 86

Ylll

~--------------------------------------------------------------------

Figure 6-11 Horizontal sub gouge deformation of the DH test Run 2 and PIRAM test P05

and P08 ..... .. .............. .. ........ ...... ................. ............................ ........ ...... .. ......... ........... 89

Figure 6-12 Force ratios of the DH test Run 2 and PIRAM test P05 and P08 .. ............... 89

Figure 6-13 Gouge force per unit width versus combined depth between DH Run2 and

PIRAM tests P05 and P08 ............................................................. .. .......... .. .............. 90

Figure 6-14 Normalized horizontal subgouge defonnation of the DH Run 2 and PIRAM

test P05 and P08 ............... ... ............... ............... .......................................... .. ............ 90

Figure 6-15 PIRAM model sub gouge horizontal displacement profiles .......................... 92

Figure 6-16 PIRAM prototype sub gouge horizontal displacement profiles ..................... 92

Figure 6-17 Normalized PIRAM prototype sub gouge horizontal displacement profiles. 93

Figure 6-18 Normalized PRISE and PIRAM model subgouge horizontal displacement

profiles ........................ .. .................... .... .. ........ .. ...... ..... .... ... ......... ... .. .. ............ .......... 93

Figure 6-19 PIRAM model subgouge horizontal displacement profiles C-CORE (2008)95

Figure 6-20 PIRAM model subgouge horizontal displacement profiles C-CORE (2008)96

Figure 6-21 PIRAM model subgouge horizontal displacement profiles C-CORE (2009e) .

........ .. ....... ..... .............. ... .......... .......... ... ... ... ..... .. .... .... ....... .. ....... ..... .... ..... .. .. .... ....... ... 97

Figure 6-22 Subgouge deformation of the PIRAM test P09 and PRISE test PR01 C-2 ... 99

IX

LIST OF TABLES Table 1-1 DH Flume (Vershiniin et al. , 2007) medium scale sand test parameters ........... 7

Table 1-2 Memorial University (Poorooshasb, F. 1990)1g physical model sand test

paran1eters .................. ....... .... ... ......... .. ...................... .................................................. 7

Table 1-3 Memorial University (Paulin, 1992) 1 g physical model sand test parameters ... 8

Table 1-4 PRISE (Phillips et. al., 2005) centlifuge sand test program prototype

paran1eters .... .. .......... .. .... .. .... .............. ........................... .. .................. .......................... 9

Table 1-5 Ice gouge parameters with pipeline design, Comfort & Graham (1986) ......... 11

Table 2-1 Centrifuge sand test prototype parameters .......... .... ........ .. ........... .. .... .... .......... 17

Table 2-2 Centiifuge scaling relationship ........................ .. ................ .. ........................... .. 21

Table 2-3 Centrifuge scaling relationship using viscous fluid .......................................... 22

Table 4-1 Index properties and classification of tested sand ............................................ 32

Table 5-l Sand test results in prototype parameters ...... ................ ........ .... ...... ................. 45

Table 6-1 Sand test results for vertical and holizontalloads in prototype parameters ..... 76

Table 6-2 Model sand settlement during preparing and centrifuge testing ...................... 78

Table 6-3 Sand test results and kappa value in prototype parameters .. .. .. ..... ........ .......... 79

Table 6-4 Comparison of the DH test Run 2 and PIRAM test P05 and P08 .. ................. 88

Table 6-5 Sand test results in prototype parameters ........................................................ 95

Table 6-6 Subgouge relationship parameters ................ .. ................................................. 96

Table 6-7 Compalison of the PIRAM test P09 and PRISE test PRO 1 C-2 ...... ............ ... I 00

X

NOMENCLATURE

Cv coefficient of consolidation

d diameter of penetrometer

D5, D gouge depth

Dr relative density

F11 Horizontal component of gouge force

Fv Vertical component of gouge force

I r Dilation index

N gravitational acceleration

v penetration rate I keel velocity

V nonnalised penetration rate

V* nonnalised gouging rate

W gouge width

a gouge attack angle

K frontal berm height as multiple of gouge depth

v pore fluid viscosity

O"b bearing pressure

XI

.--------------------------------------~----

1 INTRODUCTION AND LITERATURE REVIEW

1.1 Introduction

An ice gouge, Figure 1-1 is fonned when an iceberg or pressure ridge keel is propelled

laterally in contact with the seabed. Because of an iceberg s massive size, a huge gouge

can be created. Growing ice ridges and multi-year ice floes continuously gouge

continental shelves in arctic regions.

The traces made by ice keel gouge can have multiple lines, such as elongated curvilinear

and linear seafloor incisions. Research indicates some of the important factors that affect

ice gouge, include soil resistance, ice strength, keel geometry and driving force are

variables that need to be considered in an analysis. It is a complex calculation in which

the related factors, alternately or combined act.

The ice gouge event can pose a significant threat on sub-sea facilities such as pipelines,

cables, wellheads and also templates. These sub-sea facilities can be protected from ice

keel damage is by installing facilities below the seabed. In Canada, both arctic and

eastern offshore regions are acquiring more accurate inforn1ation to verify models of ice

keel gouge.

Figure 1-1 Ice gouge, Lanan et al. (1986)

1.2 Gouge Geometry

A gouging ice keel pushes a mound of seabed soil ahead of itself. The soil is brought up

on both sides of the gouge. The width of the gouge is usually many times its depth. The

gouge depth and gouge width usually keep the same level over distances of kilometers.

Despite the large mass of icebergs, the environmental driving forces are more important.

So icebergs move by the driving forces. If icebergs travel at a low velocity, because their

large mass, they nonetheless have high kinetic energy.

2

As shown in Figure 1-2, free floating pressure ridge keel side slope angles have a mean

value of 26.6 degrees (Tim co and Burden, 1997). Phillips et a!. (2005) had indicated that

under steady conditions, the ice keel will have been reoriented and reshaped after

gouging. From field observations, it is assumed that the attack angle between the keel and

the soil is about 15 to 30 degrees.

Gouge characteristics include depth, width, orientation, length, frequency and spatial

density. Many offshore and field studies have focused on the ice gouge. Woodworth et.

al. (1996) observed ice gouge formed in clayey silt at Cobequid Bay in the Bay of Fundy

and in the St. Lawrence estuary. One gouge field has also been observed in southeast

Manitoba, beneath the bed of former Lake Agassiz. The gouges were formed in silty clay

at a water level of about 110m, Woodworth et. al. (1996)

~ fA~-~ ---- -~ -------------------i ---~ ----..c

Consolidated Layer

a ~ k-------------- -~/

Keel

Figure 1-2 Keel side slope angle

3

There is a large amount of data showing measurements of gouge depths and gouge depth

statistics from different areas. Researchers have observed at water depth between 15 m

and 20 m in Alaska' Beaufort Sea coast which include 3046 gouges with a depth of

between 0.2 m and 1.6 m, Weeks et al. (1983). They found that the depth distribution of

ice keel gouges follows a straight line on a semi-logarithmic data plot:

F(x) = .Ae--l<x-c) for x>c. Where, F(x) is the probability density function for ice gouges.

x(k) is ice gouge depth. C (k) is the cutoff depth below which gouge become too small

to identify and count (and the ice gouge depth which all of the observed ice gouges

exceed). A. is a constant specifying the slope of the negative exponential gouge depth

distribution curve, Lanan et al (1986).

1.3 Studies of Ice Gouge

Small-scale physical models and large scale physical models are used to study the ice soil

interaction and subgouge soil movement. To detennine the force and the displacement

under the seabed, Clark et al. (1990) has done small scale tests with 0.5 m for the gouge

width in loose and medium density sand. Figure 1-3 shows the influence of the soil

strength on the sub-gouge deformation, Clark et al. (1990). The small cale tests with 0.5

m for the gouge width in loose sand have larger depth of disturbance below gouge.

The Chari model Chari (1975) is an energy model that considers an ice gouge is driven

by the mass of the iceberg, curTent drag and wind. The resistance of the gouge is

dependent on the length, width and depth of the gouge, the unit weight of the soil and the

4

shear strength of the soil. Surkov' s model, Surkov (1995), is similar to the Chari model in

that they all involve the horizontal translation of an ice feature into a sloped seabed.

Nom1alized Horizontal Displacement (Dtt!Ds)

0 5 10 15 ... 8 0 -f-----..J.._-------'-----------'---~ -· ~ 0.5

-.; CO,....., I -=e fr ~ o e.1.5 1l .!:::: Cii 2

E ~ 2.5

LOOSE SAND •

•

Nom1alized Horizontal Displacement (DH/ Ds)

... 0 5 10 15

"' ~ 0 -f------~_-_-__ - _-_-_-_-_-__ -_~_-_-_ -__ - _-_-_-_-__ -_-_~_-_-_ *~

6 0.5 ... --~-------.; co,....., I -=e c. > Q)o 0 '-' 1.5 13 .t:! Cii

2

E ~ 2.5

DENSE SAND

Dv - Depth of disturbance below gouge

DH - Horizontal displacement

Ds- gouge depth

Figure 1-3 Small scale test in sand width 0.5 m, park et al. (1990)

The Flume test, Vershinin et al. (2007) is medium-scale test of scale 1 :5 to 1:10. A total

of 29 tests were conducted using a half-keel with a glass wall so that it can have visual

information of the process. The subgouge deformations are limited between the bottom of

the keel and 250 mm below the bottom of the keel. The keel model is made by steel with

the attack angles 15 degree, 30 degree and 45 degree. Figure 1-4 shows the force vector .

Increasing the keel angle decreases in horizontal force which is related to the change of

5

r----------------------------------------------~-----------

direction of the friction force on the keel surface. At low attack angles, the friction force

on the keel surface is downwards. Around 30 degree angle, it appears to tum upwards. At

higher keel angle, the friction force is directed upward. Friction along the keel bottom

would increase the horizontal force. Results from these tests indicated that the smaller

attack angle can have the larger defonnation. The sub-gouge defonnation was determined

from digital images by the method of particle tracking.

Trltl RllllllCI Rill 1 kMI modtl 15 c~ta 1.10 m 111cllll

rcrce VIdor-. (1IN]

JC

lC

lC

' - nta1 Rl!n Jf7 nrn

lC ~ ~~ ~ ~ .--- ~

,).--"

Ill! ~ 1---

- ni!llllln 2!!7nrn - 111.111. 18a rr. - Rill!, 1M nm - Rill f&mm

0 0 100200~~3~ 37<1>tJOfOO 01 3) :100

poel10n bi!Ort I!Nltdgl {l1lmJ

RIJI\ 3 • moaet 15 oeg. t n m 1111111\

. ., 500

..... ~ ~ ...--...-~ ~ ~ :.-

-...- ....-0

0 1C!J :s::!l !CD .C::I !C!I K ::l 70::t 63::1 !D::I 1ti:C t :C 12%1

pc5'!1on t<!'cre kul odg! (Jrm)

tOO

'

111.112 keeJ~:lOd<g. 1. omwllll

[\ ' \ \ '\ 1\\ \ \ v ,

.ftl ) <llWl .fiC) .71Xf .. ~ ~D -!00 .xl! · lllO 0 t:al l<13

I J I! B . !!

1

po!lllcn OflorekEEI edge [m1t

IIUn 4 •H 1 rroa.t• s Clfg. 0.75 rr 'A'lCI1ll

12CC

·ccc-

! Cl

!CD

4Cl

l CD

\ \n,, il ·1i 0C · t 5JJ ·1• 1X .lQO •ttXI ~CI:i · UJ ~CO •: JO

po.':bn D!l'ore IHI ~dgo (mm)

Figure 1-4 Force vectors with keel angle, Vershinin et al. (2007)

v

6

Table 1-1 DH Flume (Vershiniin et al. 2007) medium scale sand test parameters

Attack Gouge Gouge Test angle, Depth, Velocity, Fv F" Dr% Width, Ir FviF11 Kappa

I. D. o: (deg) D (m)

W(m) ( n11111sec) kN kN

Run 2 30 55 0.19 2.2 2.2 13 67 48 1.39 1.55

test I

Run2 30 55 0.19 2.2 2.1 12 98 77 1.27 2.51

test2

Run 2 30 65 0.19 2.2 2.3 20 213 147 1.45 2.85

test3

Poorooshasb (1990) undertook medium scale tests in clean silica sand. This research

focused on the magnitude and extent of subgouge displacement and finding out if the

attack angle, keel width and sand density could affect the gouging progress. The test was

using aluminum model ice keel with attack angle 15 degree or 30 degree. This test uses

strands of solder and ball bearings to determine the subgouge displacement. Poorooshasb

(1990) indicated that the denser the sand density was, the smaller the subgouge

defonnation would be. The I 5 degree keel model test has higher deformation than 30

degree keel model test. The primary direction of displacement was in the direction of

travel of the gouging feature.

Table 1-2 Memorial University (Poorooshasb F. 1990)1g physical model sand test parameter

Attack Gouge Gouge Relative Fh Fv

Test Soil Type Angle Depth Width Density

(deg.) (m) (m) (kN) (kN)

Poor 2a Loose Sand 0.09 15 0.075 0.86 6.5 7.25

Poor 2b Medium Sand 0.33 15 0.075 0.86 8.0 9.0

7

Paulin (1992) undertook a series of 4 silica tests to continue the Poorooshasb's (1990)

sand tests. Paulin (1992) tests were focused on the observation and measurement of the

limits of subgouge deformation. The instrument used in Paulin (1992) is similar to

Poorooshasb (1990) tests. The test was using aluminum model ice keel with attack angle

of 15 degree. Pressure transducers and load cells were used in Paulin ( 1992) test.

Horizontal and vertical subgouge displacement, stress response in the soil and the effect

of pore fluid were measured in the tests. Paulin (1992) concluded that horizontal

displacements were larger than the vertical displacements.

Table 1-3 Memorial University (Paulin, 1992) 1 g physical model sand test parameters

Test Soil Type Dry Attack Gouge Gouge Fh Fv

Density Angle Depth Width (kN) (kN)

(kg/m3) (deg.) (m) (m)

Paulin 3 Wet Sand 1365 15 0.038 0.43 0.768 0.969

Paulin 4 Wet Sand 1363 15 0.040 0.43 0.799 0.826

The Pressure Ridge Ice Gouge Experiment (PRISE) led by C-CORE was focused on

"developing the capability of designing pipelines and other seabed installations in regions

gouged by ice, taking into account the soil deformations and stress changes, which may

be caused during a gouge event", Phillips eta!. (2005). The PRISE includes five research

phases:

• Phase 1: PRISE Planning and Extreme Gouge Dating Project Feasibility Study

• Phase 2: Extreme Gouge Dating Project

• Phase 3: Centrifuge and Numerical Modelling, Pipeline Design Guidelines

• Phase 4: Full-Scale Ice Keel/Seabed Interaction Event

• Phase 5: Full-Scale Ice Keel/Seabed/Pipeline Interaction Event

8

Table 1-4 PRISE (Phillips et. a!., 2005) centrifuge sand test program prototype parameters

Relative Attack Gouge Gouge Fh Fv

Test Soil Type Density Angle Depth Width (MN) (MN)

(deg.) (m) (m)

Phase 3a

PR01B-2 Fine Sand 37.4% 15 1.7 15 33.7 35.1

PR01C-1 Fine Sand 37% 30 0.98 15 8.9 8.4

PR01C-2 Fine Sand 37% 15 1.1 15 12.2 14.2

PR09-l Fine Sand 47.2% 15 1.2 15 19.3 16.4

PR09-2 Fine Sand 47.2% 15 2.14 15 40.3 38.5

PR10-1 Fine Sand 65.9% 30 1.19 30 40.5 38.0

PR10-2 Fine Sand 65.9% 15 1.16 30 45.9 49.9

Phase 3c

PRSA01 Fine Sand 81% 30 4.5 15 93.8 123.3

PRSA02 Fine Sand 90% 15 2.50 7.5 24.6 28.6

PRSA03 Fine Sand 55% 15 2.10 15 64.4 56.9

PRSA04 Fine Sand 82% 15 2.66 15 74.4 67.3

PRSA05 Fine Sand 69.5% 15 2.5 15 67.3 63.7

Centrifuge modeling was conducted in Phase 3, which is important for detem1ining the

subgouge deformation. Phase 3 centrifuge modeling included 9 centrifuge te ts in clay,

and 20 centrifuge tests in clay, sand, and layered clay/sand soil. The main parameters for

the tests were soil type, soil condition, attack angle, gouge width and gouge depth. Gouge

depth for sand tests is from 0.98m to 4.5m. Gouge width for sand tests are 7.5m, 15m,

and 30m in prototype. Attack angle are 15 degree and 30 degree (Table 1-4). The PRISE

9

sand tests focused on the significance of subgouge deformation to assess the safe burial

depths for pipelines against ice gouging. These sand tests are compared with PIRAM

tests in section 6.5.

1.4 Theorical and Numerical Studies

1.4.1 Ice Gouge Life Cycle

Because the gouge is fonned by the ice keel driving across the seabed, soil is heaped on

each side of the gouge. After the ice keel moves away, the soil piled on each side may

flow back into the gouge, so the gouge depth will be reduced, Figure 1-5. After the ice

gouge has fonned , it will not keep the same depth but wi ll keep changing. The gouge will

become partially infilled.

GOUGE I FILL BETWEEN t0 AND t1

_...___,. ............. ,'lll"'llli

(ORIGINAL GOUGE P'ROFI )

Figure 1-5 Ice gouge life cycle, Lanan et al (1986)

10

1.4.2 Ice Gouge Parameters with Pipeline Design

There are some necessary components for ice gouge. These include the width of the keel,

the depth of the gouge, the contact angle of the ice keel, which are the important

parameters for offshore pipeline design. The relationship between ice gouge parameters

and offshore pipeline design is shown in Table 1-5.

Table 1-5 Ice gouge parameters with pipeline design, Comfort & Graham (1986)

Ice gouge parameters Effect on pipeline design

Gouge depth Design trench depth

Keel width Requirement of damage and repair

Keel residence time Potential for accessibility to repair site

Variation with water depth Establishes practical use of dredging equipment

Critical exposure period Influence repair response

Directionality of gouge Influences risk and length of potential damage for

specific routes

Mechanism of gouge Defines feasible methods of protection

Keel-soil interaction

A vail able forces

Keel strength

Keel shape

Correlation to surface ice Defines feasibility of installation repair

conditions

Influence of structure Defines special requirements for trenching near

structures

Frequency of occurrence Defines trench depth

11

-~ ----------------------------------- --- - - - - -· - --

The parameter of the keel residence time is related to the time needed for repair. The

variation of ice gouge with water depth is important for designing the offshore pipeline

because it detetmines the equipment used for trenching the pipeline. The directionality of

gouge is impmiant in estimating the higher risk but shmier length of damage, which is

important for economic consideration. The method of burying and covering pipeline is

dependent on the mechanism of gouge. The parameters of influence of structure and

correlation to surface ice conditions are more related to the operational aspects.

1.4.3 Pipeline Trench Depth

To avoid damage by ice gouge, the pipe may be required to be buried in a trench below

the ice gouge level. There are many factors influencing pipeline depth, such as the

behavior of the ice keel, the backfill, the level of the risk that can be accepted, and so on.

For designing the pipeline, it is important to know the geometry of the ice gouge. The

next one which is also impmiant for designing pipeline is how much forces will be

transferred from the ice keel to the seabed and thus to the pipeline.

It is generally agreed that the ice gouge depth can in some pati decide the pipeline burial

depth. If the ice gouge depth is more than the pipeline burial depth, the pipeline will be

dan1aged. If the pipeline burial depth is larger than the ice gouge depth, there may not be

significant damage on pipeline by ice gouge

Palmer (1990) has assumed three zones of deformation, Figure 1-6. Zone 1 is a zone of

large defom1ation in which the soil is moved by ice keel. Zone 2 also has large

12

defonnation that the soil has plastic defom1 and the location is under the ice keel. Zone 3

is a zone with small elastic deformation. It is easy to see the boundary between zone 1

and zone 2. This boundary is defined by the gouge depth. The boundary between zone 2

and zone 3 can be seen as separate in that the deformation in zone 2 is plastic and the

deformation in zone 3 is elastic. It is affected by the driving force, oil type, ice geometry

and so on.

A pipeline located in zone 1 is likely to fail in the event of an ice gouge. The pipeline in

zone 3 will be safe because there is little deformation in zone 3. However, locating a

pipeline in zone 3 may not be economically viable because of the buried depth. The best

choice for located the pipeline is in zone 2. In zone 2, there are two aspects to affect the

pipeline. They are gouge load and soil displacement. So the combination of the gouge

load and soil displacement is the largest damage for the pipeline in this zone. In order to

design the pipeline, it is important to calculate the gouge load and soil defom1ation.

ZOM2 - -------- -z;;;-c

Figure 1-6 Three zones under the ice gouge, Palmer et al. (1990)

13

King et al. (2008) presented a methodology for a probabilistic pipeline burial analysis for

protection against ice gouge. Through a first-order estimate of required pipeline cover

depths for a hypothetical gas pipeline on the Grand Banks, the results demonstrate the

need to properly combine both ice gouges and pits into the overall scour tisk analysis, as

well as the influence of ice management on pipeline cover depths required to meet target

annual reliability levels.

1.5 Research Objective and Outline

Ice gouging can have detrimental effect on subsea facilities such as wellheads, pipeline

and submarine cables. To help understand the significant effect, a large amount of

research has been undertaken. Due to field study, small scale physical modeling and large

scale physical modeling, the process of ice gouging, ice soil interaction, the profile of

subgouge defom1ation have been understand. As mentioned in section 1.3 experimental

studies, many studies has been undertaken before. Delft Hydraulics Flume tests were

conducted in small gouge depth. PRISE tests were conducted in sand and clay with large

gouge depth. All the previous tests mentioned are conducted in sand saturated with water.

PIRAM test which has the objective of developing practices for risk mitigation and

protection of pipeline infrastructure from ice keel loading, is developing a set of

engmeenng models to establish probabilistic estimates of the pipeline mechanical

behavior in response to ice keel load events, and assess engineering concepts of

protection and risk mitigation strategies. The development of methodologies to detem1ine

contact frequency and ice keel loads will also fom1 part of the integrated model.

14

As the component of PIRAM tests, this thesis focuses on the magnitude and the vertical

extent of subgouge deformation by PlY techni9ues. The established experimental

objectives included modeling 7 tests using fine sand saturated with viscous pore fluid to

retard the di ipation of excess pore pressures, comparing with previou Delft Hydraulics

flume medium scale gouge tests to evaluate the applicability of centrifuge modeling. The

effects of fast gouge rates in fine sands was a focus as much previous work was

conducted at a relatively slow rate.

This thesis comprises seven chapters. Chapter I is an introduction and literature review

which presents the general defom1ation of ice keel gouge and the various

phenomenological, analytical, and experimental studies from previous re earchers.

Chapter 2 establishe the principle of centrifuge modeling and discus e the relationship

of the scales between the experimental model and prototype. Chapter 3 describes the

equipment u ed for the PIRAM experiment. The procedure of the experiment and the

theory of the saturation are presented in Chapter 4. Chapter 5 and Chapter 6 establish the

experiment results, analysis and comparison with previous tests. A discussion of the

results and the conclusions are presented in the final chapter.

15

2 CENTRIFUGE MODELING

2.1 Introduction

A centrifuge is a load frame that is used to test soil models, and plays a major role in

geotechnical engineeting. The model is placed at the end of the centrifuge ann and is

rotated about the central axis of the centrifuge. At a high-speed rotation, the model can

have a much higher acceleration in the radial direction than that of earths gravity. As the

pressure of the soil increases through the depth of the soil, a small-scale model placed on

the centrifuge can provide a similar stress profile as the prototype.

A total of seven tests were conducted in the centrifuge, Table 2-1. The first six tests were

conducted using a keel with an attack angle of 30 degree. However the attack angle for

the last test was 15°. The two first model tests were conducted relatively slowly in dry,

dense, and water-saturated medium density sand to prove the new equipment and

techniques. Two tests are included for comparisons to previous Delft Hydraulics flume

medium scale gouge tests, to evaluate the applicability of centrifuge modeling. Three

tests are conducted with faster gouge rates using a viscous pore fluid to retard excess pore

pressure dissipation

16

~---------------------------------------------------------

Table 2-1 Centrifuge sand test prototype parameters

# Test Attack Gouge Gouge W/ Ds Dr Saturation G Keel

I. D. angle depth width (%) condition level speed

a (deg) (m) (m) (mm/sec)

1 P02 30 1.3 10 7.6 93 .6 Dry 55.6 0.5

2 P03 30 1.4 10 7.0 51.5 Water 55.6 0.5

3 P05 30 0.18 2.2 12 58 30 est 12.2 1.1

4 P06 30 2.3 14.4 6.25 50.8 30 est 80 1.1

5 P07 30 2.4 14.4 6.0 39 30 est 80 5.5

6 P08 30 0.19 2.2 11.3 68.1 30 est 12.2 55

7 P09 15 1.2 16 13.3 38.6 30 est 80 57

2.2 Centrifuge Modeling Principle

A soil model that is loaded on the end of the centrifuge arm is rotated around a central

axis of the centrifuge. During the rotation progress, the model can get the radial

acceleration that provides a higher gravity than Earth. The increased radial acceleration

ro} is equal to Ng, where w is the angular velocity of rotation expressed in radians per

second, r is the distance between the object and its axis of rotation and g is the

gravitational acceleration, Taylor (1995). When the model and the prototype is using the

same soi I and has the acceleration of N times of the Earth ' s gravity, the vertical stress at

depth h111

will be identical to that in the corresponding prototype at depth h P where

hP =N h111

, Taylor (1995). This is the basic scaling law of centrifuge modelling. Figure 2-1

17

h

t / Full Scale or Protype

hl n Model

a= png(hl n) = pgh

Figure 2-1 Centrifuge scaling

2.3 Scaling Law for Modeling

According to the basic law above, if a model which has the density of p and acceleration

ofN times Earth's gravity, then the vertical stress o-,11

at depth h, in the model is:

a-.,,= pNgh, Equation 2.1

In the prototype it is:

Equation 2.2

Where: p represents mass density, g represents earth' s gravitational acceleration and h is

the depth, Taylor (1995).

As the model is the linear scale of the prototype, so the displacement will also have a

scale factor of 1: N. In order to maintain the vertical stress of the soil model at the same

level as the vertical stress of the prototype, it is apparent that either the density or the

18

gravity of the model should beN times that of the prototype when the soil depth of the

model h111

is 1/N times of the prototype h P from the equations 2.1 and 2.2 above. As it i

not easy to change the density a lot, the acceleration g must be N times of the Earth' s

gravity which i pre ent below, Taylor (I 995):

Equation 2.3

For the non-linear variation of stress in the model, the vertical stress at depth z in the

model can be determined from:

rz 2 2 z CY..,, = Jo pm (R, + z)dz =pOJ z (R, +2) Equation 2.3

Where: R, is from the radius to the top of the model.

According to the Taylor (1995), there is an exact conespondence in stre s between model

and prototype at two-thirds model depth. The effective centrifuge radius should be

measured from the central axis of the centrifuge to one-third the depth of the model. As

the equation shows below:

R = R +~ e 1 3

Equation 2.5

Where: Re is the effective radius.

The maximum enor is given by equation 2.6:

h r = r = - '-"

II 0 6R e

Equation 2.6

Where: '~, IS the maximum under-stress, r0

is the maximum over-stress. As most

geotechnical centrifuge has the h111

IRe less than 0.2, the maximum eJTor in the stress is

minor and less than 3% of the prototype stress. The distribution of vertical tres in the

19

model and prototype is shown in Figure 2-2. The comparing of the vertical stress of the

model and prototype is shown in Figure 2-3 after Taylor (1995)

w Q

'

w'r = N g 0 MODEL

h

' DEPTH

VERTICAL STRESS

p g H

g '

H = N h

PROTOTYPE DEPTH

VERTICAL STRESS

p Cl H

Figure 2-2 The distribution of vertical tres in the model and prototype, Taylor (1995)

EFFECTIVE RADIUS

VERliCAL STRESS

~---------------------------------1--

h I 3

2 h I 3

h

MODEL DEPTH

UNDER STRESS

OVER STRESS

MODEL PROTOTYPE

CONCURRENT STRESS

Figure 2-3 Comparison of stress variation with depth in a centrifuge model and its

corresponding prototype, Taylor (1995)

20

Using the inverse relationship between model and prototype length as a starting point, for

example, the volume occupied by the model ( V,,) in relation in relation to the volume of

the prototype ( vp ) is given as

V =-1- V S = -

1- · m 3 P o Jnm 3 m P N N

The centrifuge scaling relationships are shown as Table 2-2

Table 2-2 Centrifuge scaling relationship

Physical Quantity Model atNg

Gravitational acceleration N

Linear dimension 1/N

Area 11 N2

Volume 1/N3

Mass 1/Nj

Velocity 1

Stress 1

Force 1/N2

Strain 1

Soil density 1

Fluid density 1

The non-dimensional Terzaghi time factor T for consolidation IS defined as C,~L . d

As d P = nd111

, so T," = ~ TP ( C.,P ) . Cv = _ k_ where k is Darcy penneabilty coefficient n c.,/11 JLm.,

21

--------------------------------------- ------

and m" is compressibility of soil. k and m,, are all related to soil and J.1 is the pore fluid

prope1ties. We know the model using the same soil as prototype, so we can do 'part' of

the nom1alisation using pore fluid viscosity which can bring J.l, = m . So ~~~ = 1~ TP. J.lp n

The relationships are shown below.

Table 2-3 Centrifuge scaling relationship using viscous fluid

Time(diffusion with water) 1/NL

Time (diffusion with viscous fluid) MINL

Fluid viscosity ratio M

Velocity (water) N

Viscous fluid velocity (m times viscous than water) N/M

22

3 EXPERIMENT EQUIPMENT AND PRINCIPLES

3.1 Centrifuge

The centrifuge used for all the tests is the Acutronic 680-2 geotechnical centrifuge which

is a beam centrifuge housed in a 13.5 m diameter chamber with 0.3 meter thick concrete

walls. The centrifuge is located in C-CORE on the St. John ' s campus of Memorial

University of Newfoundland. As shown in Figure 3-1 the Acutronic 680-2 geotechnical

centrifuge contains a swinging platform on which the models are tested two parallel steel

tubes which support the platform, an adjustable 20.2 tonne counterweight, a central drive

box and electrical cabinets, pedestal, gear box, motor and drive. The power of the

centrifuge is provided by an AC variable speed motor, with power consumption mainly

due to aerodynamic drag within the centrifuge chamber. The radius of the centrifuge is

5.5 m from its axis to the base of the swinging platfonn. The maximum rotation speed is

189 rpm and the maximum gravity is 200 gravities at a radius of 5 m. The platform can

carry a model up to 1.1 m wide by 1.4 m long by 1.2 m to 2.1 m height in the centre of

the platfom1. The maximum payload that the centrifuge platform can cany is 650 kg

when the rotational speed is 189 rpm. The centre has a circular concrete chamber and a

building containing machine shop, sand raining room, electronics lab, cold room and x

ray facility.

23

Counter Weight Pedestal Shroud

Pivot

I• 2m - •I

Figure 3-1 Acutronic 680-2 geotechnical centrifuge schematic(C-CORE)

24

3.2 Strongbox

Centrifuge models use strongboxes to contain the model soil and to provide a base for

securing other experimental equipment. After preparing the model in the strongbox, it

was carried by a forklift and loaded onto the centrifuge platform for testing.

There are two strongboxes that were used. One box uses acrylic waH box, Figure 3-2,

which weighs 213.6 kg when empty. lt contains two glass walls through which can be

seen the model soil movement during centrifuge testing. The inside dimension of acrylic

wall box is 735 mmx275 mmx394 mm. It has channels machined into the base of the

strongbox for pore fluid pressure movement. The Acrylic wall box has two valves outside

ofthe box connected to the channels in the base of the box, so the pore fluid supply lines

could be connected to both of the valves. For holding the vacuum, the Acrylic wall box

has a cover which can be bolted on the top of the box.

The other strongbox is a plane strain box, Figure 3-3. It has one glass wall from which

model soil movement during centrifuge testing can be seen. The inside dimensions of

Plane strain box is 900 mm x276 mm x294 mm. The empty weight without protective

glass is 304.4 kg.

25

Figure 3-2 Acrylic wall box

Figure 3-3 Plane strain box

26

Channels are also machined into the base of the strongbox. This box has only one valve

on the back of the box. The strain box also has a cover for holding the vacuum which cru1

be bolted on the top of the box and sealed up with Vaseline.

3.3 Model Ice Keel

The test setup consisted of an aluminum half width ice keel model mounted on a gantry

situated on top of the containment box because the centerline of the model was replaced

by a viewing window to visualize the subgouge deformation accumulation. The model ice

keel is made of aluminum plate that is welded together. The attack face which meets the

sand is knurled to increase the interface friction above the angle of the internal friction of

the sand. There are two kinds of model ice keels used in the test. P02, P03, P05, P06,

P07, P08 are using the model ice keel with an attack angle of 30 degrees from the sand

level. The width of the model ice keel is 90 mm. P09 is using the model ice keel with

attack angle of 15 degrees. The width of the model ice keel is 100 mm. The dimension of

these two model ice keels is shown in Figure 3-4 in which all the dimensions are in mm.

In order to measure the vertical load and hmizontal load, there are load cells between the

model ice keel and the carriage and motor respectively. Three 2.2 kN and 4.4 kN

tension/compression load cells ru·e attached to the ice keel and the carriage, which can

measure the vertical load. The location of the load cells is shown in Figure 3-5 There is

one 4.4 kN tension/compression load cell attached to the front of the model ice keel

which is used for measming the horizontal load by connected to the motor through the

steel cables.

27

Figure 3-4 Dimensions of these two model ice keels in mm.

n n

,

f ' lo i

~ y :

n, ~. J

o.ol cell

Figure 3-5 Location of the load cells

3.4 Actuator

4 (

r~oolel keel

The actuator holds the carriage on which is bolted the model keel. It is bolted on the top

of the strongbox. The actuator is designed to provide the horizontal motive force and to

resist vertical motion, Figure 3-6. There are two parallel steel bar on the top of the

actuator for guiding the movement. Four bearings two on each steel bar are bolted

together through two steel plates. The bea1ings can slide on the bars with small friction

resistant which can be ignored compared with the horizontal force and the ve1tical force

that expected during the centrifuge test. A motor is connected to a drive shaft and capstan

connected to the model keel by steel cables. The model ice keel movement is transmitted

through the steel cables by the motor. The moving speed of the model ice keel is

28

controlled by the speed of the motor adjusted by the computer in the control room. There

is a limit switch at the end of the actuator. When the bearings touch the switch, the motor

stops running and the model ice keel stops moving.

steel

J=-L ~~ur I

I 0 {)

c

0

~ ~ (

f=l----1 ~ ~ (

~ § § §

steel plute

-curriuge

Ki-, n -, .--

cel0

[U[ [U

loud qjY

/ l'lodel

/ keel

-Figure 3-6 Actuator side view

3.5 Data Aquisition System

Data aquisition system contains a signal conditioning box, a string potentiometer

LVDT's, four load cells, and two cameras. The string potentiometer was placed at the end

of the actuator and connected to the carriage which is used to get the displacement of the

model ice keel. During centrifuge testing, because of the increased g level, the model

sand will compress and become denser. So the sand level will be reduced. LVDT'S are

located on the side of the actuator and stand on a plastic bearing plate on the top of the

sand to measure the settlement of the sand level, Figure 3-7 After centrifuge test, the sand

29

..-----:----------------------------------------

density can be calculated by the original sand level measured after loading the model on

the centlifuge platfom1 minus the settlement during test. Cameras are used to take

pictures of the sand through the model ice keel moving process. The pictures are analyzed

by PIV method to assess the subsurface sand movement during gouge modeling. The

signal conditioning box is located on the side of the strongbox. All the measuring

equipment are connected to the signal conditioning box. The data is transferred through

signal conditioning box to the computer. The centrifuge acquisition and control systems

are contained in the centrifuge electlical cabinets.

Figure 3-7 L VDT'S location

30

..----:------------------------------------------------

4 EXPERIMENT PROGRAM AND TECHNIQUES

4.1 Introduction

A senes of seven centrifuge model gouge tests were performed and the subgouge

deforn1ation accumulations were tracked usmg particle image velocimetry, PlY

techniques adopted by White et al. (2003). The soil consisted of AlWhite Silica sand. The

characteristics of the soil are presented in section 4.2, while the experimental planning

and identification are described in section 4.3 . Centrifuge tests at a scale of N g's were

conducted on viscous pore fluid-saturated models to retard excess pore pressure

dissipation. This fluid is a solution of a water-soluble polymer derived from cellulose

diluted to M times the viscosity of water, see Table 2-3. The procedure for sample

preparation, the placement of transducers and saturation are presented in detail in section

4.4. Section 4.5 discusses the model instrumentation and data acquisition. The centrifuge

testing procedure is discussed in section 4.6. Section 4.7 presents the particle image

velocimetry, PIV techniques.

4.2 Sand Description

Alwhite Silica sand #00 was used in all tests. Classification tests to determine material

prope11ies for Allwhite Silica sand were conducted according to ASTM specifications.

The sand corresponding index properties and classification are reproduced in Table 4-1.

31

Table 4-1 Index properties and classification of tested sand

Maximum dry density 15.84 g! cm3

Minimum dry density 12.94 g/ cm3

Specific Gravity 2.66

Effective gravity size ( d10 ) 0.1 mm

Mean grain size ( d50 ) 0.3 mm

Unifonnity coefficient (Cu) 3.2

Coefficient of gradation(Cc) 1.25

USCS Group SP-SM

4.3 Testing Program

A total of seven tests were conducted in the centrifuge, Table 2-1. Centrifuge tests were

perfom1ed under drained to undrained conditions using half width models and a viscous

fluid of a viscosity 30 eSt (P05, P06, P07, P08 and P09). The first model test P02 was

conducted in dry dense sand to prove the new equipment and techniques. The second

model test P03 was conducted relatively slowly in water saturated medium sand. Two

tests P05 and P08 were included for comparisons to previous Delft Hydraulics flume

medium scale gouge tests, Appendix A. Three tests P07, P08 and P09 were conducted

with a faster gouge rates using a viscous pore fluid.

4.4 Preparation of Soil Model

The model test bed was rained dry into the centrifuge strongbox from a hopper. The

raining technique consists of pouring dry soil layers through a fixed drop height. Raining

32

can be achieved by using stationary or traveling hoppers. The traveling raining technique

is used in this tudy to control the density of sand over a wide range from a loose state to

a dense one in a stable manner.

Figure 4-1 Setup of the sand raining tool

The hopper shown in Figure 4-1 was manually moved back and forth o er the area of

sample preparation. The relative density of the soil was controlled by the falling height of

the sand and travelling peed of the hopper. Sand pouring is done in thin layers by raising

the hopper the same thickness of layer to obtain a constant height of raining for each

layer. A 100 mm thick layer of coarse sand with particle size larger than 1 mm was placed

before raining the and to distribute the fluid throughout the sample during aturation as

shown in Figure 4-2. The drainage layer was covered with a geotextile layer. The initial

33

soil sand mound as shown in Figure 4-4 is prepared after reaching the final sand level.

The total weight of the dry soil is tracked.

Figure 4-2 Model configuration

rstrongbox

vcourse sand

1/

Hydroxypropyl methylcellulose (HPMC) was prepared by mixing Methocel F50 Powder

at a specific concentration with de-ionized water to reach the required viscosity (say 30

eSt). A mass of Benzoic Acid USP powder equal to approximately I% of the mass of the

HPMC powder is added to the mixture to prevent any bacterial growth that may occur in

the completed fluid batch. After that, the pore fluid reservoir is de-aired for 48 hours.

Figure 4-3 and Figure 4-5 show the configuration of the sample container, vacuum pump,

and fluid tank. The sample is first de-aired by the application of vacuum to the prepared

sand for a period of approximately 48 hours at about 70 kPa. Following this initial

vacuum stage the vacuum pump to the sealed model container is shut off and carbon

dioxide is then used to displace the less soluble air that may be present in the voids of the

34

sand model. Carbon dioxide gas is introduced slowly into the bottom of the model under

atmospheric pressure. Following this process, the strongbox is again placed under

vacuum to bring it back to the 70 kPa vacuum level. The process of introducing carbon

dioxide followed by vacuum is repeated four times to ensure that the majmity of the gas

inside the container is carbon dioxide which is much more soluble in water than air to

allow a more complete saturation. The next step is to open the vacuum to both the

de-aired pore fluid tank and the strongbox to ensure equal vacuum to both containers so

that when fluid is introduced it is not moving by differential pressure that can cause

disturbance to the model. After equalizing the vacuum between the two containers, a

valve is opened to allow the pore fluid to saturate the model from the bottom. It usually

takes 3 days to saturate the sand in the box from the bottom to the top.

4.5 Model Instrumentaion and Data Acquisition

Data acquired during the gouging event included the resultant vertical and horizontal

forces acting on the model keel. The total vertical force was computed through

summation of contributions from the three individual 2.2 kN and 4.4 kN

tension/compression load cells (front, close and far load cells) which linked the model

keel to the carriage assembly. The horizontal force is determined by measuring the

tension in the cable via a 4.4 kN water-resistant tension/compression load cell. The model

keel displacement is measured via a positions transducer while differentiating

displacement with time gives gouging rate. Settlement of the seabed surface was

monitored with one linear variable displacement transducer (L VDT). In test P09 a total of

three pore water pressure transducers (PPTs) were embedded in the model seabed.

35

Figure 4-3 Configuration of the sample container during saturation process

Figure 4-4 The initial sand mound

Digital photography by a CCD photographic camera or a high speed Phantom camera is

used to capture images of soil deformation during ice gouging. There were two additional

cameras mounted on the package to monitor the progress of the test and cable movement.

36

The data acquisition-sampling rate during centrifuge spin-up was set at 10 Hz and during

ice-gouging event was set at 10-500 Hz based on the keel speed.

Data acquisition is perfonned usmg a PC-based data acquisition system. Transducer

excitation voltage and filtering are provided using a custom-designed ignal conditioning

system. Transducer signals are digitized through a 64-channel data acquisition system

contained in a VXI chassis and collected using a Windows-based data acquisition

program called DaqExpress.

I !0. lvocuun I I '<Y I source

~

A

\7 (9 G --- IXJJ·essurizatim

vi=us flui< flLrid Ckarb:r

renvoir lrnp

B (SJ c (~ C02 bottle

'----

n c~ sanol l"lOoiel

"' 0 F

-0 E

Figure 4-5 Model saturation system

37

4.6 Centrifuge Testing Procedure

A centrifuge proof test was undertaken to evaluate the perfom1anc.e of the drive system.

Once saturation is complete, the actuator was put on the strongbox as well as other

apparatus, including camera mounts, CCD cameras, signal conditioning (S/C) box and

LVDT. The test package was carefully moved to the centrifuge arm and spun up to 42

rpm to check the centrifuge and model response. The centrifuge was then spun up to the

specified test acceleration level at the base of the model keel. After the gouge process, the

centrifuge was decelerated and then stopped. Following inspection and photographs of

the model testbed, the model test package was removed from the centrifuge chan1ber.

4. 7 Particle Image V elocimetry

Particle image velocimetry (PIV) is an image analysis tool that can be used to measure

soil defom1ations with considerable precision. Combined with high-resolution digital

images, PIV software is able to utilize an autocorrelation function and hi-cubic

interpolation to track the movements of patches of pixels between two images and

return deformation measurements to a fraction of a pixel. PIV tracks the movement of

patches of pixels between digital photographs taken from a stationary camera at a set

time interval. Digital images are matrices that provide a brightness value for each pixel.

In a colour photograph a pixel is assigned three brightness values ranging from 0 to

255, one for each of the three colour channels, whereas pixels in a monochromatic

image will be assigned a single brightness value, White et al.(2003). The contrast

between adjacent pixels is proportional to the difference between their respective

38

brightness values. A square patch of pixels is selected from the first image and PlY

searches for it in the second image. The Fast Fourier Transform is applied to the

patches in order to approximate the brightness matrix with a function of sine and cosine

to that the autocorrelation function can be used to compare patches in the two images,

Renawi (2004). The patch location in the second image is shifted about a

predetennined search area and the pixels are compared to the patch in the first image.

The autocmTelation function returns a planar surface that represents the degree of

compatibility between the two patches being compared. These planar surfaces, each

one a square pixel, form the surface shown in Figure 4-6. A distinctive peak in the

figure indicates the location of greatest compatibility between the original patch and

one in the second image, White et al. (2003).

This method can detern1ine the displacement of the patch to a fraction of a pixel by

fitting a bi-cubic interpolation to the very top of the peak returned by the autocorrelation

function as shown in Figure 4-6 The resolution of the bi-cubic interpolation detennines

the resolution of the displacement vector. If the bi-cubic interpolation is evaluated at

th 1/200 of a pixel, the displacement vector will have a resolution of 0.005 pixels. Higher

resolutions require more computing power and other sources of error generally render a

resolution much higher than 0.005 pixels unnecessary, White et al.(2003).

39

.----,-----------------------------·---·---

Rn (s ) 1·01

1

0·99

0·98

0·97

0·96

R, (•)

0·5 Q.0·5

F~ -!_1·0 -2 -2

(~<)

O~..GIIIGnt ~.

·~ 1~ ll.b-piltel pn;ciSIOI"I

Figure 4-6 Autocorrelation function and hi-cubic approximation being used to detennine the displacement of a patch, White et a1.(2003)

40

r-~-----------------------------------------------------~----- -

The centerline of the model was replaced by a viewing window to visualize the subgouge

defmmation accumulation using PIV teclmiques. The photographic reference field used

consists of at least fourteen 6mm diameter black dots shown in Figure 4-7 provided a

reference field of known object-space coordinates while knowing the image and the

object-space locations of each dot, the optimal photogrammetric transformation

parameters can be found. The camera is placed at a distance from the viewing window.

The subgouge deformation movements were tracked through a successive series of

digital images captured by a CCD photographic camera for tests P02 to P06 at about 0.2

frame/sec. For high speed tests, a high speed Phantom can1era was used for tests P07,

P08 and P09 at up to 300 frames/sec. This technique has been used successfully for all

tests.

Figure 4-7 Centrifuge model test of ice gouging with photographic reference field at test

start and end

41

5 EXPERIMENTAL RESULTS

5.1 Introduction

This chapter discusses the experimental results of the behaviour of saturated sand

subjected to ice-gouge loading under drained to undrained conditions. The studied soils

consisted of Alwhite Silica sand #00. Its characteristics were presented in section 4.2. In

the study of the ice-gouge problem where excess pore pressure dissipation will occur

during the dynamic event, it is necessary to increase the model consolidation time so that

it is more compatible with the inetiial time by using a viscous fluid with the same water

density.

A total of seven tests were conducted in the centrifuge, Table 2-1. The parameters are

different between the seven conducted tests. The significance of parameters such as

attack angle a = 15 and 30 degrees, width/depth ratio of 6 up to 13, gouge depth Ds = 0.2

to 2.4m, keel speed from 0.5 to 55 mm/sec and soil conditions were examined. Two tests

P05 and P08 were included for comparisons to previous Delft Hydraulics flume medium

scale gouge tests, table A 4. Three tests PO?, P08 and P09 were conducted with a faster

gouge rates using a viscous pore fluid. All the first six tests were conducted using a keel

with an attack angle of 30° however the attack angle for the last test, P09 was using the

model ice keel with attack angle of 15°.

42

Centrifuge tests were performed at different centrifugal accelerations on scaled pore

fluid-saturated models as shown in Table 2-1. Responses such as vertical and horizontal

loads, particle deformations, and pore pressure (in test P09) were examined throughout

the tests. The Particle Image Velocimetry (PIV) technique was used to track small

patches of soil texture through a successive series of digital images captured by a CCD

photographic camera for tests P02 to P06 at about 5 second intervals (0.2 frame/sec) or

high speed Phantom camera when required for high speed tests P07, P08 and P09 at up to

300 frame/sec.

5.2 Experimental Load Data Analysis

The centerline of the model was replaced by a viewing window to visualize the sub gouge

deformation accumulation. The test were using an aluminum half width ice keel. For

measuring half model vertical load, three load sells as shown in Figure 5-1 below were

used to link the caniage and the model ice keel. The vertical load is obtained by adding

the data from the three individual load cells. The vetiical load versus keel displacement

are shown in Figure 5-2 to Figure 5-8 which show that the three load sells have different

vertical loads. The far load cell usually has higher readings than the other load cells

which is due to excess surcharge load from the lateral soil mound formed near the far

cell. The maximum vertical load expressed in prototype scale varies from 0.14 KN to

65.2 KN.

43

Viewing Wmdo

Ftontload c

0

Ice keel

modd+~

0

Close load 0

Far load c

Top view

n

Side view

Figure 5-l Top view and side view of vertical Load Cells anangement

n

Model keel

Vertical and horizontal forces data were acquired during the gouging event. Figure 5-2 to

Figure 5-8 shows the model half forces with keel movement for all tests. It may be

observed from all test data that both horizontal and vertical loads increased rapidly as the

keel started to move until a cyclic steady state condition develops. The keel resistance

developed a steady state after about I 00-150mm of keel model displacement in all tests,

Figure 5-9 to Figure 5-15. The gouge force increases are associated with the growth of

the frontal benn. Figure 5-15 shows an example of gouge forces for P09. The anows are

the selected keel position in Figure 5-30 to Figure 5-32 showing the development of the

frontal benn. The frame number versus keel displacement is presented from Figure A. 30

to Figure A. 36. Table 5-1 shows prototype maximum loads at steady state conditions for

all seven tests. The steady state prototype gouging horizontal forces were in the range of

44

.---------------------------~----

7.7 MN to 47.0 MN except for the two shallow gougeing tests P05 and P08 that showed

much less forces, Table 5-1.

The horizontal load and vertical load versus keel displacement for each gouge event

presented in Figure 5-9 to Figure 5-15 show that the cyclic variation present in vertical

load is also apparent in the horizontal load at the same displacement. The total vertical

load represents the summation of the three load cells attached to the model ice keel and

carriage.

Figure A. 1 to Figure A. 6 in Appendix A show the ratio between vertical load and

horizontal load for each gouge event. The ratio is from 1.15 to 1.5 during steady state

(after about 100-150 mm of keel model displacement in all tests) for the entire tests

except dense dry sand test P02 which ratio between ve1iical load and horizontal load is

3.15.

Table 5-1 Sand test results in prototype parameters

Test Attack W/Ds Speed Maximum Fv, Maximum Fh, Average

I. D. angle, (mm/sec) MN during MN during Fv/Fh during

a (deg) steady state steady state steady state

P02 30 7.6 0.5 25.3 8.0 3.15

P03 30 7.0 0.5 9.9 7.7 1.28

P05 30 12 1.1 0.14 0.095 1.5

P06 30 6.25 1.1 65.2 47.0 1.39

P07 30 5.96 5.5 52.5 45.4 1.28

P08 30 11.3 54.6 0.45 0.32 1.3

P09 15 13.3 56.8 32.4 28.2 1.15

45

1.8

1.6

1.4

1.2 z ~

-o .9 5 € "'

0.8

> Qi 0.6

~ 0.4

0.2

50 100 150 200 250 300 350 Model Displacement, mm

Figure 5-2 Model vertical load versus ice keel displacement for test P02

0.8 z ~

-o ~

...J 0.6

5 €

"' > 0.4 Qi

'8 ::;

50 150 200 250 350 400 Model Displacement, mm


46

.--,-------------------------------------------·-

%~--11~~~~~~~~~~~30~0----~40~0----~50~0~---~600 Model Displacement, mm


i _ . ..--'\ ' ' ' ' )"'"'

2.5 · · ··••••· - LC(far) -----~----------------~---------------~----------------~----------7~:~ .............. . LC front : : ,:,--\ ~- : : : : /_,,.,-'- : \_.,. ..... --- : :

2 --------------1----------------[/ ::-·''>T.-.-+ L----------1----------------r---------------1---------------~ : r1 : : : : ~ 1.5 .............. ~--------/--f--·-----·-------i----------------i----------------f--------·------~--------- .... . T§ i I i i i i : ! 1 ---------- --·+-/---- ------f-------- -- ---- --~-- -- ---- -- ----·; .. .. ....... .l.. ....... ----+-------------~ : rl--- :........_..., "-- : - r- .,_ - ...,_ :.--- ...;. " -.., ..::: :I ! : l ; :

,: •••• --•-- r -•• -••••• r--•--r•- ••• r ~ ••••• ••J-500 600


47

3.5.---------,------.---------,------.-------,-----,

z ~

.,;

2.5

g) 2 _J

B 'e ~ 1.5 a;

~

100 200 300 400 500 Model Displacement, mm


50 100 150 200 250 300 450 Model Displacement, mm


48

50 100 150 200 250 300 350 400 450 Model Displacement, mm


5,---,-----------.-----------.----------.-----------,----------~

z ~

3.5

"' 3 ~ 0

~ 2.5 o; I a; 2

~ 1.5

' ' '

.: •·• F i r•• ··••••••·•· i••····•• •···· :················ oL---1~oo-----------1~so ___________ 2ooL----------2~s-o--------~3~oo~--------~3so

Model keel movement, mm

Figure 5-9 Model total vertical and horizontal loads versus ice keel displacement for test P02

49

1.6

1.4

z 1.2 ~ .,;

~ 1 ~

~ 0.8 a;

~ 0.6 I I I I I

-- ------- -r------- ----:-------------r-----------r-----------r------------r-----------·-r·---------

. · ···-:::- T , ••••••••••r••••••J·••••••• I ••••••••• I••••••• 50 100 150 200 250 400

Model keel movement. mm

Figure 5-l 0 Model total vertical and horizontal loads versus ice keel di placement for test

z 0.4 ~

P03

' ' ' ' -- -·-- --------------- ... ·------------------~- - ---.

' ' ' ' '

-------------r·---------------r·--------------r----- -------r·---------------r----------------

100 200 300 400 500 600 Model keel movement, mm


50

I I o 0

' -- - --- ----:------- - +--- - ' :---------- •

~ 4 -----------------1-- ----------------r----- ------------ ;------ -----------:-------- --------:-----------------

uf : :

~ ' ' ~ 3 ----- ~-- ------------ ----~--- ---------------- ~--- --------------- ~---- --------- ___ ._ ---- --------- ----m : : I

I i i ' '

-- ---------- ---1·-----------------r-----------------·t··----------------:-----------!-----·-r··---------------

, - • --- +------------------·----------- · ---- ---- ---7---------------

%~------~,o~o--------~2o~o~------~3~oo~------~4Loo~------~5Loo~------~6oo Model keel movement, mm


4.5.---------,----------.----------,----------,.-----------,--------, I I I I I

.••• ±:• t·: ---;- ::·: :::::·:-·::·:;: : : :r::-:: ::::r: :: I -----·-----·----1-------------------~--------------------t-------------------1-----------

i i i i '---.....:...=:;.:=::........~ 1 ---------------··t· -------------------~--------- -----------t ---- ----- ---------- i---------------_____ ! ____ --------

1 0 I I I I

0.5 '··················j···················t···················f···················(····· ············-(·········· 100 200 300 400 500

Model keel movement. mm


51

w---.-----------------------------------

100 150 200 250 400 Model keel movement. mm


P08

' : '--•: ..:.Ve"'rt_,ic::::a:...l _,

I I I I I I I I

2.5 ·--·--·····r·-··-·--···-r·-·········r··-··-·-··r··-····-·1········-··-~~::·-··-······

·-·-····--·~---··---·-·-~·-·;~~-<=~:[: ····-···-- ~ ·-·---··-- .;. ·······--z 2 ll:: ! ~~~ : : i 1 1 l

i / i i i i i i i ---------rc----- . ----------;------------~-- ---------~------------~ -----------t------------t-----------. 175mm 307nun : :

. ' ' I I I I I I I I T T T - ",--- < -~ T T o.s ·-- ·--·-T·-·--····T·-----·-·T·-·---··--:--·-·-·-···T···-·-··-r···-··--·r·····---·r····---··

50 100 150 400 450 Model keel movement, mm


52

5.3 Subgouge Deformation

The subgouge defonnations of a senes of even centrifuge tests were tracked using

Particle Image Velocimetry (PIV technique ) adopted by White et al. (2003). The PIV

technique can track well as low as 0.2mm displacements below the keel. As the model ice

keel is driven in the sand, the soil reaction force increase and cause the development of a

deep seated bearing failure mechanism. As the keel advances, this mechanism is

overridden and the load decrease corresponds with the clearing proce . This cyclic

process continue with continued displacement. These load cycle ha e been correlated in

all te ts to the failure mechanism.

Figure 5-16 bows the forces and maximum horizontal defonnation with keel movement.

The maximum horizontal deformation is also een to be cyclic in nature. The peaks in the

horizontal deformation curve (A' B') corre pond to the peaks in the load curve (A, B)

with a 120mm geometric offset which means that the maximum horizontal deformations

are 120mm ahead of the ba al comer of the keel where load resistance were measured. (

A maxima in forces associated A' maximum in GO accumulation). Figure 5-30 to

Figure 5-32 show the clear three failure urface at different stage of keel mo ement for

te t P09. Figure 5-18 to Figure 5-29 shows some of the selected ubgouge deformation

fields for the other conducted tests. The units are in mm, and the defonnation vectors are

magnified by 10-20.

Figure 5-33 to Figure 5-39 show the maximum horizontal subgouge displacement at

different keel positions. Comparing Figure 5-33 to Figure 5-39, the maximum horizontal

53

.-----:--------------------------------------- ----------

subgouge defonnation usually appears under the final position of the keel base. Figure

5-40 to Figure 5-46 present the form of the subgouge displacement. The distance x

represent the distance from the right side of the box to the keel. Large displacements

occurred at the base of the keel decreasing with depth.

Figure 5-16 Forces and horizontal defonnation accumulation with keel movement for P08

100

120

uo

160

180

200

220

240 120 mm

Figure 5-17 Tyoical SGD accumulation ahead ofbasal keel corner

54

P02-Frame-2-14.mag20 100r-----------r-----------r----------,,---------~~---------.-----------.-----------.---

150

200

250

' ' ' 300 ' ' ' \ ' ' -

\ \ ' ' \

\ ' - ' ' \ ' ' \ ' ' ' ' ... -- \ \

\ \ \ \

~250~--------~300~--------~~~---------~~----------.~50~---------~~--------~.~50~--------~~~~

Figure 5-18 PIV subgouge deformation for frame 2-14, displacement of 67.5 mm, Magnification xlO, P02

100

180

200

220

240

200

280

300

320

340 ~

\ " \

~ 450

\ \ ' ' ' \ \

:;- ...... ~ ., . --- ..

\ ' - ' ' ...

' \ ' ' ' \

~ 550 ~

Figure 5-19 PIV subgouge deformation for frame 26-32, displacement of 154.2 mm, Magnification x 10, P02

55

150,~----.-------,-----,.---P0-2.f•..,.........,....; .. :._'o ___ ~----~- -----.-

200

300

~L----~---_i ____ L_ ___ ~ ___ _i ____ L_ ___ _L_J

~ 300 ~ ~ ~ ~ ~ ~

Figure 5-20 PN subgouge deformation for frame 34-36 displacement of 173.5 mm Magnification x 10 P02

~------.---~---~--PO-~---~~-~~ __ ,o_,.-----~r---~ ,-- -----.-.

150

200

250

' I I \ ' I ' 300 ' . I ' I ' . .

' ' I

' ' ' '

~ 200 250 300 350 ~ ... ~ 050 ~

Figure 5-21 PlY subgouge defom1ation for frame 6-18, displacement of93.6 mm, Magnification xI 0, P03

56

P03·bme27·38-m-o iO 100,-----.------.------.------.------.-----~------~------~

150

200

2$0

300

Figure 5-22 PIV subgouge defonnation for frame 27-36, displacement of 187.2 mm,

Magnification x 1 0, P03

100

200

250

Figure 5-23 PIV subgouge deformation for frame 11-12, displacement of 198 mm Magnification x20, P05

57

~--------.--------.--

100

200

,•

200

Figure 5-24 PIV sub gouge deformation for frame 19-21 , displacement of 346.5 mm, Magnification x20, P05

1 ..

.. 100

120

--~-........ ..-....

...,..-,...,...,...,._.,, _,.,,.. //.;-

_.,._.,.,..

250 300 •so

Figure 5-25 PIV subgouge deformation for frame 19-21 , displacement of 178.1 mm, Magnification x20, P06

58

eo

100

'"' ,..

200 ~ ' .. • • • • • •

220 ... - .... - '

24(1 ·~ : =~:::: · ~: · : ·

300

Figure 5-26 PlY subgouge deformation for frame 24-31, displacement of262.9 mm, Magnification x20, P06

' ' - .... · ...

400 ... 500 550 000

Figure 5-27 PlY subgouge deformation for frame 7-9, displacement of246.9 mm, Magnification x 10, PO?

59

00

80

100

120

... 100

100

200

220

,.. 200

300 ,.. ... . ..

Figure 5-28 PlY subgouge defonnation for frame 10-13, displacement of356.7 mm, Magnification x 10, P07

200

300 .

~L-------~------_L ________ L_ ______ ~ ______ _L __

~ 200 ~ 300 ~ - ... 500

Figure 5-29 PIV subgouge defom1ation for frame 35-46, displacement of209.9 mm, Magnification x 1 0, P08

60

P®-Fr•me 2&-37.m-v10 100

120

140

1 ..

100

200

220

240

,..

2eo

300 150 200 250 300 350 400 450

Figure 5-30 PlY subgouge defonnation for frame 28-37, displacement of 175 mm, Magnification x 10, P09

POO-Fr~me37-"15-mag10

100,--,-------,,-------.-------,----~-.-------,~------.-------~

150

200

'' ' ... ,,,,,,, ............................... ~. 250

300

150 200 250 300 350 400 450 500

Figure 5-31 PlY sub gouge deformation for frame 3 7-45, displacement of 212.8 mm, Magnification x 10, P09

61

P®-FAime~

100r-----------.-----------.-----------.-----------.-----------.-----------.-----------.-.

1150

2150

300

, , , ,

' I I

'I

, , ,. .. , .. . , " .. . ~ ,. , , , , ,

Figure 5-32 PN subgouge deformation for frame 53-65, displacement of307.4 mm, Magnification x20, P09

Horizontal movement Profile below keel elevation for Test P02 X (mm) and horizontal displacemnt, mm (scale 1:1)

X (mm) and horizontal displacemnt, mm

~~~~~~~~~~~~-~m~~~~mm

.

' ' ' ' '

____ ., _____ ., _____ ,_ ____ ., ____ _

' ' . ' . . . ' . ' . . . __ __ ,... ___ __ .. _____ ... _ . . . . ' . . . ' . . ' . . ' . . . . . ' . ' ' . . ' . . . ____ ... _____ .. _____ .. __ -. ' ' . . . . . . . . . . ' . ' . . ' . . ' . . . ' . . ' . ____ _, _____ .~ _____ .. __ . . . . ' . . . . . ' . . . . . ' . . . . ' . . . ' . . ' . ____ .... _____ J _____ .. __ _ . . . ' . ' ' . . ' ' . . . ' ' . ' ' . ' . ' . . ' . . ' . + + +

140

150

160

170

'E .s >-

180

190

200

Figure 5-33 Horizontal movement profile below keel elevation for test P02

62

Horizontal movement Profile below keel base for Test P03

X (mm) and horizontal displacemnt, mm (scale 5:1)

520 500 480 460 440 420 400 380 360 340 320 300 280 260 240 220 rr~~~~----r-~~~.-~-r~~~~~----r-~~~~~~-r,~~~-. 210

' I I I I I I I I I I I I I -:------r-----r ----·r·-- ------:-------1-------:------1------r------:-------r------r------r -------r-----~~~~--+-~~~

' ' I I I I I I I I I _.,. ______ ---- - ------ -t---- ---· ---- ...... ------~ -------..-- ----- _______ .,. ------1 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I + I I I I I I I I t I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

; l : : i : : i l l

220

230

'E .s >-

240

250

LL'--~'--~!----~·--~--~~----!~--~·--~~--~!~--~:--~--~----L---~~ 260

Figure 5-34 H01izontal movement profile below keel elevation for test P03

Horizontal movement Profile below keel elevation for Test P05


690 670 650 630 610 590 570 550 530 510 490 470 450 430 410 390 370

'

' ' I I I I I I I I I I I I I I ------r------ t ------ , ------ , ------ , ------ , ------, ------, ------.,--- ---r ------r ------r-------r------,.------, ----- 150 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

: I : : : : , : I : : +- +- ~ : : I

! l : i ;, l I l ' l l i l : ______ } _____ : ______ i-- - : ------~-- -- ~-\--- ~------~ -----: --- --~------~-----~--- -- ~------~-- -- : ---

: : : : : : : : : : : ' : : : I I I I I I ~ I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I t I I I I I 1... I I

160

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64



560 540 520 500 480 460 440 420 400 380 360 340 320 300 280 260 240 220 200 180 160 140 120

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Figure 5-40 Subgouge horizontal displacement for P02

Model Horizontal Displacement POJ, mm

0 8 12 16

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Figure 5-44 Subgouge h01izontal displacement for P07


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68


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5.4 Gouge Form and Mound

Before each centrifuge test, a soil mound was placed in front of the model ice keel to

reduce the require gouge length required to reach the steady state. When the keel is

moving in the sand, sand accumulates to the side of the keel and in front of the keel. After

the keel has passed, some of the sand mound at the side of the keel falls down back into

the gouge path, so the gouge width will be smaller than the width of the keel. As the keel

is moving in the sand, the mound will increase in height until reaching its maximum

height . Figure 5-47 and Figure 5-48 show the side view and the top view of the gouge for

P05 and P06 as an example. The other top and side views ofthe gouge are in Figure A.21

to Figure A.27. Figure 5-49 to Figure 5-53 show the measured dimension of the gouge

and the mound in front of the keel at the end of the test

69

Figure 5-47 Side view of gouge shape for test P05

Figure 5-48 Top view of gouge shape for test P06

70

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Figure 5-49 Top view of gouge shape and dimension for test P03

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Figure 5-5 I Top view of gouge shape and dimension for te t P06

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75

6 ANALYSIS

6.1 Introduction

A total of seven tests were conduced. For the seven tests, all the parameters and both

horizontal and vertical forces that were measured from the centrifuge tests are shown in

Table 6-1 . The parameters were different between the seven tests. A 30 degrees attack

angle for the model ice keel was used for tests, P02 through to P08. A 15 degrees attack

angle for the model ice keel was used for test P09. The gouge depth ranged from 0.18 m

to 2.4 m in prototype te1ms for the seven tests; P05 and P08 had the smallest gouge

depth. The keel speed ranged from 0.5 to 55 mm/s.

Table 6-1 Sand test results for vertical and horizontal loads in prototype parameters

Gouge P02 P03 P05 P06 P07 P08 P09

Angle( degrees) 30 30 30 30 30 30 15

Depth(m) 1.3 1.43 0.18 2.3 2.4 0.19 1.2

Width(m) 10 10 2.2 14.4 14.4 2.2 16

Dr 93.6 51.5 58 50.8 39 68.1 38.6

Fv(MN) 25.3 9.9 0.14 65.2 52.5 0.45 32.4

Fh(MN) 8 7.7 0.095 47 45.4 0.32 28.2

Fv/Fh Ratio 3.15 1.28 1.5 1.39 1.28 1.3 1.15

Speed (mm/s) 0.5 0.5 1.1 1.1 5.5 54.6 56.8

Mound height(m) 3.38 2.145 0.648 3.749 4.032 0.739 3.132

Combined height(m) 4.68 3.575 0.828 6.049 6.432 0.929 4.332

76

.----,----------------------~----------·--------~

P02 was conducted in dry dense sand and P03 was in water saturated medium density

sand. These two tests were aimed at proving the equipment and techniques. Tests PO?,

P08 and P09 were conducted with a fast gouge rate using a 30 est viscous pore fluid to

retard excess pore pressure dissipation. The subgouge deformation was determined by a

PIV analysis for all PIRAM tests. All the defonnation for different layers below keel is

determined with the largest horizontal defonnation of the layer in the period.

6.2 Vertical Settlement during Centrifuge Test

During the spin up of the centrifuge test, the model sand will be compressed by the

acceleration level acting on the model, thus reducing the soil depth, which means that the

gouge depth and the density of the model sand will change during the centrifuge spin up.

For this reason, L VDT'S are necessary for measuring the exact settlement during the

centrifuge test (Figure A. 14 to Figure A. 20).

Table 6-2 presents the settlement of model sand during sand preparation and centrifuge

testing which shows that usually the settlement of model sand will increase when the g

level is higher or the density is lower.

77

Table 6-2 Model sand settlement during preparing and centrifuge testing

Test Original Density Settlement Settlement Density Actual Ds G

I. D. Ds after during during during during level

(mm) sand saturation centrifuge centrifuge centrifuge 0 0

and loading spin up test (kg/m3) test (mm) rammg

(kg/m3) (mm)

' (mm)

P02 25 1587 1.3 1592 23.7 55.6

P03 29 1443 1.0 2.2 1457 25.7 55.6

P05 17 1470 1.3 0.7 1481 15.0 12.2

P06 33.5 1432 2.8 1.9 1455 28.8 80.0

P07 35.4 1396 2.6 2.6 1421 30.2 80.0

P08 17.2 1502 0.6 0.6 1507 15.9 12.2

P09 21.5 1397 2.0 4.4 1420 15.1 80.0

6.3 Frontal Berm

In all tests it was observed that the height of the bem1 which is measured from the ground

surface to the top of the sand mound increases with the keel moving fmward until it

reaches a maximum height as the keel reaches the end of the test position. The frontal

be1m height has a significant effect on the force and subgouge defonnation. Kappa value

was introduced to describe the frontal berm height. Kappa value is the frontal benn height

as multiple of gouge depth as shown in Figure 6-1. Table 6-3 is shown the Kappa value

that estimated when the height of the berm is reaching the maximum level.

"""----K-ee-1--B-ea_~ ... ~~=~------~~~~~:I:~_:_s s

Figure 6-1 Frontal berm height as multiple of gouge depth, k

78

Because of the limit space In the box, the keel displacement was limited. There was an

initial berm made for each test during preparation to reduce the distance required for the

frontal berm reaching the steady state. The benn grows until reaching steady state

condition. The growth of the benn is also associated with the growth of the gouge force.

Figure 6-2 is the comparison of the kappa value from the three different test programs.

The kappa value seems to increase with the increasing of the attack angle of the ice keel

for all the tests. There are other differences between the three programs which may cause

the differences in kappa value between programs. Test P02 which is in dry sand is not

included in the plot.

Table 6-3 Sand test results and kappa value in prototype parameters

Test Attack W/Ds Speed Kappa Maximum Maximum Average

I. D. angle, (mm/sec) Fv, MN Fh, MN Fv/Fh

a (deg) during dming during

steady steady state steady state

state

P02 30 7.6 0.5 2.6 25.3 8.0 3.15

P03 30 7.0 0.5 1.5 9.9 7.7 .

1.28

P05 30 12 1.1 3.6 0.14 0.095 1.5

P06 30 6.25 1.1 1.63 65.2 47.0 1.39

P07 30 5.96 5.5 1.68 52.5 45.4 1.28

P08 30 11.3 54.6 3.89 0.45 0.32 1.3

P09 15 13.3 56.8 2.61 32.4 28.2 1.15

79

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Kappa Value from Different Tests

•

10 15 20 25 30

Aspect Ratio, W/ Ds

35

• DH Flum r unl 15

• • DH Flume run2 30

40

DH Flume run3 15

x DH Flume run4 45

X PIRAM 30

• PEISE 15 degr

+ PIUSE 30 degree

- DH Flume r un4 45

- DH Flume run2 30'

- DH Fl ume runJ 15

- DH Flume run3 15

- PlRAM 30

- PRISE 15 d gree

- PRISE 30 degree

Figure 6-2 Kappa value from different test program

Kappa Value Variation with Keel Aspect Ratio for PI RAM and PRISE tests

•

•

5 10 15

Aspect Ratio, W IDs

20 25 30

+ P02

• P03 P05

X P06

:.:: P07

e P08

+ P09

· PRISE 15 degr e

- PRISE 30 degr~e

Figure 6-3 Kappa value versus aspect ratio for PIRAM and PRISE tests

80

.----,-----------------------------

Figure 6-3 is the plot of kappa value versus aspect ratio for PRISE and PIRAM tests

which have the larger gouge depth. It indicated that the frontal berm height normalized by

gouge depth linearly corresponds with the aspect ratio. The relationship between kappa

value and aspect ratio can be expressed as kappa=W /5Ds. P02, P05 and P08 are

significant outliers. P02 was conducted in dry sand; P05 and P08 had smaller gouge

depth. Figure 6-3 indicated that there is no significant effect for kappa value between 15

degree and 30 degree for deep gouge depth.

6.4 Bearing Pressure

Bearing pressure is the nonnal bearing force on the face over a bearing area which is the

inclined keel face including the frontal bem1. For the bearing pressure, crb, C-CORE

(2008) developed an empirical equation for bearing pressure as crb(MPa) = 0.09 Ds (m)l.5

as shown in Figure 6-4 C-CORE (2009b ). Figure 6-5 shows the beming pressure at steady

state for PIRAM test and the empirical equation line. It can be seen from the figure that

the PIRAM tests are capture well with the empirical equation line. P02, P05 and P08 are

higher than the empirical equation line. This may because of an increased soil dilation

under lower effective stress and the reduced soil self weight which decrease the gouge

resistance in these 3 tests. The reason of the discrepancy between P06 and empirical

equation line is unknown.

81

0.8

~ ~ PR3cPR • Paul.1

0.7 crb(MPa) = 0.09 Ds m) 15 V' PRSA01 0 Paul.2 .&. PRSA02 • Paul.3

0.6 <t] PRSA03 + Paul.4

~ PRSA04 ... Poor.2c

~ * PRSA05 13 Poor.2t :E 0.5 q Site 1

~ 0 Site 2 :::J • Site 3 Cl)

0.4 ~ G> Site 4 a.

~ PR018-2 ~ ~

·~ 0 3 *[;> 0 PR01C-1 m . PR01C-2

m A PR09-1

0.2 q PR09-2 '7 PR10-1

0.1 • PR10-2

0 0 1 2 3 4 5

Gouge depth: Ds, m

Figure 6-4 Keel bearing pressure on gouge and benn surcharge C-CORE (2009b)

0. 50

o. 4o X

• 1'02 0. 40

0. 35

,£.

~- 0. 30 1'05

" v:

"' " 0. 25 .... X 1'06

"-.. " .... 0. 20 g

* 1'07

0. 15 • POll

(), 10 + 1'09

0. 05

0. 00 () 0. 5 1. 5 2. 5

Gouge Depth , lls

Figure 6-5 Bearing pre ure versus gouge depth

82

6.5 Gouge Force Variation

6.5.1 Gouge Force with Aspect Ratio

The sand test results for vertical and hmizontal loads in prototype parameters are shown

in Table 6-5. As the frontal berm grows, the gouge force increases with keel displacement

until it reaches a cyclic steady state which explained in section 5.3. Figure 6-6 shows the

force per unit width versus the combined gouge depth which shows clear tendency that

the force increase with the increasing of the combined depth.

Horizontal Force Variation for Prototype

~.5 .-----------------------------------------------------.

X

• P02 • P03

P05 + X P06

X P07

• •

• 0 ~----~------~-------L------~------~------~----~

0 :l 5

combined depth,D ( l+k)

Figure 6-6 Prototype horizontal force per unit width versus combined depth

Figure 6-7 C-CORE(2009) is the model test horizontal gouge force normalization versus

the aspect ratio. The data plotted in the figure contains PIRAM test, PRISE test Phase 3a

and Phase 3c, Memorial University 1 g test and Site test (Table A 1 ). The combined

83

depth trend line is considered by normalizing force per width by the square of the

combined depth and the submerged unit weight of the sand. There are four groups of data

in Figure 6-7. One comprises 7 shallow gouge tests which are P05, P08 and Memorial 1 g

tests. The second group contains P02 and P1 0. P02 is conducted in dry sand and PI 0 is

using a double-keel. The other two groups are for deeper gouge depth greater than 0.3m

with attack angle of 15 and 30 degrees.

40

• P02 ~ Site 1 @ P03 • Site 2

35 P05 Site 3 .. • • P06 ,. Site 4

30 • P07 .. Paulin 1

• P08 , . Paulin 2

N ~ P09 • Paulin 3 li) 25 Kappa= W /50 P10 ,. Paulin 4 ~ ~ PR01B-2 ~ Poor 2a + 0

~ 4 PR01C-1 Itt Poor 2b !f 20 (l =15° ~ PR01C-2

E ~ i PR09-1 Q a =3Qo ro

Ol ~ te PR09-2 :c 15 '•

LL .. @ PR10-1

--~ . ~ PR10-2 10

Fh /y W (D5+W/5 'f = • PRSA01 0 ·· .. •. . (7 sina -5).(15-W/0

5)/15 +5 ~ PRSA02 · :!

5 ..

~ PRSA03

a =30° () 0

.,.. PRSA04 ~ PRSA05

0 0 5 10 15 20 25 30

WID

Figure 6-7 Horizontal gouge force normalisation C-CORE(2009b)

An empirical relation was fitted to these two groups of data. These empirical relations

are compared with the analytical solution of Walter and Phillips (1998) with the PRISE

JIP for sand with a submerged unit weight of 10 KN/m3 and gouge depth of 0.2, 0.5, 1.0,

2.0 and 3.0m. The peak and critical state friction angles are 37 and 35 degrees in Figure

84

6-8. The empirical relation ts consistent with the analytical force model where the

empirical relation is:

0

..,

0

F11 I y'W (Ds+W 15l = (7sin a -5)(15-W 10 5)115 +5

= 5

.,. +

+ • •

~ ... + • ... + +

• +

0 0

0 0

0 ! 0

a o 0 ! o o

co D 0 - I D

for WID 5<15 , and

for WIDs >15

.... ~30 4..,....

D

Figure 6-8 Lateral gouge force comparison of empirical and analytical functions

6.5.2 Force Ratio

As shown in Figure 6-9, all the tests that used saturated sand are in a natTOW area which

can be expressed as Fv1F11 = 1.15 to 1.5. P02 is a dry sand test with a force ratio to aspect

ratio of 3.15. This higher ratio for P02 may because it does not have excess pore

pressures and water resistance for horizontal force. It may also because of the lack of

buoyancy force in vertical force. From P03 to P08 with an attack angle of 30 degrees, the

85

S)

force ratio to aspect ratio is 1.28 to 1.5 with an average of 1.39. The force ratio to aspect

ratio for P09 is 1.15, which is the lowest, as the attack angle is 15 degrees.

0 3. 5 ~ = I. 3 QJ u I. 2. 5 .£ -;

2 ..... c 0

,t:j I. 1. 5 0 .c 0 ..... 1 -; u 0. 5 t: QJ

~

0 '0

3. 5

E 2. s

j l 2

] 1. 5 g ] ·~ 1

0. 5

0 0

--

•

• X • • X

2 4 6 8 10 12

Aspect ratio, W/Ds

Figure 6-9 Prototype force ratio to the aspect ratio

•

)( • • " ....... --- - - -- - : -

,

10 Iii 20 25

Aspect ratio, W/ Ds

• p02

• p03

p05

X p06

X p07 + • p08

+ p09

14

• p02

• p03

,>Os )( p06

" p07 • pO + p09

- i>RI E

MUN l g

30

Figure 6-1 0 Comparing force ratio to the aspect ratio with PRISE and MUN 1 g test 1990

86

Compared with the PRISE centrifuge sand test and Memorial University 1 g Physical

Model Sand Test, Figure 6-10, the average force ratio of test P03 through to P09 is higher

than the average force ratio of the PRISE test and the MUN test. All the data are plotted

in a narrow area in Figure 6-1 0, which indicated that there is no effect of the aspect ratio

on the force ratio and the attack angle. The high density dry sand test, P02 shows about

double force ratio that for other tests.

6.6 Comparison with Medium Scale Tests

Table 6-4 <?Ompares the Delft Hydraulic (DH) flume tests, Vershinin et al. (2007), with

PIRAM tests P05 and P08. The gouge depths of the DH tests are around 0.2m which is

shallower than most of the PIRAM and PRISE tests. Comparing P05, P08 and DH Run2

tests, the attack angle are all 30 degrees. All equivalent gouge depths and widths are the

same. The DH tests were in water saturated fine sand. P05 and P08 used the viscous fluid.

Figure 6-11 is the comparison of the maximum horizontal deformation for prototype

between P05, P08 and DH Run2 tests. Although the subgouge defonnations have the

consisten.t · shape, P05 and P08 have a deeper extent. This difference may be partly

because of the smaller ice keel displacement which means DH Run2 tests may not reach

the steady state and the limit of 9 gouge depths of sand below the keel in DH tests.

87

Table 6-4 Comparison of the DH test Run 2 and PIRAM test P05 and P08

Attack Gouge Gouge Bearing Max SGD

Test J.D. angle, Dr% Depth, Width, Speed,

F) Fh kappa SGD pressure extent mm/sec

a (deg) Ds (m) W(m) kPa m 111

Run 2 -1 30 55 0.19 2.2 13 1.39 1.55 64 0.02 0.4

Run 2 -2 30 55 0.19 2.2 12 1.27 2.51 75 0 .085 0.25

Run 2 -3 30 65 0.19 2.2 20 1.45 2.85 147 0.03 0.25

P05 30 58 0.18 2.2 1.1 1.5 3.6 46 0.07 0.7

P08 30 68.1 0.19 2.2 55 1.3 3.89 123 0.08 0.7

Figure 6-12 shows· the forces ratio versu the combined depth. The depth values increased

during the 3 stages of the DH Run2 tests which indicated that the frontal mound were

accumulated during the 3 stages of the DH Run2 tests. It means that steady state

conditions were not achieved in each DH tests step which can explain the lower subgouge

defonnation than P05 and P08. PIRAM tests have a significant initial frontal benn before

gouging and have higher gouge length to depth ratios.

88

-0.0 1 0.01

subgouge horizontal deformation, m

0.03 0.05 0,07 0.09 0. 11

P05

-- P08 -+- DH Run2 test I

--- DH Run2 test2 ""*'- DH Run2 test3

0. 13

Figure 6-11 Horizontal subgouge deformation ofthe DH test Run 2 and PIRAM test P05 and P08

2

1.8

1.6

1.4 ::K •

X • 1.2

0. 6

0.1

0. 2

0 L_ __ _L ____ L_ __ _L ____ L_ __ -L----~--~----~--~-----

0 0. I 0.2 0. 3 0. 1 0. 5 0. 6 0. 7 0.8 0.9

Combined Depth, Ds(I+k)

+ p05

• pOs A Dl-1 Run2 test I

X Dl-1 Run2 test2

::K Dl-1 Run2 test3

Figure 6-12 Force ratios ofthe DH test Run 2 and PlRAM test P05 and P08

89

0. 2

0. 18

E .._ 0. 16 z:

:; £ 0. 11 -"0

:i 0. 12 . ..: = ::s 0. I ~ u ... 0 0.08 "'" -; - 0. 06 = 0 N *i: 0 0. 04 :c

0.02

0

•

0 0. 1 0.2 0.3 0.4 0.5 0. 6 0. 7 0.8 0.9

Combined Depth, Os(l+k)

• 1'05

• 1'08

.A. DH Run2 test I

X DH Run2 tcst2

::1:: Dll Run2 test3

- Fh/w=O.I(Ds( l +k)Y2

Figure 6-13 Gouge force per unit width versus combined depth between DH Run2 and PIRAM tests POS and P08

to.l ..... 'iJ: g. 0.2

] ~ 0.3 0

0 .D

8 0.4 t:

"' t5 :0 0.5 ] ·~ 0.6 > -o .~ 0.7 (;i

E 0 0.8 t:

0.9

0.02

normalised ubgouge horizontal deformation,Ds(J+k)

0.04 0.06 0.08 0.1 0.12

P05

--- P08 -- DH Run2 test I -+- DH Run2 test2

--*- DH Run2 test3

0 .14

Figure 6-14 Normalized horizontal subgouge deformation of the DH ~un 2 and PIRAM

test POS and P08

90

Figure 6-13 is the gouge force per unit width versus the combined depth which shows

that the combined depths have a significant influence on the gouge force . The horizontal

gouge force seems to im~rease with combined depth squared. As the combined depth is an

important parameter in assessing the gouge force and the subgouge defonnation. Figure

6-14 is the normalized horizontal subgouge defom1ation by combined depth between DH

Run2 tests and PIRAM tests P05 and P08. It shows that the subgouge defonnations have

the consistent profile. The vertical extent for both PIRAM tests and DH Run2 tests are up

to 0.8 as the ve1iical extent is related to the combined depth.

6.7 Subgouge Deformation

Figure 6-15 shows the maximum horizontal subgouge deformation profile of all the

PIRAM tests. Figure 6-16 is the maximum horizontal subgouge defom1ation profile in

prototype. Figure 6-17 is the subgouge defmmation normalized by the combined depth.

All the three figures shows that the tests have consistent profile. P09 has the larger

horizontal defom1ation because the attack angle is 15 .degree.

Figure 6-18 is the compmison of the nonnalized horizontal subgouge defonnation of

PIRAM tests and PRISE tests. The tests profiles are all consistent. Most of the PIRAM

tests have the attack angle of 30 degree except P09 is 15 degree. Most of the attack angle

of PRISE test is 15 degree. The maximum horizontal subgouge deformation for PRISE

tests is larger than most ofPIRAM tests.

91

r-~---------------------------------------------------------------------------------

e E

ll ,;;;(.

::: 0

Ql J:l

~ c: ~ ..... "' :a

"eij <J

'f Ql ...

0

0

10

20

30

40

50

60

70

80

90

100

0

• • • •

• .. • +

• • X

• + X

• .f' X

.... +

+

+

5

~ .

•

X X

+X

X

subgouge horizontal displacement, mm

• X

• +

10 15 20

II< +

+

25

• P02

• P03 POS

X P06

X P07

• P08

+ P09

30

Figure 6-15 PIRAM model subgouge horizontal displacement profiles

subgouge horizontal deformation, m

0.5 I 1.5 2 2.5

-+- P02

-- r o3

POS

-- ro6

-11- P07

-+- P08

-+- P09

P02

- P03

POS

P06

P07

X P08

P09

Figure 6-16 PIRAM prototype subgouge horizontal displacement profiles

92

nonnalised subgouge horizontal deformation,Ds(l +k)

0.05 0.1 0. 15 0.2 0.25 0.3 0.35 0.4

,....... .!><: + 0.2 'rJ{ 0 8 0.4 .!><:

~ -+- P02

~ 0.6 I--- P03 .0 P05 0 0 ..- p06 ~ 0.8 t; --11- P07 :0 -+- POS co 0 --+- P09

-~ > ] 1.2 -~ "' E 1.4 0 c:

1.6

Figure 6-17 Normalized PIRAM prototype subgouge horizontal displacement profiles

nonnali ed subgougc horizontal deli rmation,Ds( I +K}

-0.05 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

~rL------------------------------------------------~

P02

P03

P05

-+<-- 1'06

- 1'07 --ro --+-P09

- ~- PRSAOI

• PRSA03

PRSA04

- PRSA05

Figure 6-18 Normalized PRISE and PIRAM model subgouge horizontal displacement profiles

93

Phillips et al. (2005) used the relative dilation index, Ir, as an approximate descriptor for

the sand state during the gouging event. The dilation index is defined as:

1,. = D,. ·(10-lnab)-1

where, crb is the bearing pressure in MPa and Dr is the relative density. The vertical extent

of the subgouge deformation, Table 6-5, is related to the combined depth and the soil

state.

Figure 6-19 considers .the vertical extent of sub gouge deformation with dilatancy index, Ir

for previous tests C-CORE (2008). The maximum vertical extent is around a dilation

index of 1. Figure 6-20 C-CORE (2008) is the nom1alized subgouge horizontal

displacement by measured vertical extent with the dilation index. The normalized

displacement value represents the shear strain of the subgouge deformation. It indicated

that the tests with higher attack angle of 30 degree have the lower magnitude of sub gouge

deformation than the tests with 15 degree.

C-CORE(2008) developed the empirical relationship for subgouge deformation from

reduced-scale model tests with unifonn soil condition. The empirical functions are used

to define the magnitude and spatial extent of subgouge deformation. The subgouge

relationship parameters are shown in Table 6-6. Equations 6.1 are the empirical functions

for sand C-CORE (2008). To accommodate the PIRAM tests, equation 6.1 has been

revised to equation 6.2, C-CORE (2009e).

94

Table 6-5 Sand test results in prototype parameters

Gouge P02 P03 P05 P06 P07 P08 P09

Angle( degrees) 30 30 30 30 30 30 15

Depth(m) 1.3 1.43 0.18 2.3 2.4 0.19 1.2

Width(m) 10 10 2.2 14.4 14.4 2.2 16

Dr 93.6 51.5 •58 50.8 39 68.1 38.6

Fv(MN) 25.3 9.9 0.14 65.2 52.5 0.45 32.4

Fh(MN) 8 7.7 0.095 47 45.4 0.32 28.2

Fv/Fh Ratio 3.15 1.28 1.5 1.39 1.28 1.3 1.15

Speed (mm/s) 0.5 0.5 1.1 1.1 5.5 54.6 56.8

Mound height(m) 3.38 2.145 0.648 3.749 4.032 0.739 3.132

Combined height(m) 4.68 3.575 0.828 6.049 6.432 0.929 4.332

Vertical extent(m) 4.07 3.86 0.53 7.14 7.49 0.54 6.51

Ir 3.1 1.5 2.6 0.97 0.6 2.5 0.94

1.6 • P02 ~ Site 1

G.> P03 Site2 1.4 POS ~ Site 3 on vertical extent

P06 Site4

1.2 • P07 Paulin 1

~ P08 Paulin 2

~ ~ P09 Paulin 3 + T"" 1 P10 Paulin 4 Vl 0 & PR01B-2 Poor 1a

c 0.8

PR01C-1 Poor 1b Q)

~ [•

~ PR01C-2 Poor 2a x Q) PR09-1 A Poor2b (ij

PR09-2 Poor 4a u 0.6 :e G.> PRSA01 Q)

> ~ PRSA02 G.> ~ ;. PRSA03

PRSA04

0.2 G.> PRSAOS

0 -1 0 2 3 4

Dilatancy Index, lr

Figure 6-19 PIRAM model subgouge horizontal displacement profiles C-CORE (2008)

95

5n-----~----~----~----~-----.

4.5

4

i 3.5 E Q)

~ 3 15.. C/1 ~

~ §

i C/1

'iii 1.5

~

Dilatancy Index, lr

• 0 )(

+ * G ~ 'W A ~

I'> 1ll:

• 0

• 0 ~ 0

P02 'W Site 1 P03 A Site 2 P05 • Site 3 P06 'W Site 4 P07 X Paulin 1 POS X Paulin 2 P09 [;> Paulin 3 P10 $ Paulin 4 PR01B-2 "' Poor2a PR01C-1 " Poor2b PR01C-2 0

PR09-1 0 a=300<'

PR09-2 PRSA01 PRSA02 PRSA03 PRSA04 PRSA05

Figure 6-20 PIRAM model subgouge horizontal displacement profiles C-CORE (2008)

Table 6-6 Subgouge relationship parameters

Parameter Symbol Units

Gouge width w M

Gouge depth Ds M

Gouge angle a Deg

Sand relative density RD 0-1

Soil displacement magnitude D M

Soil displacement on ice gouge centerline at ice keel base do M

Horizontal soil displacement on ice gouge centerline at ice keel base dho M

Vertical soil displacement on ice gouge centerline at ice keel base dvo M

Vertical extent of sub gouge defmmations v M . Maximum vertical extent of sub gouge defonnations Ve M

Transverse horizontal distance from ice gouge centreline y M

Atmospheric pressure Pa MPa .

96

Equation: 6.1 C-CORE(2008)

crb(MPa) = 0.09 Ds 1.5

Ir = RD*(10 -ln (crb*1000))- 1

Ve= min [(1 + Vds(Ir-2)) (Ds + Wl3), 5Ds] or 0 iflr >4

Vds = -0.5 for Ir >2 and =0.2 for lr <2

d11o sqrt(crt!pa) lve =2-0.4 Or+ 1) >O

dvo = min[Ds, W 16]

dido= [1- vlvef

Pa = atmospheric pressure, 0.1 MPa

Equation 6.2 C-CORE(2009e)

Q)

> .c

!

crb(MPa) = 0.09 Ds 1'5

lr= RD*(IO -ln (crb* 1000))- 1

ve= min [(1 +0.5lr) (D + Wl5), 1.3 (Ds + Wl5) 5Ds] iflr < 2

min [(2.6+0.65(Ir-4)) (Ds + Wl 5), 5Ds] if2< lr <4 , 0 if Ir > 4

dho sqti(crt/pa) lve = (0.54 I tan a) (1- 0.2 (lr+ l))>O

dvo= min[0.3(D +WI5),Ds, Wl6]

dido= [ 1- vlve]2

Pa = atmospheric pressure, 0.1 MPa

-1.5 u.J.o__...J...._ _ _L,. _ _l __ ..J....._ _ _J

0 0.2 0.4 0.6 0.8 Horizontal DisplacemenUDisplacement at 0

• P02 0 P03

P05

' P06 P07 P08 PR01C-1 PRSA01 Site 3 Site 4

Figure 6-21 PIRAM model subgouge horizontal displacement profiles C-CORE (2009e).

97

Subgouge deformation for 30 degree tests are presented in Figure 6-21 C-CORE (2009e).

The non-zero depth values for displacement of unity indicate those tests where SGD were

not measured directly at the gouge base. These non-zero value profiles should be

considered accordingly in evaluating the quadratic fit.

6.8 Gouge Rate

As shown in Table 6-4, P05 and P08 have the same attack angle of 30 degrees. Both the

gouge depth and gouge width are about the same. The differences for P05 and P08 are the

density (P08 is denser than P05) and the keel speed. Vertical and horizontal forces for

P08 are about three times larger than those in P05. Force ratios for P05 and P08 are all

around 1.45. The combined depth for P08 is higher than P05. The nonnalized subgouge

defom1ation by combined depth for P08 has the same extent but smaller maximum

horizontal subgouge deformation than P05, Figure 6-14. This difference may because of

the sand dilatancy which is 2.5 for P08 and 2.6 for P05. Dilatancy is smaller in P08

because of the higher stain rate. This higher stain rate causes the smaller subgouge

deformation and higher gouge forces from shear induced negative excess pore pressures

ahead of the advancing keel.

Another comparison is between P09 in PIRAM tests and PROIC-2 in PRISE tests,

Table 6-7. P09 was using 30 est viscous pore fluid and PRO 1 C2 was using water

saturated sand. The gouge depth gouge width and soil condition are similar for P09 and

98

PROl C-2. The different gouge rates and pore fluids give nonnalized velocities, V*, of

1,1 00 and 25,500 mm2 /s using a non dimensional fluid viscosity for tests PRO 1 C2 and

P09 respectively. The dimensional relationship of nmmalized velocities was adopted to

[consider ice keel gouge rate in the experiments: V* = v D v. In the above, D and v are

the gouge depth and keel velocity, respectively, and v is the pore fluid viscosity.

Gouge forces for P09 are 2.3 times larger than PR01 C-2. Subgouge deformation for P09

and PROl C-2 is shown in Figure 6-22. P09 has smaller subgouge defonnation than

PR01 C-2 which proves that higher gouge rate resulting smaller subgouge defonnation

and higher gouge forces. The two comparisons indicated that the faster gouge rate may

result in larger gouge forces by a factor of 2 or 3 and smaller subgouge deformation but

similar vertical extent.

subgougc hod zon t o I de forma l ion, lls (I +k)

0 0. 05 0. 1 o. 1s 0.2 1u5 o.:~ 0. 35 0. 4 0

0. 2

! 0.4 'v; 0

" " "" 0. 6

• ~ " ~ 0.8 "' CJ

" 5 "' "0 I

5 ~ .. 1. 2 ;'

1.4

1. 6

Figure 6-22 Subgouge deformation ofthe PIRAM test P09 and PRISE test PROIC-2

99

.----,-------------------------------~--- -----

Table 6-7 Comparison ofthe PIRAM test P09 and PRISE test PROlC-2

Attack Gouge Bearing Max SGD Fh Fv Test Gouge Speed,

angle Ir% Width FviF11 Kappa pressure SGD extent MN MN I. D. Depthm mm/sec

Deg M kpa m m

P09 15 0.94 1.2 16 57 1.15 2.6 195 0.02 0.4 28.2 32.4

PR01C2 15 0.95 1.1 15 10 1.16 2.5 97 0.085 0.25 12.2 14.2

100

7 CONCLUSION AND RECOMMENDATIONS

When the base of an iceberg or pressure ridge ice keel is in contact with the seabed, an

ice keel gouge may be fom1ed . Researchers indicate some of the important factors that

affect ice keel gouge such as soil resistance, ice strength, keel geometry and driving

force. The ice gouge event can pose a significant threat on sub-sea facilities such as

pipelines, cables, wellheads and also templates.

The experiment program is progressed by towing model ice keel across a model testbed

at a set gouge depth in a geotechnical centrifuge. A large amount of data regarding ice

keel gouge in sand was acquired from the experim~nt program and analysis desctibed in

this thesis.

A total of seven tests were conduced in this experiment program. The two first model

tests were conducted relatively slowly in dry, dense, and water-saturated medium density

sand to prove the new equipment and techniques. Two tests are included to compare with

previous Delft Hydraulics flume medium scale gouge tests. Three tests are conducted

with faster gouge rates using a viscous pore fluid to retard excess pore pressure

dissipation.

As the model ice keel is driven in the sand, the soil reaction force increase with the

development of a deep seated beating fai lure mechanism. As the mechanism is

overridden, the load decreases with a corresponding clearing process. These load cycles

have been correlated in all tests to the failure mechanism using PIV.

101

The combined gouge depth has a significant effect on the force and subgouge

deformation. The force per unit width increases as the combined gouge depth becomes

larger. The vertical to lateral gouge force ratio seems independent of aspect ratio or attack

angle. The kappa value which is the frontal bern height nom1alized by gouge depth is

linear with the aspect ratio for deep gouge depth. It seems there is no significant effect

for the kappa value between 15 degree and 30 degree for deep gouge depth. Kappa value

has the significant effect of gouge force and subgouge deformation.

PIV techniques were successfully used to track the evolution of subgouge deformation

for all 7 tests. The maximum horizontal subgouge displacement happens at the base of

the keel and decreases with depth. The associated maximum gouge forces are a function

of the keel attack angle and the gouge geometry.

As compared with previous tests, the vertical extent of subgouge deformation is a

function of combined depth and the soil state, but independent of the attack angle. The

lateral SGD defonnations are influenced by the attack angle and the soil state. The faster

gouge rate may result in larger gouge forces by a factor of 2 or 3 and smaller subgouge

horizontal deformation but similar vertical extent.

As there are only 7 tests presented in this thesis, it has limitations in comparing between

tests to evaluate the effect from some parameters. Such as the soil condition, soil strengtl1

parameters, parametric corTelations and ice keel attack angle. More tests can be taken in

order to validate the conclusions and provide more comparisons. As all the tests are using

102

the same fine sand, other soil condition and soil strength could be considered in future

tests which may effect the attenuation of subgouge deformation and plastic strain of soil.

There are 6 of 7 tests using model ice keel with attack angle of 30 degree. Ice gouging

tests with other attack angles and keel shapes can be conducted to have more

comparisons with 30 degree attack angle keel. Faster gouging rate tests can also be taken

to evaluate the effect of gouge rate on subgouge deformation. The correlations between

parameters should also be considered in future work. As combined depth has the

significant effect on gouge force and sebgouge defonnation, future studies should

examine the extent of the dead wedge within the frontal berm, as well as the magnitude

and rate of SGD attenuation .. Maximum vertical extent of sub gouge deformations should

be examined. Single keel versus multiple fingered keel ice gouging feature on the

subgouge defom1ation should be examined in the future studies.

103

-- ------------ -------~~--------------------------

8 REFERENCES

[1]. . Chari, T.R. (1979) "Geoteclmical Aspects of Iceberg Gouges on Ocean Floors",

Canadian Geotechnical Journal, Vol. 16, No.2: 379-390.

[2]. Chari, T. R. (1975) "Some Geotechnical Aspect of Iceberg Grounding", PhD Thesis

to the Faculty of Engineering and Applied Science, Memorial University of

Newfoundland.

[3]. Clark, J.I. , Paulin, M.J., Poorooshaab, F. (1990). "Pipeline Stability in an Ice-Scoured

Seabed", EUROMS-90, August 20-22, 1990, Trondheim, Norway, pp. 533-549.

[4]. C-CORE (2009a) "PIRAM - Gouge Morphology Study", C-CORE Report R -09-

013-490 v1 , June 2009.

[5]. C-CORE (2009b) "PIRAM - Draft Final Report", C-CORE Report R -09-019-490

v1 , June 2009.

[6]. C-CORE (2008) "PIRAM - Review of Subgouge Defonnation", C-CORE rep011 R-

07-045-491 v2 December 2008.

[7]. C-CORE (1996) "PRISE Phase 3c: Extreme lee Gouge Event - Modeling and

Interpretation", C-CORE Report 96-C32

[8]. Comfort, G., and Graham, B. (1986) "Evaluation of Sea Bottom Ice Gouge Models",

Environmental Studies Revolving Funds Report No. 037, June, 1986.

[9]. Hettiarachir, D.R.P., and Reece, A.R. (1975) "Boundary wedges in two-dimensional

passive soil failure" , Geotechnique 25, 197-220

[1 0]. Kenny, S., Phillips, R., Clark, J., and Nobahar, A. (2005) "PIRSE-Numetical Studies

on Subgouge Deformations and Pipeline/Soil Interaction Analysis".J.I. Clark and

Associates , ST.John's, Canada

104

[11]. King, T., Phillips, R. and Barrett, J . (2008) "Probabilistic Pipeline Burial Analysis for

Protection against lee Scour", ICETECH-08, July 20-23 in Banff, Canada.

[12]. Liferov, P. (2003) "First-year Ice Ridge Gouge and some Aspects of lee Rubble

Behavior", Doctoral Thesis at NTNU 2005:84

[13]. Lanan, G.A. Niedoroda, A.W. , and Week, W.F. (1986) "Ice Gouge Hazard

Analysis",

Proceedings, 18th Annual Offshore Technology Conference, OTC, Volume 4, Houston,

TX, USA, pp.57-66.

[14]. Palmer, A. Konuk, I. , Love, J., Been, K. , and Comfort, G. (1989) "Ice stour

mechanisms . Proceedings", Tenth International Conference on Port and Ocean

Engineering under Arctic Conditions Lulea, 123-132

[15]. Palmer, A.C., Konuk, 1. , Comfort, G. (1990) "Ice Gouging and the Safety of Marine

Pipelines", Paper OTC6371 in Proceedings, Twenty-second Offshore Technology

Conference

[16]. Palmer, A.C., Kenny, J.P., Perera, M.R. and Reece, A.R. (1979) "Design and

operation of an underwater pipeline trenching plough", Geotechnique, 29, 305-322

[ 17]. Paulin, M.J. (1992) "Physical Modeling Analysis of Iceberg Gouge in Dry Sand and

Submerged Sand", M. Eng. Thesis, Memorial University of Newfoundland, St.John's

NF, Canada, 183p

[18]. Poorooshasb, F. (1990). "Analysis of Subgouge Stresses and Probability of Ice

Gouge-Induced Damage for Buried Submarine Pipelines". Contract Report for Fleet

Technology Ltd., C-CORE Contract Number 89-Cl5.

[ 19]. Phillips, R. , Clark, J .I. , and Kenny, S. (2005) "PRISE Studies on Gouge Forces and

Subgouge Deforn1ations", Proc., 18th POAC, 1 Op.

105

[20]. Rinawi, W. (2004)." Particle Image Velocimetry (PIV) applied on ni axial tests",

MSc. thesis, Institut fur Geoteclmik und Tunnelbau, Universitat Innsbruck.

[21]. Surkov, G. A. (1995) "Method for Detem1inirtg the Optimum Burial Profile for

Subsea Pipeline Facilities in Freezing Seas. Disseriation for a Degree of Candidate of

Technical Services", Sakhalin Research and Design Institute.

[22]. Taylor, R.N. (1995) "Geotechnical Centrifuge Technology", Blackie Academic Press.

[23]. Timco, G.W. and Burden, R.P. (1997) "An Analysis of the Shapes of Sea Ice

Ridges", Cold Regions Science and Technology, 25: 65- 77.

[24] . Vershinin, S.A, Truskov, P.A, and Liferov, P.A. (2007) "The action of ice formations

on the underwater objects". In Russian, 196 pages.

[25]. Weeks, W.F., Bamesr, P.W., Rearic, P.M. and Reimnitz, E. (1983) "Statistical

Aspects of Ice Gouging on the Alaskan Shelf of the Beaufort Sea" U.S. Army Cold

Regions Research and Engineering Lab. Repoti 83-21 , 34 pps.

[26]. White, D.J ., Take, W.A. and Bolton, M.D. (2003) "Soil deformation measurement

using particle image velocimetry (PIV) and photogrammetry", Geotechnique 53

7:619-631.

[27] . Woodwotih, C., Nixon, D., and Phillips, R. (1996) "Subgouge Deformations and the

Security of Arctic Marine Pipelines", Offshore Teclmology Conference

106

Appendix A

Table A 1: Site centrifuge sand test program prototype parameters

Relative Attack Gouge Gouge Fh Fv

Test Soil Type Density Angle Depth Width (MN) (MN)

(deg.) (m) (m)

Site 1 Fine Sand 62% 15 1.0 15 13 16.4

Site 2 Fine Sand 73.9% 15 1.9 10 23.6 28

Site 3 Fine Sand 56.2% 30 2.05 10 15 14

Site 4 Fine Sand 71.8% 30 2.75 10 27.8 30.3

' ' ' ' . ' '

2 -l---------- -~------------ -- -~ ---------------l--------------- ~-------------- -i--------------- ~--- ------ ------ ~ -- ------------I ! ! l ! ! l !

:: __ __[" ___ ••• I _ ·-r··-··--: • •• I _ r.• • T _ -t 1 7 ------ -------: -- -----------:--------------:--------------:---------------:---------------:---------------:--------------

~ i i i i i i i ~ · · --------------r---------- ---!-----· -------- -~-------------· ·t-------- -----·i·------------· ·i·--· ---·-----· · l-· -----· ------. · ------··------:--· ·-·--------·r-· ----- -----~---------------:--------------·r·· -----------·r ···· --·······-;· -------------. . -----.------T -----------_l ______ -------r ------------T-- -------;--------------T-------------r------------. · ------·---· · --r-·--· · · --------r· ------------·1----·---------·1·-------------·r·------------·r ------------ ------------

100 300 ...

Figure A. 1 Model Fv/Fh ratio versus ice keel displacement for test P03

107

liD 150 ,., """ ""' '"' Displacement. mm


!I······· Fv/Fh I 19 ··········-··············1···--············-·······-+········· · ····· ··-··· ·····f ········ ···· ··· ···· ···· ·--~- -- -· · · · · ···· ··-···········~ ----················-··· I , , , , ,

! ! ! ! ! i i i i I i

i , r r 1

c ~~~ r:l-1 J : : •••• •••••:••·······~ ~;~~~~:(

I I i v I \

Displacement. mm


108

"L---~~~---.~oo~--~.~oo~--~m~--~~~--~300=---~~=---~~=---~~~--~500~--~~~ Displacement, mm


1 Br-------r-----~r-------r-------,----,--,-------,-------~==~~ Fv/Fh

kL-------,ooL-------,ooL-----~mL-----~~~----~JDOL-----~~~------m~----~~

Oisplacemenl. mm


·I

109

13r----:----~-----:----:-----:-----:----::----:r.= ... = ... ~M~"

. .

·~ 1 ~~ :t~ 1 r 1 r 11

'' J i;,t ~ ' 'i l :~~~r,i + +, + i+ . . .... ~~~'~11. ·:'.! ............ ~, ------- -------! · ~~ . . -· '~--L .......... jJL ......... .

: : : : : : : :


' o I I I I

: :: : I :::::::I _: f : I :L ::_: · ~ : :::: ::::: T ::: : : : T :: ::: ::::::: ::::·:· -:r·:: :: : : : : ___ :_:: __ : __ _ I: -- ---- ---·- -- ----·-·r····- --- r -- --- 1 --- - , --

100 -----------------1------------- ------:------------------: ------------------r------- ---------r-----------------

: -• -·: r: :·::: ::::::.: : ::::: : : r: :: :: ::::r ::::: :.: ~.~------~~~------~.~~------~.~~------~-~-------~-------=-

l lrtMI, f«<

Figure A. 7 Model velocity slope for test P02

110

E E

~~---------;----------;---------~----------T.----~==~

1-velocltyS~pel : I I I • I

350 ------- --------------1----------------------r---------------------r----------------------r------ --------------• I I I

: ----- •• _r-_ • r___ - r r _.- -••• ~

:ii 200 ~-. ~--- ••••••• -------! -------- ---------- ---- ~------------- --- ----- -~- --------------- ---- --~---- -----------------E ! ! ! ! ~ : : : : g. : : : : 0 150 -------------------- -1----------------------~----------------- -----~------------ ------ ----~---------------------cu I I I I

~ j j I I

' ' ---------------------1----------------------j----------------------+------ --------------+---------------------' I I I I 1 I I I I I I I I I I I I I I

50 ---------------------t ----------------------1----------------------1--- ------ -------------r- --------------------• I I I I I I I I I I I I I I I

' ' ' I I I I .. -----------------------~--- ------------------

' ' ' ' ' ' ' '

-so.L------------~~-----------,~~------------,~~------------~~------------~2~ Time, sec


600,---------~----------.----------r----------.----------r---------.

-I'\Jj:-----------;llll;!;;----------;:11±;-ID---------;:,l!D±;-----------:,<I00-±:;----------;:,600±;---------~,IIIl

Time, sec


111

600,------,-------.-------.------.-------.-------.------,.------.-------,

' ' 600 ········--------j·-------·--···--·t------------·--·t··-----------···· ................. --······---------j·----··-- --·---t----·---------·--j---------------

1 m ·····m··· l ·ml=l~"=i m···· ·•mm m••mmm •m•m• ·····, ·············r m••m•m !•••m••m••

r I, 1, ·,1·, 11 r r : : i :

D 1 r r 1 ! 1 r 1 100 -···········-···!···-····-········:···-·········· ··:·········-·······:··········-------:····-·····-------:--····-·······--·:--·-···········--!···············

. . i ! i I i · i

nme,sec

Figure A. I 0 Model velocity slope for test P06

soo,--------,--------~---------,--------,---------~r==7~~ 1- -ySiopol

600 ....................... . . , . . .. . . .. . . ............ . .... : ... . ......... ............. .:. ......................... : .......................... .:. ....................... . : : l : :

: . . i I

c Jr:rr ~ i ~ i 1 !

i I I I I I : : : : !

200 -------------------------r--------------------------~------- -----------------r -------------------------r-------------------------r-----------------------: : : : ;

i i ! i i ~ : l ~ ~

·~~~ -------------------------:------------------ --- -- -- -r--------------------------r-------------------- -- ----i·-------------------------r ·-------------------·--

1 I I I I ~==========~~~====~--~~----------.~~=---------~ .. ~~~~~--------7. .. ~~~--------~.200

nme.se<:


11 2

~,-------~------.--------r-------,-------.-------,-------r __ ~~=.=.~.~~~

«ll ··················t···············-···l·-------------······r·····--·····-······t··--··------------·t··---------------·-t·· --·------·-----·t··--------------·

! 1 j ! l l 350 ··················+······· · ······-----1 ----· · ·------ · · · ·· · - ~ - ------······-·····+-----------····----~---· · · · ·· ····· ·····f······-············+····-············

~ .................. L ................ L ................ r···············J ........................ ············r·················t················· : l : : : ! : : • : :

~ 250 . ................. +-··················i····················t······-···········-t················ --~-----······--·-··· ·-~---·············-·· +···· ···· ·-···· ··· I i i i = : = =

~ m ················+··················l····················l···················t······ ··········-r···················f···················t·················

J 150 ·················+·················l····················f·················· ~-· ··· ··········· ···!·· ················ ··f···· · ····· · ·· ······f ···· ····· · ····· · · 100 ••.••• ••.•.•••••.. + ................... j .................... , ........ ·········f ···················l····················l···················f ·················

50 ··················+···················].. ................. ! ···················+···················l .................. ..l ................... l ................ . 1 j i 1 1 ~ ! : : : : :

Q ••••••••••uoooo•• 0 0

••••••••••t ••• ••••••••••••• •••+•••• ••• ••••••••U••~••••••••••••••••••••~ •••••••••u••••••••+••••••oo•••••••••

l ~ 1 l ~


·~r-------------~------------,--------------r-----r====~~ 1-wloc~) Slope I

- . . - ·······································r·······································-,·······················-·············· ...................................... .

350 ·······································r·······································-r······························ ·······r·····································

:JX) . ...................................... t········································j·······································j······································

~ : i ·······································r· ·······································r····-············ ······················r······································

·······································r·············································-····· ·····························,······································

·······································r-·······································;·· .................................... , ..................................... .

: : r I ! :

4~~--------------~1~~~--------------~.~~- --------------~.~~--------------~1~ Tirnt, IK


113

1<,---------.----------.---------.----------.---------,----------'

I I I I

12 ---------------r----------------r----------------T---------------r---------

1 ---------------r----------------r-----------------r---------------:------ _________ j ________________ _

• ,. ----------------:-----------------r---------------r----------------r _____________ T ______________ _ l ,. i >

L.

0 _________ .,. ____ .,. ____ ,.... __ _,_

' ' ' ' ' ' ' ' ' '

Figure A. 14 Model vertical settlement during centrifuge spin up for P02

E E

' '

' 1 I I I I I I

1.: •••••••••••]•• ••••••••••••!•••• •••••••••!••••••••••• .. ••• • • ••• •••··•r••••••••• ••••!•••••••••••••!•••••••••• ·· ·· , ··· · r· r ·· r -0.5L_ ____ --,.L_ ______ ,L-______ _L_ ______ _J_ ______ _L ______ ..__L ______ __l,.-----~

800 1000 1050 1100 1150 1200

n me, Sec


114

oer------.------r------.------r------.------r------.------r-----0

. . . . . . 07 ............. Ff ::._;.:!· ' ;.:!· .. :;:·i;e.::::·;u"";~"" ... "i .. if .............. T .............. T ................ ! ................ T ............. + .......................... ..

. 1 ~ ~ 1 i ' . 06 ................ r ............... T ............... ~ ................ r ............... : ................ T...... .. ... ~ ................. , ............. ..

t :: ············ri••:::•••r r··············r········ ~·· :•••••••••••••1••·············

I :: •••••• f i• : :••! r ••·········•:••••••••••• :••••••••••••I•••••••••••••r••••••••••• i : : : :

01 ................ , ................. r .............. t ............. r ................. , ................. ]" .............. T ............... 1 ............. ..

0 ................ .. ............ T ................ r ................. , ................. r .............. T ................ 1 ............. ..

T1me.sec


. ' . . 1.8 ......................... l ........ J- S•HJer~ l. ............................................. -................................................ .

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~ 1 ~ l 1 ~ O.G ····················-····1········-·················t ··········· -······· ·i····· ······ ············· · · i··· ········ ················~························

.. I : I I T 0.2 --············· ··········;-··················· ·····;··························;··········-···············;-··························r························

1 ~ l ! l


115

.•· S.Ul.,.nt

i 25 ···················t················ .. ··+····················l············· · ·······~-----···············+···················· i·····················l---· ·····

: ; ; : : : : : ! : : ! l j 1 i ! i ! ! ! i i !

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• ! i i I I ! 15 ··············· ···:······ ··············: ··· ··············· ···: ········ ·········· ···:············ ······t····················j·····················:··········

l!> : : ! : ! ! ! ~ l ! l ! l !

l ! : : : 1 , i , . , , 1 ··················--i----·················t·······--···········j················ ---!---·················t·················--·t···················i··········

! ! ! l

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i i ~;. '

• : I : r li I ::.~~~ J i l l ! i : ! : : !i 0.3 ···--····-·------·---·--··-----;·----------------------------···r·-----·---·· -·-·--·--------i·······-························r·····························

I l ! ! ! -..., l : : I

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~.. :iZi II:: i i i i

~-~~--------~m~----------~~----------~~~----------~~~----------d~ Time, sec


116

4 5 --------------r ---: _________ ! ______ ::~~~l·;------------r------------r-------------r-------------r --···-----·---j--·----------·--t··--------...

4 -----------··r··----------·-r··----------·-r·----------·-r··----------.,.-------------T·-------------r·------ ----··r··-----------·--------- ----

35 -----------··r··---------·--:-·-----------·r··---------·r··---------·r··----------T·----------- r··---------··r··--------·-·r··---------~ 3 ··-··---------1·---·-··--·----+-----··------·i·-·--------····t····-··-·-····-t····-·-··-··--·i···- ----------r------------··t··-------------r-----------·-i i l ; 1 i l ; i 2

.6 ··············(············t·············i···············-r···············j········ ·····l··············-r--············-r··············-r············· i 2 ------------··r ··-------··-r··------------·-------------·-·r···---------- !··-----------··r ··-----------l-------------·-r··------------r--·----------

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1 ··············1················r···············;······· ······-;-···············;···············1················;···············1················;······--·····

.. ! : t t[IIJJ ~ l ~ l ~ l ~

Time,Ht


Figure A. 21 Side view of gouge shape for test P03

117

Figure A. 22 Top view of gouge shape_ for test P05


118

Figure A. 24 Side view of gouge shape for test PO?

Figure A. 25 Top view of gouge shape for test PO?

119


Figure A. 27 Top view of gouge shape for test P08

120


Figure A. 29 Top view of gouge shape for test P09

121

~ ., .0 E

' ' I I I I

46 -----------------·r ·---------------r ·---------------- ----------- ---- ·r ··---------------r·--- ------------41

36 A~ /t

B c 31

i 26 ., E :! u. 21

-.- Keel , Polnl C

16 ----------------··t··--------------(- --- ----------:----------------- r------ =:::::: ~::~:: -----------11 -----------------·1· ----------------- r··- --------------1------------ -----r-----------------! ------------------

• I I I

' ' ' 6 ------------------r---------- -- --- r··----------------1------- ---------r- -----------------; ------------------

2265

2260

2255

2250

2245

2240 ., 2235 ~

::>

2230 ~ Cl

2225 ~

2220 :;

2215 g c

2210 J -c

2205 -E, c

2200 <

2195

2190

2185

2180

2175

1 +-~~~~--~~~~~-4--~~~~-+~~~~~~~~~~~+-~~~~~2170

0 100 200 300 400 500 600

X, mm

Figure A. 30 Frame number versus keel displacement for P02

45,-------~------~. ------~------~--------~--~--~------~------~--~

' I I I I I I I I

:: -------------r-------------r-----:~: :::: :r:: :::::::::: r::-:: ~ _ -::: _::::::::: :: r ::::::::::::1::::::::-::::; _ ::::: ~ i' iii i

' ?j t: ::: : ::r::: : ::::t::: :::·-:;:: ::r: : 33

29

:: -- -- -------~::;: ;:i~: ~-:: L: ::::-:::: -:::: __ :::::I:::::::::::: J:::: :::::::::1::::: _ ::::::: J: ::::::::::::: :::::: Keei, PolntB ! ! ! ! 1 !

_,._ Keel, Point A : , : : : : : 17 -------------, -------------:-- - ----- ----:--------------t----------- --~-- ----- ---- -~------ -- -----~-------------{ ------

" - - ' - -- ~ - + ---- --- ----- T---- - - +--- i-- -

· ----- ::::_ :_:::_r ::::::::r: r:·: L ::F: :: : :r :_::: T 1

100 150 200 250 300 350 400 450 500


2130

2120

2110

2100 ! E ::> z " 2090 g>

_§

2080

2070

2080

2050

122

~

~

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: -- ::: - : _:___ :r:: ::_r ::- -16 ------ --------- - - ------ --- __ : -------------r------ ------r·------------1--------------

- -

- A~ /t

B c - -

• I I : I l 13 -----; -------------- --------------r-------------r-------------10

2472

2466

2460

2454 :;;

~ 2448 ~

" "' 2442 § ....

2436 ~ 0 c

2430 ~

2424 ~

2418

2412

2406

1+-~~~~~~~~~~~~~~~~~-+~~~~~~~~~~~~~-+~~~~~2400

0 100 200 300 400 500 600 700 800

X, mm


66~------~--------~------~--------~------~------~~------~---,.---~ 14140

61

56

A~ 51

46

41 /j

---- .!--------------~ ------------ 14135

14130

14125

14120 .. .0 E

14115 ~ .. "' ..

E 36 14110 § " z .. E 31 !! u.

26

21

16

11

6

"' Cl 14105 g

c .. 14100 ~

.s:

"' 14095 ii:

14090

14085

14080

1 +-~~~-+~~~~~~~~-+~~~~~~~~~~~~~~~~~~~~~~4 14075

0 100 200 300 400 500 600 700 800

X,mm


123

Time (Sec)

996.1 1006.1 1016.1 1026.1 1036.1 1046.1 1056.1 1066.1 1076.1

17 c--------r,-------,,--------~!--------r!-------,,~,-,---~,--------.w~------~ 1600

16 --- _________ :,. i--------------r-----------·-t-· -----------1------------- -~ -- ---------i---------:-... .!--r-------------15 -------------+-------------t-------------+------------- ~ ----------- --: ------ -'------ ~-----:~~-- --- ~-------------

-~ ~~ ~ ~~ ~ :i: ~ ~ ~ ~ ~ ~~ ~~~~ ~ j ~ ~~-: ~- -~ ~-: ~ ~t ~ ~~ ~ ~~ ~~~ ~ ~~:t :~ ~ ~~ ~~~ ~~~~ r~~: ~ ~ ~ ~ ~ ~~~ ~~ A~ ' ' ' . , ' '~ I I I 't I / r --------t ------------- : -- -----------r ------~./--- j-------------- r-------------

8 c ________ i __________ -- r. - ----------r---: . .,!-------1--------- ~----r-------------

..8 10 ---------:------ -- ---- ~ --------------~ ... .:: __________ ~--------------~-------------§ : : f' : : z 9 ------------ -~------- ------- ~-------------+- -- -------- ~ -----------. .....:~~- ------------~-------------- ~-------------~ s ------ _____ __ j ____ ------~- __ i ~ _____ ~-----~~ ____________ j ______ __ ..:~~- __ L _____________ j_ ____ _________ l ___ _________ _ LL : : / ' : • : : :

7 -------------1--------------t-------.t-- --r------------- 1 --:,··---------~-------- · · ------------ - Keel , Point C

6 ------------+------------.f---/ -----+------------.-.]:: __________ +------- ----Keel, Point B -----------

14

13

12

11

1500

1400

1300

1200

1100

1000

900

800

700

600

500

5 ---~--------~+-------------~/-- ---------+------~--.,~~-1~------~-----+-------- ·· · ·· · Keel, Point A -----------

' /: ' . ' ' ' '

400

4 ------- ------~-- --------.t-- '--------------:------,'------ j --.-----------: -------------:--------------:-------.-----

3 --------- ----~------_.f_ --- ~ -------------+-~: ~ -------- ~ ------------- -~-------------~--------------~-------------: / : l·' : : : :

2 -------------;--/-- -------r----------~:=-r·------------ 1·-------------r -------------r-------------r·------------

300

200

100

. 1+-~~~~~~~~~~~~+-~~~-+~~~~~~~~+-~~~-+~~~~o 0 100 200 300 400 500 600 700 800

X, mm


Time (Sec)

83.11 84.11 85.1 1 86.11 87.11 88.11 89.11 90.11 91 .11 92.11 93.11 94.11 95.11 .---~----~----~--~----~--~,-----~ry-~----~----~~~.~--~--~2400

' 2300

81 ---------- _____ t ____________ --! ---------------r --------- !----------______ 1 ______ ---------:---------------

-

A~ - -

/j

2200

2100

2000

1900

1800

1700

1600

~ Q) ~

E " z Q) 0> ..

..§

1 :: - . ~ ~ + :- : :r :: ~ : : J :::::::: ::r :::: ::: B c - - 1500 :;;

1400 f

~ 41 ---------------r------------ - ~ - -------------r------- -----r------------r --------------r---------------31 ---------------i------- -- ----1----------------~- -------------i----------------1---Keel , Point C -----------

! ! ! ! - Keei , PolntB

" 1300 z Q)

1200 g> 1100 ..§

1000

900

BOO l ! , l ! -Keel, Point A

" ---- -- - : : -: --r :- -- :r:- -:_ _::r:::::-:: :-::: :_ : ·:_ :::::: ::::: ~

0 100 200 300 400 500 600 700

X, mm


124

..--:--------------------------------------------------------------

Time (Sec)

142.4 142.9 143.4 143.9 144.4 144.9 145.4 145.9 146.4 146.9 147.4 147.9 148.4 148.9 149.4 149.9

..---r--~-~-~~---~-r-r--~-~--~~rT--r---rr-~r--~,2400

: ::: - :r:-:::_:_J -::::::::::r: _] _:_1:::-:::·r: -____ _ ~ A~

! :: ::: __ ------- r· -------------- ;::::::::::::.1::::: :::::::: >::::: -::::::: i•• :_::: ::::r:::::::::::::·-:~ ! ~ :: ---r : :::r:~~~:~~·i __ :::::::: ~ ~

-

/ l ' - ' ' B c ' '

21

1

0 100 200 300 400 500 600

X, mm


600

500

400

300

200

100 700

125

Physical Modeling of Subgouge Deformations in Sand · Physical Modeling of Subgouge Deformations in...

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