ROCK MASS CHARACTERIZATION - SRMEG
Transcript of ROCK MASS CHARACTERIZATION - SRMEG
1
ROCK MASS CHARACTERIZATION
Wulf Schubert
2Short Course Singapore 11 Klima, Schubert
Rock mass properties
INTRODUCTION
■ Characterization is the process to attach physical paramters to the geological model
■ Parameters are required for modelling of ground- and system behaviour
■ In rock usually discontinuities control the behaviour, thus simplification by „smearing“ discontinuities into a continuum can lead to completely wrong results
■ Sometimes a good sketch and simple kinematical considerations are better than a sophisticated (but wrong) model
2
3Short Course Singapore 11 Klima, Schubert
Rock mass properties
EXAMPLE OF EFFECT OF SIMPLIFICATION
Direct modelling of joints „ubiquitous“ joints Joints smeared into continuum
4Short Course Singapore 11 Klima, Schubert
Rock mass properties
HOW TO ARRIVE AT GROUND PROPERTIES
■ When attempting to characterize ground, followingquestions should be considered already in the beginning:
□ What will I do with the parameters? □ Is it for a feasibility study or a detail design?□ Which modes of failure can be anticipated?□ Which models will I use for analysis?□ Which parameters will I need for construction?□ How much simplification is admissible in order not to loose
essential information
3
ROCK AND ROCK MASS PROPERTIESFAILURE MECHANISMS
6Short Course Singapore 11 Klima, Schubert
Rock mass properties
CHARACTERIZATION
■ For an appropriate design, considering the groundcharacteristics, as well as project specific requirements and boundary conditions, a sound mechanical model is required
■ To be able to create a model, one has to determinephysical properties of the ground, assess influencingfactors, and determine potential failure modes
■ This requires some knowledge about basics of rock mechanics
4
7Short Course Singapore 11 Klima, Schubert
Rock mass properties
FAILURE MODES INTACT ROCK
■ Tensile failure
□ Pure tensile failure very rare, as pure tension seldom exists□ Tensile strength≈UCS/(10-20)
fracturesource
Plumouse failure structures
8Short Course Singapore 11 Klima, Schubert
Rock mass properties
BRITTLE FAILURE
■ Brittle failure
□ Common failure for brittle rocks with low confining pressure□ In brittle rocks under low
confining stress microcracksdevelop in direction of themaximum applied load
□ Microcracks develop dueto tensile stress perpendicularto load direction
□ Tensile stresses caused byinternal heterogeneity
□ With increasing load the cracks grow□ Eventually small columns
buckle
5
9Short Course Singapore 11 Klima, Schubert
Rock mass properties
INTERNAL HETEROGENEITY
■ Rock is composed of variousconstituents with different properties, leading to non uniform stress field and localtension
10Short Course Singapore 11 Klima, Schubert
Rock mass properties
BRITTLE FAILURE
■ If rock is foliated and loaded +/- parallel to foliation, crackwill develop on foliation planes
6
11Short Course Singapore 11 Klima, Schubert
Rock mass properties
SIMULATION OF BRITTLE FAILURE
RFPA
12Short Course Singapore 11 Klima, Schubert
Rock mass properties
SHEAR FAILURE
■ Shear failure
□ Failure mode for brittle rocksunder higher confining stress
□ Confining stress requiredfor brittle rocks
□ Microcracks parallel tomain stress direction are formed
□ Inclined connection betweenmicrocracks with continuing strain
□ Eventually failurealong shear plane
7
13Short Course Singapore 11 Klima, Schubert
Rock mass properties
Failure localization with acoustic emmission sensors
Figure: GFZ Potsdam
Distributed crackingin initial phase
Concentration of cracksprior to shear failure
14Short Course Singapore 11 Klima, Schubert
Rock mass properties
INFLUENCE OF FABRIC
8
15Short Course Singapore 11 Klima, Schubert
Rock mass properties
SHEAR FAILURE, STRESS-STRAIN CHARACTERISTIC
Developmentof microcracks
Connection of microcracksDevelopmentof shear plane (zone)
Sliding alongshear plane
16Short Course Singapore 11 Klima, Schubert
Rock mass properties
SIMULATION OF SHEAR FAILURE
RFPA
9
17Short Course Singapore 11 Klima, Schubert
Rock mass properties
DEVELOPMENT OF SHEAR ZONE BY LATERAL DISPLACEMENT
18Short Course Singapore 11 Klima, Schubert
Rock mass properties
RIEDEL SHEARS
10
19Short Course Singapore 11 Klima, Schubert
Rock mass properties
QUASI DUCTILE FAILURE
■ Materials with low brittleness or brittle materials under high confining stress show „ductile“ failure
■ No or low strength drop after peak
20Short Course Singapore 11 Klima, Schubert
Rock mass properties
FAILURE ENVELOPE
11
21Short Course Singapore 11 Klima, Schubert
Rock mass properties
COMMON FAILURE CRITERIA
smccc
331
sin1
cos2
sin1
sin131
c
tannc Mohr-Coulomb
Hoek-Brown
22Short Course Singapore 11 Klima, Schubert
Rock mass properties
COMMENTS ON FAILURE CRITERIA
■ Due to changing failure mechanisms depending on thestress conditions, a linear failure criterion is very unlikelyfor rocks
■ A huge number of empirical failure criteria can be found in literature for different rock types
■ Post failure behaviour usually not considered
12
23Short Course Singapore 11 Klima, Schubert
Rock mass properties
Peak and residual strength
Cai et al 2007
24Short Course Singapore 11 Klima, Schubert
Rock mass properties
INFLUENCES ON FAILURE & DEFORMATION CHARACTERISTICS
■ Rock structure (foliation, mineralogical composition, etc.)
■ Shape and size of samples
■ Water contents
■ Temperature
13
25Short Course Singapore 11 Klima, Schubert
Rock mass properties
INFLUENCE OF LOADING ORIENTATION
26Short Course Singapore 11 Klima, Schubert
Rock mass properties
INFLUENCE OF LOADING ORIENTATION
Shearing along foliation
14
27Short Course Singapore 11 Klima, Schubert
Rock mass properties
DISCONTINUITIES
■ In general discontinuities have no or very low tensilestrength and no cohesion
■ Shear strength depends on:
□ Rock type□ Roughness□ Rock strength□ Filling□ Loading conditions
28Short Course Singapore 11 Klima, Schubert
Rock mass properties
15
29Short Course Singapore 11 Klima, Schubert
Rock mass properties
BASIC FRICTION ANGLE
■ Basic friction angle fb of joints is determined on a planarsurface
■ Shear strength of planar discontinuity:
max = n*tan fb
n ….. normal stress
30Short Course Singapore 11 Klima, Schubert
Rock mass properties
ROUGHNESS
■ Roughness of joints increases initial shear strength
□ Under low normal stress the sample displaces also perpendicular to the shearing direction (dilation)
in tanmax
n
res
i
16
31Short Course Singapore 11 Klima, Schubert
Rock mass properties
ROUGHNESS
■ Under high normal stress asperities are sheared off
n
res
Schubbruch im Gestein
t+i
cG
G
res
Aufgleiten Abscheren
ns n
Sliding on asperitiesshearing of asperities
shearing of intact rock
32Short Course Singapore 11 Klima, Schubert
Rock mass properties
Influence of normal stiffness
■ If a block cannot dilateunrestricted, the normal stress increases duringshearing, increasing also thepeak shear strength
N= const
kn
17
33Short Course Singapore 11 Klima, Schubert
Rock mass properties
BARTON´S SHEAR STRENGTH CRITERION
■ Consideration of joint roughness, rock strength and block size
r
n
n
JCSJRC
logtanmax
JRC Joint Roughness CoefficientJCS Joint Compressive Strength
002,0
0
0
JRC
n
LL
JRCJRC
003,0
0
0
JRC
n
L
LJCSJCS
34Short Course Singapore 11 Klima, Schubert
Rock mass properties
NORMALIZED JOINT ROUGHNESS–SHEAR DISPLACEMENT RELATIONSHIP
Barton, Bandis, Bakhtar
18
35Short Course Singapore 11 Klima, Schubert
Rock mass properties
JRC PROFILES BY BARTON & CHOUBEY
Barton & Choubey
36Short Course Singapore 11 Klima, Schubert
Rock mass properties
DIFFICULTY TO ESTIMATE JRC
■ As the JRC is determined visually, there is the potential of a strong bias. Different people arrive at different values
Result of 21 persons estimating JRC on the same sample (Schieg 2006)
19
37Short Course Singapore 11 Klima, Schubert
Rock mass properties
GRASSELLIS SHEAR STRENGTH CRITERION
A0 area of the joint surface which is orientatedtoward the shear direction
Ac potential contact area
C „roughness“ parameter - describes theconcavity of the fit function
Θ*max maximum apparent dip angle
φr residual friction angle
σc Uniaxial compressive strength
Decreasing cumulative distribution of thepotential contact area Ac related to surface areaversus the apparent dip angle
18
DA Schieg
38Short Course Singapore 11 Klima, Schubert
Rock mass properties
SURFACE CHARCTERIZATION BY STEREOPHOTOGRAPIC METHODS
Surface elements facing the shear direction arehighlighted depending on the inclination
DA Schieg
20
39Short Course Singapore 11 Klima, Schubert
Rock mass properties
COMPARISON OF SHEAR STRENGTHS
Schieg, 2006
METHODS FOR THE DETERMINATION OF ROCK MASS PARAMETERS
21
41Short Course Singapore 11 Klima, Schubert
Rock mass properties
PURPOSE & METHODS
■ For the analysis of engineering projects (stresses, deformation, etc.) we need material parameters
■ With the current state of the analysis tools and material laws, a direct modelling of all features of rocks and rock masses is not possible
■ Thus a „homogenization“ or „upscaling“ is required
■ Direct modelling, starting from the microscale,stepwise develop material models and upscale
■ Simplified analytical models
■ Empirical or semi-empirical methods
42Short Course Singapore 11 Klima, Schubert
Rock mass properties
MULTILAYER MODEL
a5
b1
a2
a3
a4
a1
b2
b2b3
b4
l1
l2
BA
ial
1
1
ibl
1
1
Material A: EA, AMaterial B: EB, B
Volumetric proportions:
22
43Short Course Singapore 11 Klima, Schubert
Rock mass properties
DEFORMATION MODULUS FOR MULTILAYER MODEL
BA
BA
EEEl
bE
aE
l
l
BA
iB
iA
11
1
BA EE
E
1
Condition: no shear bond between layers A and B
AB
44Short Course Singapore 11 Klima, Schubert
Rock mass properties
DEFORMATION MODULUS FOR MULTILAYER MODEL
Shear bond between layers A and B
Simplified:
BsA EE
EE
,
2
1
BB
BBBs
EE
121
1,
.EA .EB and transv,B transv,A
Es,B ... Stiffness modulus material B
23
45Short Course Singapore 11 Klima, Schubert
Rock mass properties
MULTILAYER, deformation parallel to layers
B A
BAII EEE
0
500
1000
1500
2000
2500
0 20 40 60 80 100
proportion of material A (%)
E-m
od
ulu
s (M
Pa)
E parallel
E normal
EA=2.000 MPaEB=200 MPa
Example for influence of loading direction on stiffness
46Short Course Singapore 11 Klima, Schubert
Rock mass properties
JOINTED ROCK MASS
■ Representing joint properties with a normal stiffness:
knsEi
EiEm
*1
Amadei & Goodman, 1981
Ei ….E-modulus intact rock (MPa)Em …..E-modulus rock mass (MPa)s………spacing (m)Kn ….. joint normal stiffness (MPa/m)
Amadei & Goodman
0
100
200
300
400
500
600
700
800
900
0 0,5 1 1,5 2 2,5
s
Em
Example for Ei =1000 MPa, kn=3000 MPa/m
24
47Short Course Singapore 11 Klima, Schubert
Rock mass properties
CONSIDERATION OF JOINT CLOSING
0
50
100
150
200
250
300
0 0,1 0,2 0,3 0,4 0,5
Normal displacement
No
rma
l str
es
s
Measured
System
Joint
System + Joint
Pötsch, 2007
48Short Course Singapore 11 Klima, Schubert
Rock mass properties
CLASSIFICATION
■ Classification is the procedure to group rock massesaccording to some attributes or quality. Selection of parameters and weighting is purely empirical
■ Example:
□ fracture frequency: 3-4 per m rating: 16□ UCS: 50-70 MPa rating: 7□ joint spacing: 0,5 m rating: 12□ joint condition: slightly rough rating: 20□ ground water: none rating: 15
total rating: 70
Class: good rock
25
49Short Course Singapore 11 Klima, Schubert
Rock mass properties
CHARACTERIZATION
■ Characterization of rock masses involves the description and quantifiaction of properties. Information can be directly usedfor modelling
■ Example
□ Rock type: limestone, not karstified□ Bedding thickness: 20-40 cm□ UCS: 50 – 70 MPa□ Deformation modulus: 15-20 GPa□ Number of joint sets: 2□ Joint spacing: set 1: 40-60 cm; set 2: 50-70cm□ Relative orientation between joint sets: perpendicular□ Roughness: rough□ Basic friction angle: 30° -32°□ etc.
50Short Course Singapore 11 Klima, Schubert
Rock mass properties
CLASSIFICATION
■ Basic idea of classification systems was, to allow assessingrock mass quality and „design“ excavation and support also by people with poor engineering background, usingstandardized parameters and „look-up tables“ for theweighting of the parameters
■ Rating systems used for classification are based on specificexperience, thus the use in other conditions may lead to a misjudgment
■ Parameters used are always the same, some may beirrelevant for certain ground conditions
■ Different combinations of parameters can produce thesame rating
■ By reduction of a number of properties to a single numberinformation is lost
26
RMR – ROCK MASS RATING
rock strength (0 - 15)
RQD (0 - 20)
joint spacing (0 - 20)
joint condidtion (0 - 30)
ground water (0 - 15)
joint orientation (0 – (-12))
RMR
Rock Mass Rating
(0 - 100)
52Short Course Singapore 11 Klima, Schubert
Rock mass properties
DISCUSSION ON RMR
■ RQD is a measure for the fracturing of a rock mass. In addition joint spacing is considered, which basically shouldshow in the RQD.
■ RQD is a measure for the core recovery and should indicatethe degree of fracturing. Measured is the length of the corepieces longer than 100 mm.
■ Orientation of boreholes in relation to discontinuityorientation can lead to a strong sampling bias
■ Joint orientation and ground water may vary locally. RMR forthe same rock mass can be different in different locations
27
53Short Course Singapore 11 Klima, Schubert
Rock mass properties
54Short Course Singapore 11 Klima, Schubert
Rock mass properties
28
Q – ROCK MASS QUALITY
RQD (0 - 100)
Number of joint sets (0,5 - 20)
Jr joint roughness (0,5 - 4)
Ja - joint condition (0,75 - 20)
Jw – ground water (0,05 - 1)
SRF – stress red. factor (0,5 - 400)
(0,001 - 1000)
SRF
Jwx
Ja
Jrx
Jn
RQDQ
56Short Course Singapore 11 Klima, Schubert
Rock mass properties
PARAMTERS FOR Q
29
57Short Course Singapore 11 Klima, Schubert
Rock mass properties
PARAMTERS FOR Q
58Short Course Singapore 11 Klima, Schubert
Rock mass properties
PARAMTERS FOR Q
30
59Short Course Singapore 11 Klima, Schubert
Rock mass properties
PARAMTERS FOR Q
60Short Course Singapore 11 Klima, Schubert
Rock mass properties
PARAMTERS FOR Q
31
61Short Course Singapore 11 Klima, Schubert
Rock mass properties
PARAMTERS FOR Q
Update 1994
62Short Course Singapore 11 Klima, Schubert
Rock mass properties
DISCUSSION ON SRF
■ SRF contains ratings for weakness zones intersecting thetunnel, for rock stress problems like low stress levels close to the surface or rock burst, as well as squeezing and swelling
■ This means, one should know the behaviour to be able to assess rock mass quality.
□ In all engineering problems, it is understood that behaviour canonly be assessed after the material characteristics and theinfluencing factors have been determined
32
63Short Course Singapore 11 Klima, Schubert
Rock mass properties
EXAMPLE FOR INCONSISTENCY OF SRF
Palmstroem & Broch, 2007
64Short Course Singapore 11 Klima, Schubert
Rock mass properties
(MIS)USE OF RATING SYSTEMS
■ Rock mass parameters are derived from rating
□ First various information is collected, then condensed to a singlenumber. From that single number again a number of independent parameters is derived (UCSm, Em,…)
■ Recommendations on support are given withoutconsideration of project specific requirements and groundbehaviour
■ Some even attempt to correlate deformations, advancerates, permeability, etc. with ratings
34
67Short Course Singapore 11 Klima, Schubert
Rock mass properties
SUMMARY RATING SYSTEMS
■ Such systems may be applied in very early stages of a project when information is very limited, to get an overall„feeling“ of support requirements
■ They cannot reasonably be used to design excavation and support, as different failure mechanisms, time dependentbehaviour, deformations, and project specific boundaryconditions cannot be considered
■ Unfortunately rating systems are widely (mis)used due to theapparent simplicity of application
68Short Course Singapore 11 Klima, Schubert
Rock mass properties
Correllation ?
35
69Short Course Singapore 11 Klima, Schubert
Rock mass properties
Correllation ?
Sapigni et al, 2002. Int. J.RM&MSCi
70Short Course Singapore 11 Klima, Schubert
Rock mass properties
CONCLUSION CLASSIFICATION
■ Schematic classification systems on the first glance appearattractive, as they are easy to use – no specific knowledgerequired
■ But: rock masses are very complex, and can exhibit a number of different behaviours
■ The behaviour and project specific boundary conditions and requirements need to be considered to arrive at a reasonabledesign
■ Applying prefabricated systems, which were developed forspecific conditions in most cases will lead to a non-optimaldesign
36
SOME EMPIRICAL MODELS
72Short Course Singapore 11 Klima, Schubert
Rock mass properties
E-MODULUS BASED ON RMR
100*2 RMREM
10 40
10
RMR
ME
BieniawskiBieniawski
SerafimSerafim & Pereira& Pereira
Em (GPa) Bieniawski ; Serafim&Pereira
0,00
20,00
40,00
60,00
80,00
100,00
120,00
140,00
160,00
180,00
200,00
0 20 40 60 80 100 120
RMR
Em
(G
Pa)
Bieniawski
Serafim & Peirera
37
73Short Course Singapore 11 Klima, Schubert
Rock mass properties
E-MODULUS BASED ON EI AND RMR
100cos15,0
RMREiEm
Mitri et al 1994 Em/Ei nach Mitri
0,00
0,20
0,40
0,60
0,80
1,00
1,20
0 20 40 60 80 100 120
RMR
Em
/Ei
74Short Course Singapore 11 Klima, Schubert
Rock mass properties
RMi – Rock Mass Index
■ Palmstrøm combines the UCS of the intact rock with a jointing parameter to arrive at the index RMi, which represents the rock mass strength ( ) JPRMi ccm *
38
75Short Course Singapore 11 Klima, Schubert
Rock mass properties
DETERMINATION OF JP
jAjRjLjC /*
76Short Course Singapore 11 Klima, Schubert
Rock mass properties
GEOLOGICAL STRENGTH INDEX (GSI)
■ The Geological Strength Index has similarities with the classification systems discussed above, however it is not a rock mass classification system
■ It is a simple index value used to quantify the influence of the discontinuities on the ground strength (Hoek-Brown failure criterion)
■ It combines only two parameters, namely the block volume (representing the overall degree of fracturing of the rock mass) and joint state (representing the frictional characteristics of the discontinuities) into one value
39
77Short Course Singapore 11 Klima, Schubert
Rock mass properties
GSI
E-MODULUS BASED ON GSI AND Q
QEM log25
cM QE 3
1
10
Hoek et al.Hoek et al.20022002
ffüür Q > 1r Q > 1
100
cc QQ
BartonBarton
ffüür Q < 1r Q < 1
40
10
101002
1
GSIcDEm
40
10
102
1
GSIDEm
sc<100MPa sc>100MPa
Hoek & DiederichsHoek & Diederichs20062006
)1
2/102.0(
)11/)1560(( GSIDim e
DEE
40
79Short Course Singapore 11 Klima, Schubert
Rock mass properties
EVALUATION OF GSI
■ Besides estimating the GSI from the chart, Chai et al proposed an evaluation as follows:
with Vb block volume (cm3)Jc joint condition (-)Ja joint alterationJs small scale roughnessJw waviness
bC
bCCb VJ
VJJVGSI
ln0253,0ln0151,01
ln9,0ln79,85,26,
A
SWC J
JJJ
80Short Course Singapore 11 Klima, Schubert
Rock mass properties
EVALUATION OF GSI
Qualitative description Waviness rating Jw
Stepped 2,75 Undulating 1,75
Planar 1,00
Qualitative description Waviness rating Js
Rough 2,50 Smooth 1,50
Slickenslided 0,75
Joint contact Filling / Alteration Description Ja
Healed joints Impermeable filling (quartz, epidote, etc) 0,75
Fresh rock walls No coating of filling of the joint surface, except for (possible) staining
1,00
Slightly weathered joint The joint surface exhibits one class higher weathering then the rock
2,00
Highly weathered joint The joint surface exhibits two classes higher weathering then the rock
4,00
Sand, silt, calcite filling etc. Coating of friction surfaces without clay 3,00Roc
k w
all c
onta
ct
(„cl
osed
fea
ture
s“
acco
rdin
g to
IS
RM
)
Clay, chlorite, talg etc. Coating of friction surfaces with cohesive, “lubricating” minerals
4,00
Sand, silt, calcite filling etc. Filling with frictional material without clay
4,00
Compacted clay materials “Hard” filling with softening and cohesive materials
6,00
Soft clay materials Low over-consollidation of the filling material, loose filling with clay
8,00
Fil
led
join
ts w
ith
part
ial o
r no
con
tact
be
twee
n ro
ck w
all
surf
aces
(“g
appe
d an
d op
en f
eatu
res”
ac
cord
ing
to I
SR
M)
Swelling clay minerals Filling material exhibits swelling properties
10,00
41
Rock mass strength - empirical
a
cbc sm
3
31
28
100exp
GSI
m
m
i
b
9100
expGSI
s
5,0a
Für GSI > 25
Für GSI < 25 0s
20065,0
GSIa
Hoek et al.
82Short Course Singapore 11 Klima, Schubert
Rock mass properties
MOHR COULOMB PARAMETERS FROM GSI
■ Radoncic used closed for solutions for a parametric study, and proposes reduction factors for c and :
Reduction factor for cohesion fc Reduction factor for friction f
Radoncic 2008
42
83Short Course Singapore 11 Klima, Schubert
Rock mass properties
ANISOTROPIC ROCK MASSES
■ Foliated rocks have a strong anistropic behaviour. Homogenization thus should be done with care. Strengthand deformation properties have to be assigned fordifferent directions.
■ In particular shear strength may be very low parallel to thefoliation.
■ Strength usually is higher perpendicular to the foliation
■ When simplification is done, care has to be taken not to loose characteristic behaviour
■ When tunnel axis is +/- parallel to foliation, influence of foliation shall be always considered
84Short Course Singapore 11 Klima, Schubert
Rock mass properties
FAULTED ROCK MASSES
■ Fault zones very rarely are homogeneous, but can have a wide variety of compositions
■ We should distinguish between:
□ Fine grained cohesive□ Sandy, non cohesive□ Corse, non cohesive□ Block in matrix
■ Faults in general anisotropic, with low shear strength in direction of main movement, in particular when fault gougedeveloped during shearing
43
85Short Course Singapore 11 Klima, Schubert
Rock mass properties
CHARACTERISTICS OF FAULT ZONES
■ Fault and shear zones may have blocksmillimeters to 100s of meters large
■ Block size distributions in general scaleindependent
■ Block ratio important for strength and deformability
5 cm, 5 m, 5 km
Medley, 2006
86Short Course Singapore 11 Klima, Schubert
Rock mass properties
TYPICAL BRITTLE FAULT ZONE
44
87Short Course Singapore 11 Klima, Schubert
Rock mass properties
Blocks in the North Anatolian Fault Zone
88Short Course Singapore 11 Klima, Schubert
Rock mass properties
DIFFERENT APPEARANCES OF A FAULT ZONE
45
89Short Course Singapore 11 Klima, Schubert
Rock mass properties
BLOCK IN MATRIX
90Short Course Singapore 11 Klima, Schubert
Rock mass properties
46
91Short Course Singapore 11 Klima, Schubert
Rock mass properties
CHARACTERIZATION OF BIM ROCKS
■ Important is the Block-Matrix ratio, as it has an influenceon the strength
-5
0
5
10
15
20
25
30
0 20 40 60 80 100
Volumetric Block Proportion (%)
Incr.. F
riction
An
gle, d
egrees
Scott Dam melange
Physical modelsIrfan and Tang, 1993
conservative trend (Lindquist 1994a)
Scott Dam melange
© Dr. E. Medley http://bimrocks.geoengineer.org
92Short Course Singapore 11 Klima, Schubert
Rock mass properties
CHARACTERIZATION OF BIM ROCKS
■ A significant increase of stiffness can be expected with a block content above 25%. Example of possible influence:
E‐Modulus vs Block/Matrix ratio
0
500
1000
1500
2000
2500
0 10 20 30 40 50 60 70 80 90 100
Percentage blocks
E‐Modulus
E block 2.000 Mpa
E matrix 200 MPa
47
93Short Course Singapore 11 Klima, Schubert
Rock mass properties
STRENGTH OF TECTONIZED ROCKS
■ Habimana (2002) proposes a modified Hoek Brown criterium in relation to the degree of tectonization
asm *)*( 331
Sandstones
Phyllitic shists
94Short Course Singapore 11 Klima, Schubert
Rock mass properties
STRESS DEPENDENT DEFORMABILITY
n
papakEi
3*
Habimana, 2002Example of stress dependent E Modulus according to Habimana
0
100
200
300
400
500
600
700
0 5 10 15 20 25 30
Sigma3 (MPa)
E-M
od
ulu
s (M
Pa)