Physical Modelling of A-Jacks Units in Wave Flume Stage 2 Report MHL1901 March 2009

PHYSICAL MODELLING OF A-JACKS UNITS IN WAVE FLUME

STAGE 2

Report No. MHL1901

Department of Commerce Manly Hydraulics Laboratory

Document Control

Reviewed Approved for Issue Issue/ Revision Author Name Signed Name Signed Date mhl1901v4 draft 120209

Indra Jayewardene Rob Jacobs RJ

Final Indra Jayewardene E Couriel EC 12/03/09 Report No. MHL1901 Commerce Report No. 09019 MHL File CME6-0149 First published March 2009 © Crown copyright 2009 This work is copyright. Apart from fair dealings for the purposes of private study, research, criticism or review as permitted under the Copyright Act 1968, no part may be reproduced by any process without written permission. Enquiries should be directed to the Publications Officer, Manly Hydraulics Laboratory, 110B King Street, Manly Vale, NSW, 2093.

Manly Hydraulics Laboratory is Quality System Certified to AS/NZS ISO 9001:2000.

Foreword The report was prepared by the Department of Commerce’s Manly Hydraulics Laboratory (MHL) for A-Jacks Marine Pty Ltd and Rocla Pty Ltd. The testing and reporting was carried out by Indra Jayewardene of MHL. Drafting and publishing was done by Megan Jensen. The report presents the details and results of the model testing.

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Summary In December 2008 Manly Hydraulics Laboratory was commissioned by A-Jacks Marine Pty Ltd and Rocla Pty Ltd to undertake testing of a modified (tapered) A-Jacks unit (Figure 1.1). During testing carried out in 2003 (Stage 1) MHL undertook a physical model study to assess the performance characteristics of the A-Jacks armour unit (MHL 2003). This second series of tests was designed to evaluate the influence of a design modification on the performance of the original unit. The Stage 1 testing of the Ajacks unit involved testing a slender unit and a ‘stubby’ unit which resulted in KD values higher than those obtained from testing existing units such as rock, Hanbars, Antifer cubes and Accropodes. The second stage involved testing a unit which was not as slender or as stubby as the original units tested. The initial test program was undertaken to assess the capability of A-Jacks units to replace other units for the repair of large areas, new construction and for patch repairs. Stage 2 of the testing was undertaken to simulate construction of a new construction and the A-Jacks unit was the only unit under test. The A-Jacks units were placed in a single layer for all the test series. Jonswap wave spectra with 8 s wave peak period were used in the testing. In this study, the surf similarity parameter (ξ) varied from 2.6 to 3.85. This indicates that the wave breaking process went from plunging to surging waves. Ahrens (1975) and van der Meer (1988) suggest that rock armour stability is a minimum during this breaker transition phase. The following conclusions can be drawn based on the model testing described in the study. 5.2 TF A-Jacks Unit - Random Placed Unit – Test Series Results

After 2000 waves at 4.2 m wave height, the single layer 2.33 tonne A-Jacks armour resulted in less than 1% damage. The estimated KD value was 29. The armour was placed at approximately 54 units/100 m2 . 5.2 TF A-Jacks Unit - Bundled Random Placed Unit - Test Series Results After 2000 waves at 6.5 m wave height, the single layer 2.33 tonne A-Jacks armour resulted in less than 1% damage. If the bundled A-Jacks unit is considered to be a unit of 9.33 tonnes (4 times the mass of a single unit ) then the KD value is estimated to be 27. The armour was placed at approximately 66 units/100 m2 . 5.2 TF A-Jacks Unit – Relaxed Bundled Placed Unit - Test Series Results After 2000 waves at 5.5 m wave height, the single layer 2.33 tonne A-Jacks armour resulted in less than 1% damage. The relaxed bundled A-Jacks placed unit is evaluated as a single independent unit of 2.33 tonnes, the KD value was estimated to be 65. The armour was placed at approximately 66 units/100 m2.

Some general considerations regarding the A-Jacks unit follow: • Due to the A-Jacks unit being placed in a single layer, early repair strategies have to be

planned in order to prevent damage to the secondary armour and core. • All the tests were carried out at a slope of 1V:1.5H. • In addition to the coefficient of damage, the density of placement, wave climate, type of

breaking wave, type of placement, permeability and hence core material have to be considered when considering the A-Jacks armour unit for design purposes.

• It is recommended that the ability of the A-Jacks unit as an interface be tested in the event that it is utilised with other larger breakwater units due its high KD value.

• It is recommended that the modified A-Jacks unit be further tested under 3D conditions in a wave basin in order to assess the unit’s performance under the joint action of currents and waves.

The following is a comparison of KD values obtained during testing and historic values obtained for other armour units.

Estimates for KD Values for Commonly Utilised Armour Units

Armour Unit KD Source Rock 2-4 CERC (1984) Core-Loc 16 CLI (2002) Accropode 12 CLI (2002) A-Jacks 24-48 MHL (2003) A-Jacks Random Placed 29 MHL (2009) A-Jacks Bundled Random Placed 27 MHL (2009) A-Jacks Relaxed Bundled Placed 65 MHL (2009)

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Contents

1. INTRODUCTION 1 1.1 Background to Project 1 1.2 Scope of Works and Study Objectives 2 1.3 Description of the A-Jacks Unit 2

2. TEST FACILITY 3 2.1 General 3 2.2 Model Wave and Water Level Conditions 3 2.3 Simulation of Wave Groups 3

3. MODEL SCALING AND TEST SCHEDULE 4 3.1 Model Scales 4 3.2 Model Description and Layout 5 3.3 Armour Units 5 3.4 Model Inspection and Test Regime 6 3.5 Test Schedule 6 3.7 Stability Test Methodology and Criteria for Damage 7

4. TEST RESULTS 9 4.1 5.2 TF A-Jacks Unit - Random Placed Unit – Test Series Results 9 4.2 5.2 TF A-Jacks Unit - Bundled Random Placed Unit - Test Series Results 10 4.3 5.2 TF A-Jacks Unit – Relaxed Bundled Placed Unit - Test Series Results 12

5. CONCLUSIONS AND RECOMMENDATIONS 14

6. REFERENCES 16 APPENDICES

A Wave Measurement Example Time Series Tests B Model Cross-section Details C Model Secondary Armour Distribution

Tables 1.1 Estimates for KD Values for Commonly Utilised Armour Units 2 3.1 Densities, Nominal Weight and Nominal Diameter for Model A-Jacks Units 5 3.2 Details of Model Rock Armour 6 3.3 Test Schedule 6 4.1 A-Jacks Testing - Random Placed A-Jacks Armour Units 9 4.2 A-Jacks Testing - Bundled Random Placed A-Jacks Armour Units 10 4.3 A-Jacks Testing - Relaxed Bundled Placed A-Jacks Armour Units 12 4.4 Estimates for KD A-Jacks Armour Placement During Tests 13 A1 Wave Statistics 18 C1 Distribution Statistics Model (Rock) Secondary Armour Units 21

Figures 1.1 Schematic of the A-Jacks Tapered Unit 1.2 The A-Jacks Bundled Unit 2.1 Flume Layout 4.1 Random Placed Unit Cumulative Damage History 4.2 Random Placed Unit Cumulative Damage History 4.3 Random Placed Unit Cumulative Damage History 4.4 Random Placed Bundled Unit Cumulative Damage History 4.5 Bundled Unit Cumulative Damage History 4.6 Bundled Unit Cumulative Damage History 4.7 Relaxed Bundled Unit Cumulative Damage History 4.7 Relaxed Bundled Unit Cumulative Damage History A1 Example of Probe Time Series A2 Example of Probe Time Series B1 Test Cross-section B2 Estimation of the Nominal Diameter of an A-Jacks Unit C1 Model Secondary Armour Distribution

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Symbols and Abbreviations D50 = Equivalent diameter of M50 rock armour Hsig = Significant wave height of time series L = Wave length TP = Peak period of spectrum W50 = Mass of 50% percentile in rock armour distribution ν = Kinematic viscosity Re = Reynolds number Δ = Relative mass density (ρa - ρw )/ ρw ρa = Mass density of armour ρw = Mass density of fluid in which armour is immersed ξ = surf similarity parameter

1. Introduction 1.1 Background to Project Manly Hydraulics Laboratory (MHL) undertook a physical model study in 2003 to assess the performance characteristics of the A-Jacks armour unit (MHL 2003 - Stage 1 Testing). In December 2008 MHL was commissioned by A-Jacks Marine Pty Ltd and Rocla Pty Ltd to undertake a second stage of testing of a 5.2 TF A-Jacks unit (Figure 1.1). This second series of tests was designed to evaluate the influence of design modifications on the performance of the unit. Many formulae are used to assess the hydraulic performance of breakwater units. One of the more accepted formulae is the Hudson equation (CERC 1984). In this series of tests (Stage 2) the Hudson equation was utilised (as in previous testing) to compare the performance of the A-Jacks breakwater unit with other units such as rock armour, Hanbars and Core-loc. When comparing units the nature of the ‘placement’ of the unit must be considered, as placement in a prototype situation could add costs to a construction project and be constrained by the specific site. For the 5.2 TF A-Jacks unit three types of placement were tested. They were: • Random Placed – as opposed to pattern placed • Bundled – as pictured in Figure 1.2 four units are placed together. The dimensions of the

unit enhance this capability. When the axes of these bundles are not in the same direction the placement was classified as bundled and random placed. In the prototype construction the units would be bundled together utilising stainless steel ties. In the model rubber bands were utilised

• Relaxed Bundled – in order to simulate the loosening of ties around the bundles, the rubber bands around the placed bundles were cut. This is to simulate conditions when the ties came loose.

The previous A-Jacks unit tests (MHL 2003) resulted in a KD values in the range of 24-48 when the toe was fixed using bundled A-Jacks units. Only irregular waves were used for these tests. The KD values obtained at the O.H. Hinsdale Laboratory at Oregon State University (OSU) varied from 24 to 292 (Amortech 1999). Both regular waves and irregular waves were used for the tests carried out by OSU. Selection of a single KD for general design purposes is not recommended. Important parameters to define a range of appropriate values for design include packing density, wave steepness, breaking versus non-breaking waves, including type of breaking wave, armour slope and core material. Table 1.1 tabulates KD values quoted in the literature.

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Table 1.1 Estimates for KD Values for Commonly Utilised Armour Units

Armour Unit KD Source Rock 2-4 Foster (1973), SPM (1984), MHL (1996) Core-Loc 16 CLI (2002) Accropode 12 CLI (2002) A-Jacks 24-48 MHL (2003)

The test programme was developed in consultation with Mr Frank Atkinson, the inventor of the unit. Mr Atkinson of A-Jacks Marine and Mr Michael Carnell, Product Manager of Rocla Pty Ltd, were present for the testing. 1.2 Scope of Works and Study Objectives The brief for the physical model study specified the following testing: • the A-Jacks unit’s performance with random placement on trunk and bundled placement

at toe • the A-Jacks units with the units bundled and placed randomly on trunk with bundled

placement at toe • the units with the bundles initially placed in a regular manner and then the bundles cut

free (relaxed bundled). 1.3 Description of the A-Jacks Unit All values specified in the report are in prototype units unless mention is made of model units. Figure 1.1 indicates a schematic of the A-Jacks unit. The unit is dimensionally characterised by two ratios, specifically the waist ratio and the fillet ratio:

r = T/C

s = F/T where

r = waist ratio T = arm thickness C = end to end length of unit s = fillet ratio F = fillet length along the axis of an arm

The size to weight ratio varies with design (waist ratio and fillet ratio, etc.) and the concrete density. The waist ratio for the modified A-Jacks unit is 1/5.2. The fillet ratio is 1/2. Stage 1 tests (MHL 2003) were carried out for waist ratios of 1/6.3 and 1/4.1 and fillet ratios of 11/13 and 2/5.2.

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2. Test Facility 2.1 General The physical model testing was carried out in MHL’s random wave facility (Figure 2.1). The flume is 30 m long, 1.8 m deep and 1 m wide. In the MHL flume, regular and random waves are generated by a sliding wedge wave paddle driven by a servo-hydraulic system. A dissipative beach was constructed at the opposite end of the flume. The floor of the flume was constructed in 1.2 m plywood segments to replicate the bathymetry slopes utilised in Stage 1 of the testing. The design cross-section was built in the 10 m glass section of the flume for model inspection, photography and video filming. 2.2 Model Wave and Water Level Conditions Random waves were generated according to a Jonswap-type energy spectrum. During this model study the spectrum was defined by the wave height and periods described in Section 3. The selected design wave conditions resulted in both plunging and surging breakers on the breakwater model. All model tests were undertaken for a duration of 2,000 waves. A water level of 0.0 m AHD was utilised for all the tests to represent mean sea level. For this testing 2000 waves represents a storm duration of 5 hours, which is representative of a recorded extreme storm. The testing cycle was broken into 1000 and 2000 wave cycles so as to observe any incremental damage for each wave height tested. A sample of measured wave statistics for Jonswap spectra is provided in Appendix A. 2.3 Simulation of Wave Groups

The importance of examining the wave groups of a wave regime has long been recognised when testing structures in the ocean. The Department of Public Works and Services (DPWS), as part of its coastal program, initiated a study to investigate and compute the groupiness of wave conditions measured along the NSW coast (Jayewardene et al. 1993). In the flume the groupiness factor was used to measure the grouping effect of waves measured in deeper water. As a part of this investigation, only a qualitative study was carried out on the effect of grouping on the structure. A time series that resulted in high grouping effects was used for all the tests.

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3. Model Scaling and Test Schedule 3.1 Model Scales A length scale of 30 was selected for the test program. The length scale was selected on the basis of the dimensions of the structure to be modelled, armour sizes, water levels, wave heights and the need to minimise scale effects. The time scale was determined from the length scale using Froudian similitude (Hughes 1993). The mass scale takes into account the differences in density between sea water in the prototype and fresh water used in the model. In order to satisfy the stability number criterion (Hughes 1993) Mr = (Hp/ Hm)3(ρp / ρm)(Δm / Δp)3 the ratio (ρp / ρm) is the ratio of prototype armour density to model armour density. Δ is the relative density (ρa / ρw - 1). ρa is the density of the A-Jacks armour and ρw is the density of water. Length scale L r = 30 Time scale Tr = √Lr = 5.58 Mass scale Mr = Lr

3 ρr / Δr3 = 30,820

Several investigators have provided indicators of the limiting size of models for reduced Reynolds number effects or scale effects (Dai and Kamel 1969). More recently Cornett (1995) determined the condition for negligible scale effect as: Hsig > (ν Re / D50) 2 / g = 0.081 m where Hsig = Significant wave height ν = Kinematic viscosity = 1.14 x 10-6 m2 /s Re = Reynolds number = 2.5 x 104 D50 = Nominal diameter of A-Jacks primary armour (Appendix A) = 0.48L D50 = Nominal diameter of A-Jacks bundled armour = 0.76L L = Length of A-Jacks armour unit The smallest armour unit used on the breakwater head was the 2.33-tonne Taper Fit A-Jacks armour that had an equivalent model diameter of 3.2 cm. All tests were undertaken with a model Hsig greater than 10 cm. The water depth in the vicinity of a coastal structure has a significant influence on the amount of offshore wave energy reaching the structure. It also influences wave runup, drawdown and overtopping forces acting on the structure. It is not only the elevated high water levels during a storm that can affect a coastal structure. During times of low water, damage to the toe of the breakwater can also occur during a storm event.

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The water depths to be used in the estimation of breakwater armour size are dependent on the still water level (SWL), the mean water level including any wave setup, and the bed levels surrounding the structure. During the first stage of testing it was evident that waves were plunging on the cross-section toe as well as overtopping the structure, therefore to replicate these conditions the same cross-section dimensions (Appendix B) and the same water level were maintained (0.0 m AHD) throughout the testing. 3.2 Model Description and Layout The study was undertaken in the MHL random wave flume. The operator defines the peak frequency and wave height of a Jonswap spectrum to be generated. The computer controls the data acquisition from the wave recording probes. The transfer function of the flume was obtained prior to constructing the test section in order to obtain estimates of incident wave height. The incident wave height was obtained by utilising the transfer function of the wave generator prior to constructing the test cross-section in the flume. The bottom slope utilised for Stage 2 was identical to that used in Stage 1of the testing in order to compare test results. An 8 m depth was simulated at the breakwater section in the flume. The depth fell away sharply due to a 1:5 slope a short distance from the toe. The constructed breakwater cross-sections for all the tests are indicated in Appendix B. All the tests were carried out at a test structure slope of 1V:1.5H. Extensive testing carried out by van der Meer (1988) indicates that the permeability of the core has an influence on the stability of the breakwater. Within limits discussed by van der Meer, the more permeable the breakwater core, the higher the stability. Since this investigation compares the performance of differing placements of the same armour unit it was necessary to ensure that the core and the toe conditions remained similar during all model testing. 6 mm diameter blue metal was used for the core. The distribution for secondary armour used in the testing was stipulated by the client and is included in Appendix C. The secondary armour was approximately 10% by weight of the primary armour. 3.3 Armour Units

For the A-Jacks unit the nominal diameter was considered to be Dn where; ρDn3 = W50 and ρ

is the density of the unit and W50 the nominal weight. Table 3.1 indicates the values for density and nominal diameter for the model A-Jacks units utilised in the modelling. The equivalent prototype weight and equivalent diameter are 2.33 tonnes and 0.96 m respectively.

Table 3.1 Densities, Nominal Weight and Nominal Diameter for Model A-Jacks Units

Type of Unit Specific

Gravity Nominal Weight

W50 (gms) Nominal Diameter

Dn (cm) A-Jacks Unit 2.3 75.6 3.2 Bundled A-Jacks Unit 2.3 302.4 5.1

Details of the rock armour used in the model testing are described in Table 3.2. Grading curves for the secondary rock armour are included in Appendix C. The equivalent prototype weight is 0.26 tonnes.

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Table 3.2 Details of Model Rock Armour

Armour Unit Nominal Secondary

Armour Weight W50 (gms)

Specific Gravity

Linear Scale

Details of Model Armour Weight and

Grading Curve Rock (Secondary Armour - Small) 8.6 2.66 30 W85 / W15 of 2.42 *

*see Appendix C for grading curves of model rock armour

3.4 Model Inspection and Test Regime Representatives of A-Jacks and Rocla were present throughout the testing and assisted MHL in all facets of the testing. The model arrangement and layout were confirmed and the testing set-up and procedure were approved by both representatives. 3.5 Test Schedule Table 3.3 presents the schedule of tests that were conducted. All values are expressed in prototype units.

Table 3.3 Test Schedule

Test No. Repair Strategy Armour

Wave Height (m) *

Comments

1(a)–1(d)

2.33 tonne single layer random placed A-Jacks at a density of 52 units/ 100 m2. A specially constructed toe with bundled units was used

3.0 3.5 4.2 4.8

After bedding in the test cross-section at a wave height of 2 m, a wave height of 3.0 m was used for the start of the tests

2(a)–2(e)

2.33 tonne single layer random bundled A-Jacks at a density of 66 units/100 m2 to test interface

4.2 4.8 5.5 6.0 6.5 6.7

After bedding in the test cross-section at a wave height of 2 m, a wave height of 4.2 m was used for the start of the tests

3(a)–3(d) 2.33 tonne single layer relaxed bundled but placed A-Jacks at a placement density of 66 units/100 m2 using a stone and Stubby interface

3.5 4.2 4.8 5.5 6.0

After bedding in the test cross-section at a wave height of 2 m, a wave height of 3.5 m was used for the start of the tests

*water level was maintained at 0.0 m AHD and the peak period of the Jonswap spectrum was maintained at 8.0 s

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3.7 Stability Test Methodology and Criteria for Damage

3.7.1 Bedding-in Tests

A bedding-in test of 500 waves using a wave height of 2 m was completed prior to testing the cross-sections under more extreme wave conditions. This procedure was undertaken to ensure that conditions similar to the development of storm wave conditions were simulated and the newly constructed structure was not subject to extreme wave attack without adequate settlement of the armour units. 3.7.2 Damage Measurement Two damage definitions are used in breakwater modelling. One uses the erosion area (S) and requires the use of a cross-section profiler. The other definition, used in this investigation, relates damage to the movement of a primary armour unit. If the unit moved more than the distance of one nominal diameter (Dn) it is considered to be damaged. For the A-Jacks unit the nominal diameter was considered to be Dn (Appendix A) where ρ Dn

3 = W50, and ρ is the density of the unit and W50 the nominal weight. Table 3.1 indicates the values for weights and nominal diameters obtained for the model units as supplied by A-Jacks Marine Pty Ltd. Percentage damage is defined to be the percentage of displaced armour. The total number of units is taken to be the total number of units subject to wave action. For this investigation the total number of units on the cross-section were counted. It should be noted that for milder wave conditions where runup and rundown do not affect the total length of cross-section, conservative estimates of damage may result when the total number of units on the cross-section are counted. During testing in Stage 1, it was noted that some armour units, particularly at the toe of the structure, were observed to have rocking motions. This rocking motion, although not contributing to an increase in damage of the structure, would increase the impact loadings on the adjacent individual units. Structural testing of the individual units was beyond the scope of this study. Damage due to this rocking is unknown. Tests carried out by van der Meer (1988) indicate damage to a section built with rock armour is dependent on the duration of the storm. No data exists to establish if the stability of A-Jacks units is dependent on storm duration, hence in this investigation each test run was carried out for a total of 2000 waves or an equivalent of a four- to five-hour storm. After each series of 1000 waves the damage was noted and the test section was videoed and photographed. The test waves were generated from a selected time series to ensure high grouping effects on the structure. Hudson’s equation was used to obtain the relationship between dimensionless wave height or stability number (Hsig / ΔDn ) and KD as follows: Hsig / ΔDn = (KD Cot α)1/3 where Hsig = significant wave height Δ = relative mass density KD = coefficient of damage Dn = nominal diameter of M50 armour (Appendix A) α = angle of breakwater slope

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Also

ξ = surf similarity parameter

O

sig

LH

αtan=

where a value of less than 2.5 indicates plunging breakers, a value greater than 4 indicates surging breakers and intermediate values indicate a mixture of plunging and surging breakers α = structure slope Hsig = significant wave height at toe of structure Lo = wave length in deep water The value of KD at a given level of damage to a structure was used to compare the efficiency of the A-Jacks unit with armour units such as quarry rock, Accropodes and Core-loc. In addition to the coefficient of damage, the density of placement, structure slope, wave climate, type of breaking wave, type of placement and core material have to be considered when comparing the A-Jacks armour unit with other units for design purposes.

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4. Test Results 4.1 5.2 TF A-Jacks Unit - Random Placed Unit – Test Series Results The details of each individual test run undertaken for the A-Jacks physical model study are provided in Table 4.1. Figures 4.1 to 4.8 present a selection of photographs taken during the model tests. Appendix B indicates the cross-section utilised in the testing.

Table 4.1 A-Jacks Testing - Random Placed A-Jacks Armour Units

Test No. Type of Armour

Wave Height

(m) Comments*

1 2.33 tonne single layer A-Jacks at a density of 54 units/100 m2. 318 units were used in the construction. The toe was constructed utilising bundled units. The crest was reinforced with larger units

3.0

After 2000 waves at 3.0 m no damage was recorded (Figure 3.1)

2 2.33 tonne single layer A-Jacks at a density of 54 units/100 m2. The toe was constructed utilising bundled units. The crest was reinforced with larger units 3.5

After 1000 waves no units were displaced. After 2000 waves at 3.5 m no units were displaced, however the units had become compacted and secondary armour was visible. 8 units were added to fill the gap (Figure 4.2b)

3 2.33 tonne single layer A-Jacks at a density of 54 units/100 m2. This included 8 additional units. The toe was constructed utilising bundled units

4.2

After 1000 waves at 4.2 m, 2 units were displaced (Figure 4.3a). After 2000 waves at 4.8 m 6 units were displaced .

4 2.33 tonne single layer A-Jacks at a density of 54 units/100 m2. This included 8 additional units. The toe was constructed utilising bundled units 4.8

After 1000 waves at 4.8 m, 13 units were displaced (Figure 4.4a). After 2000 waves at 4.8 m 18 units were displaced. The cross-section was considered to be sufficiently damaged to stop further testing

*water level was maintained at 0.0 m AHD and the peak period of the Jonswap spectrum was maintained at 8.0 s

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In this series of tests, the surf similarity parameter (ξ) varied from 3.25 to 3.85. This indicates that the wave breaking process went from plunging to surging waves. Ahrens (1975) and van der Meer (1988) suggest that rock armour stability is at a minimum during this breaker transition phase The results of the testing program outlined in Table 4.1 can be summarised as follows: • An initial test was carried out on the A-Jacks unit after bedding in the units using 500

waves at 2 m wave height. After 2000 waves at 3.0 m and 3.5 m wave heights no damage was visible.

• After 2000 waves at 3.5 m wave height, the single layer 2.33 tonne A-Jacks armour resulted in less than 1% damage. The estimated KD value was 17.

• After 2000 waves at 4.2 m wave height, the single layer 2.33 tonne A-Jacks armour resulted in less than 1% damage. The estimated KD value was 29. The armour was placed at approximately 54 units/100 m2 .

• After 1000 waves at 4.8 m wave height 6 units were displaced and after 2000 waves 13 units were displaced. The damage increased rapidly and at 2100 waves 18 units were displaced. At this point in the testing it was deemed that the cross-section was damaged.

Details of the armour damage and aspects of the testing are provided in Figures 4.1 to 4.4(b) and Appendix B. 4.2 5.2 TF A-Jacks Unit - Bundled Random Placed Unit - Test Series Results The bundled unit simulates four A-Jacks units tied using stainless steel wire in prototype. In the model the units were bundled utilising rubber bands. The total weight of the four units was 302.4 gms. The bundling of the units enabled placement at a higher density than the 52 units per 100 m2 achieved when placement was random and single. The bundling resulted in a placement density of 66 units per 100 m2. Details of each individual test run undertaken as part of this type of placement of the A-Jacks unit tests are provided in Table 4.2.

Table 4.2 A-Jacks Testing - Bundled Random Placed A-Jacks Armour Units

Test No. Type of Armour

Wave Height

(m) Comments*

1 2.33 tonne bundled A-Jacks at a density of 66 units/100 m2. The toe was constructed utilising bundled units. The crest was reinforced with larger units

4.2

After 2000 waves at 4.2 m no damage was recorded (Figure 3.1)

2 2.33-tonne bundled A-Jacks at a density of 66 units/100 m2. The toe was constructed utilising bundled units. The crest was reinforced with larger units

4.8

After 2000 waves at 4.8 m no damage was recorded however the units had become compacted and secondary armour was visible (Figure 4.4(b))

3 2.33 tonne bundled A-Jacks at a density of 66 units/100 m2 .This included 8 additional units. The toe was constructed utilising bundled units

5.5

After 2000 waves at 5.5 m, damage was recorded on the crest but no damage was recorded on the trunk (Figure 4.5)

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Test No. Type of Armour

Wave Height

(m) Comments*

4 2.33 tonne single layer A-Jacks at a density of 66 units/100 m2. The toe was constructed utilising bundled units 6.0

After 500 waves the toe was reinforced and testing was continued to 2000 waves. No damage was observed on the trunk

5 2.33 tonne single layer A-Jacks at a density of 66 units/100 m2. The toe was constructed utilising bundled units 6.5

After 500 waves the toe was reinforced and testing was continued to 2000 waves. No significant damage was observed on the trunk

6 2.33 tonne single layer A-Jacks at a density of 66 units/100 m2. The toe was constructed utilising bundled units 6.7

After 500 waves at 6.7 m, the toe was badly damaged and the secondary armour layer was visible at several locations (Figure 4.6)

*water level was maintained at 0.0 m AHD and the peak period of the Jonswap spectrum was maintained at 8.0 s

In this study, the surf similarity parameter (ξ) varied from 2.6 to 3.25. This indicates that the wave breaking process was transitioning a mixture from surging to plunging waves. The results of the testing program outlined in Table 4.2 can be summarised as follows: • An initial test was carried out on the A-Jacks units using 500 waves at 2 m wave height.

Subsequently 2000 waves, at each of the wave heights from 4.2 m to 6.5 m, resulted in minor or no significant visible damage.

• After 500 waves at 6.7 m wave height, the single layer 2.33 tonne A-Jacks armour resulted in damage to the trunk resulting in exposure of the secondary armour and visible damage to the toe.

• If the bundled A-Jacks unit is considered to be a unit of 9.33 tonnes (4 times the single unit and an equivalent diameter of 1.52 m) then the KD value is estimated to be 27. The armour was placed at approximately 66 units/100 m2 .

Details of the armour damage and aspects of the bundled armour are provided in Figures 4.4(b)-4.6.

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4.3 5.2 TF A-Jacks Unit – Relaxed Bundled Placed Unit - Test Series Results The details of each individual test run undertaken as part of Stage 2 of the A-Jacks unit tests are provided in Table 4.3.

Table 4.3 A-Jacks Testing - Relaxed Bundled Placed A-Jacks Armour Units

Test No. Type of Armour

Wave Height

(m) Comments*

1 2.33 tonne single layer A-Jacks at a density of 66 units/100 m2. The toe was constructed utilising bundled units. The crest was reinforced with larger units

3.5

After 2000 waves at 3.5 m no damage was recorded (Figure 4.7(b))

2 2.33 tonne single layer A-Jacks at a density of 66 units/100 m2. The toe was constructed utilising bundled units

4.2 After 2000 waves at 4.2 m, no damage was recorded (Figure 4.8(a))

3 2.33 tonne single layer A-Jacks at a density of 66 units/100 m2. The toe was constructed utilising bundled units

4.8 After 2000 waves at 4.8 m, 2 units were displaced (Figure 4.8(b))

4 2.33 tonne single layer A-Jacks at a density of 66 units/100 m2. The toe was constructed utilising bundled units

5.5 After 2000 waves at 5.5 m, 4 units were displaced (Figure 4.8(c ))

5 2.33 tonne single layer A-Jacks at a density of 66 units/100 m2. The toe was constructed utilising bundled units 6.0

After 2000 waves at 5.5 m, 8 units were displaced and the structure was considered to be damaged.

*water level was maintained at 0.0 m AHD and the peak period of the Jonswap spectrum was maintained at 8.0 s In this study, the surf similarity parameter (ξ) varied from 2.85 to 3.55. This indicates that the wave breaking process went from plunging to surging waves. The results of the testing program outlined in Table 4.3 can be summarised as follows: • An initial test was carried out on the A-Jacks units using 500 waves at 2 m wave height.

Subsequently 2000 waves, at each of the wave heights from 3.5 m to 5.5 m, resulted in minor or no significant visible damage, with two units being displaced.

• After 2000 waves at 6.0 m wave height, the single layer 2.33 tonne A-Jacks armour resulted in damage to the trunk.

• The relaxed bundled A-Jacks placed unit is evaluated as a single independent unit of 2.33 tonnes, the KD value was estimated to be 66. The armour was placed at approximately 66 units/100 m2.

Estimates for KD values obtained during the testing are given in Table 4.4.

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Table 4.4 Estimates for KD A-Jacks Armour Placement During Tests

A-Jacks Armour Unit Placement

Estimates of A-Jacks KD for Different Armour

Placements During Tests

Placement Density (units/100 m2)

Random 29 54 Bundled Random Placed 27 66 Relaxed Bundled Placed 65 66

5. Conclusions and Recommendations The Stage 1 testing of the A-Jacks unit (MHL 2003) involved testing a slender unit and a stubby unit which resulted in KD values higher than those obtained from testing other units such as rock, Hanbars, Antifer cubes and Accropodes. The second stage involved testing a unit which was not as slender or as stubby as the original units tested. The initial test program was undertaken to assess the capability of A-Jacks units to replace other units for the repair of large areas, new construction and for patch repairs. Stage 2 of the testing was undertaken to simulate construction of a new structure and the A-Jacks unit was the only unit under test. The A-Jacks units were placed in a single layer. In this study, the surf similarity parameter (ξ) varied from 2.6 to 3.85. This indicates that the wave breaking process went from plunging to surging waves. Ahrens (1975) and van der Meer (1988) suggest that rock armour stability is a minimum during this breaker transition phase. The following conclusions can be drawn based on the model testing described in the study. 5.2 TF A-Jacks Unit - Random Placed Unit – Test Series Results After 2000 waves at 4.2 m wave height, the single layer 2.33 tonne A-Jacks armour resulted in less than 1% damage. The estimated KD value was 29. The armour was placed at approximately 54 units/100 m2 .

5.2 TF A-Jacks Unit - Bundled Random Placed Unit - Test Series Results

After 2000 waves at 6.5 m wave height, the single layer 2.33 tonne A-Jacks armour resulted in less than 1% damage. If the bundled A-Jacks unit is considered to be a unit of 9.33 tonnes (4 times the single unit ) then the KD value is estimated to be 27. The armour was placed at approximately 66 units/100 m2 .

5.2 TF A-Jacks Unit – Relaxed Bundled Placed Unit - Test Series Results

After 2000 waves at 5.5 m wave height, the single layer 2.33 tonne A-Jacks armour resulted in less than 1% damage. The relaxed bundled A-Jacks placed unit is evaluated as a single independent unit of 2.33 tonnes, the KD value was estimated to be 65. The armour was placed at approximately 66 units/100 m2.

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Some general considerations regarding the A-Jacks unit follow: • Due to the A-Jacks unit being placed in a single layer, early repair strategies have to be

planned in order to prevent damage to the secondary armour and core. • In addition to the coefficient of damage, the density of placement, wave climate, type of

breaking wave, type of placement, permeability and hence core material have to be considered when considering the A-Jacks armour unit for design purposes.

• It is recommended that the ability of the modified A-Jacks unit as an interface be tested in the event that it is utilised with other larger breakwater units due to its high KD value.

• It is recommended that the 5.2 TF A-Jacks unit be further tested under 3D conditions in a wave basin in order to assess the unit’s performance under the joint action of currents and waves.

The following is a summary of KD values obtained during testing and comparison with historic values obtained for other armour units.

Estimates for KD Values for Commonly Utilised Armour Units

Armour Unit KD Source Rock 2-4 CERC (1984) Core-Loc 16 CLI (2002) Accropode 12 CLI (2002) A-Jacks 24-48 MHL (2003) A-Jacks Random Placed 29 MHL (2009) A-Jacks Bundled Random Placed 27 MHL (2009) A-Jacks Relaxed Bundled Placed 65 MHL (2009)

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6. References Ahrens, J.P. 1975, Large Wave Tank Tests on Rip Rap Stability, Coastal Engineering

Research Centre, Technical Memorandum No. 51, US Army Corps of Engineers.

Amortec, 1999, A-Jacks Concrete Armour Units, Technical Report Moffatt & Nichol Engineers .

Coastal Engineering Research Centre, 1984, Shore Protection Manual, Department of the Army, USA, 4th Edition, 1984.

Core-Loc International 2002, Historical Overview of Armour Units.

Cornett, A. 1995, A Study of Forcing and Damage of Rock Armour on Rubble Mound Breakwaters, PhD Thesis, Technical Report HYD-TR-005, National Research Council, Canada.

Dai, Y. B. and Kamel, A. M. 1969, Scale Effect Tests for Rubble Mound Breakwaters, Waterways Experiment Station, Research Report H-69-2, Department of the Army, USA.

Manly Hydraulics Laboratory 1996, Laboratory Measurement of Oblique Irregular Waves on a Rubble Mound Breakwater, MHL Report No. 782 (draft).

Manly Hydraulics Laboratory 2003, Physical Modelling of A-Jacks Units in Wave Flume – Stage 1, MHL Report No. 1251.

Foster, D. and Gordon, A. D. 1973, Stability of Armour Units Against Breaking Waves, 1st Australian Conference on Coastal and Ocean Engineering, Institution of Engineers Australia.

Hughes S A, 1993, Physical Models and Laboratory Techniques in Coastal Engineering, Advanced Series on Ocean Engineering, Volume 7, World Scientific-pp 183.

Jayewardene, I. F. W., Haradasa, D. K. C. and Tainsh, J. 1993, Analysis of Wave Groupiness, 11th Australasian Conference on Coastal and Ocean Engineering, Institution of Engineers, Australia, Townsville, August 1993.

van der Meer, J.W 1988, Deterministic and Probabilistic Design of Breakwater Armour Layers, Journal of Waterway Port and Coastal Engineering, January 1988.

Appendix A

Wave Measurement Example Time Series Tests

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Appendix A Wave Measurement

Random Wave Facility and Model Construction In the MHL random wave flume waves are generated by a sliding wedge wave paddle driven by a servo-hydraulic system. The flume transfer function is used during the tests to differentiate between the incoming wave and the reflected wave. The floor of the flume is adjustable in 1.2 m segments. The floor was adjusted at the start of the project to best approximate the slopes utilised in stage 1 of the testing. The design cross-section was built in the 10 m glass section of the flume for model inspection, photography and video filming. The toe of the cross-section was at a level of 0.0 m CD. The waves were generated at a level of -17.0 m CD. The floor slope gradually increased from being flat at the point of generation to a slope of approximately 1:7 at the structure. Wave Conditions Random waves were generated according to a specified Jonswap energy spectrum defined by the wave height and peak spectral wave period. All model tests for stability were undertaken up to a total durations up to 2000 waves. Wave Statistics Wave statistics are provided in Table A1.

Table A1 Wave Statistics

Time Series (m ) Hmax/Hs Hs (m)

Jonswap Spectrum1 Tp (s)

Wave Peak Period1 1 1.62 3.5 8.02 2 1.76 4.2 8.02 3 1.63 4.8 8.29 4 1.60 5.5 7.91 5 1.58 6.5 8.14 6 1.49 6.7 8.50

1 gamma = 3.3

Wave Probes The wave probes were calibrated at the start and end of testing. The probe closest to the structure (P1) was placed 4.5 m away from the structure. The distance from probe P1 to P2 was 3.30 m, from P2 to P3 was 0.8 m and from P3 to P4 was 0.6 m (Figure 2.1). Sample wave forms for probe P1 to P4 are provided in Figures A1 and A2. These wave heights were recorded when a Jonswap spectrum was generated (for time series 1 and 2).

Appendix B

Model Cross-Section Details

Appendix C

Model Secondary Armour Distribution

Pluto 3D Model Weight Distribution for Secondary Armour

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

4 6 8 10 12 14 16 18

Weight(g)

Pass

ing

(%)

Figure C1 Model Secondary Armour Distribution

Table C1 Distribution Statistics Model (Rock) Secondary Armour Units

Mass W15 (gms)

Mass W50 (gms)

Mass W85 (gms)

6.3 8.6 15.0

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