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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
1
Short Course Singapore 2011
Rock
Klima, Schubert
Rock
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
The Rock Cycle
drawing: USCShttp://3dparks.wr.usgs.gov/nyc/images/fig6.jpg
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Graph: USCShttp://3dparks.wr.usgs.gov/nyc/images/fig6.jpg
The Rock Cycle
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
GraniteIgneous (magamatic) rock, plutonic rock
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
BasaltIgneous (magamatic) rock, vulcanic rock
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Sediments(“soil”) over consolidated silt / clay
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Sandstonesedimentary rock
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Limestonesedimentary rock
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Metamorphic RocksMineral Assemblage Change: Shale to Schist
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Slate very low grade metamorphic rock
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Phyllitelow grade metamorphic rock
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Dolomite – marblemedium grade metamorphic rock / carbonatic rock
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Mica Shistmedium grade metamorphic rock
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Gneishigh grade metamorphic rock
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
How to name rocks
• Mineral constituents
• Chemical composition (magmatic rocks)
• Texture / structure / microtexture
• Grain size (sedimentary rocks)
• Geological position (magmatic rocks: plutonite– vulcanite)
• Genesis of rocks Recommendations by the IUGS Subcommissions on the
Systematics of Igneous Rocks and Metamorphic Rocks
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
How to name rocks
• main constituent: constituent (mineral) present in modal content ≥50%.
• major mineral constituents: constituent (mineral) present in modal content ≥5%.
• minor constituents: constituent (mineral) present in modal content <5%.
• essential constituent: constituent (mineral) that must be present in a rock in a certain minimum amount to satisfy the definition of a rock
• critical constituent: constituent (mineral) indicating by its presence or absence distinctive conditions for the formation of a rock and/or a distinctive chemical composition of a rock.
• Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks: Web version 01/02/07
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Composition
Fabric
Origin
XRD analysis, optical microscopic scanning, chemical analysis
Optical macro – microscopical inspection, XR texture analysis, microspicalautomated interactive image analysis
Fabric elements, mineral paragenesis, geological considerations
A proper rock name is derived from:
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Microscope
Thin Section
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Short Course Singapore 2011
Rock
Klima, Schubert
X-RAY Diffractometer
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Principle of X-Ray Diffraction
Bragg's LawThe layers of a crystal act like weak reflecting mirrors for the X-
rays. Only if the path difference of the reflected X-rays is a whole number of wavelengths does constructive interference occur. This is described by Bragg's Law:
nλ = 2dsinθ
λ: wavelength of the X-raysd : the spacing of the layersθ: the incident angle of the photons
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Principle of X-Ray Diffraction
XRD Pattern of a mixture of Minerals
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Properties appointed by:
• mineral composition
• texture / structure / microtexture
• history of origin / genesis
• condition / weathering / alteration
ROCK (Intact rock)
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Klima, Schubert
Example: Serpentinite
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Rock Fabric:Texture and Structure
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Short Course Singapore 2011
Rock
Klima, Schubert
Fabric:The complete spatial and geometrical configuration
of all components (penetrative fabric elements, scale dependent) that make up a rock
Texture:Geometrical aspects of the
component particles of a rock, including size, shape and
arrangement;
Also:
Degree of crystallographic lattice-(or shape-) preferred orientation of
components
Structure:The presence of compositional
layering, folds, foliation, fractures, lineation . .
(scale dependent!)
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Rock
Klima, Schubert
Rock (Micro-) Fabric:Elements, Terms Symmetry
different types of voids (microcracks, pores), their size, orientation and distribution
disturbance of crystallites (free space in the solid matrix)
voids
vector data (shape preferred orientation); scalar data (grain shape, grain size)
geometry (morphology) of crystallites (related to the solid matrix)
microstructure
crystallographic preferred orientation (e.g., quartz c-axes etc.)
preferred orientation of lattice of crystallites (related to the solid matrix)
texture
ExampleAspect of materialElements of rock fabric
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Rock Section displayingcomposition and microfabric elements of thematerial
(Shape, Size, Interlocking, arrangement of grains)
Original Photograph
Line Drawing
ExplodedDiagram
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Klima, Schubert
Scope O: outlines of porphyroclasts and ribbons
Scope I: elongate parent grains, transgranular and grain-boundary microcracks
Scope II: recrystallised grain mosaique, subgrain boundaries and complete microcrack pattern
Example „scopes“ of fabrics:
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Some Microstructural Indices
Perimeter LP is the length of all edge pixels outlining an object
Shape Factor SF is an expression of the circularity of an object. SF is calculated as:
A = area of grain
LP = perimeter of grain
SFA
LP
=4
2
π
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Some Microstructural Indices
Compactness is a numeric expression of the shape of an object as it moves from a circle to a line. Compactness is calculated as:
A = area of grain
LP = perimeter of grain
CompactnessLAP=
2
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Klima, Schubert
Some Microstructural Indices
Aspect ratio AR is a numeric expression of grain elipticity. AR is calculated as:
Dmax = major axis length
Dmin = minor axis length
ARDD
= max
min
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Klima, Schubert
Some Microstructural Indices
Index of grain size homogeneity : t (index of “textural”homogeneity introduced by Dreyer 1973. t is calculated as:
Aavg = average grain area
Ai = area of individual grain
[ ]t
A
A A
avg
i avg
=−∑ ( )2
12
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Klima, Schubert
Some Microstructural Indices
Feret’s diameter: Feret's diameter is the greatest distance possible between any two points along
the boundary of a region of interest. Dequiv is calculated as:
A = grain area
DA
equiv =⎛⎝⎜
⎞⎠⎟
412
πminimumFeret‘s diameter
maximumFeret‘s diameter
ΘL, ΘB = angle
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Some Microstructural Indices
Index of interlocking: g (Dreyer1973) calculates the complexity of grain-grain relationships. g is calculated as:
n : number of grain considered
Ai : area of exposed grain section
LPi: portion of the grain perimeter which contacts neighboring grains
gn
=⎛
⎝⎜⎜
⎞
⎠⎟⎟∑1
12
L
AP
i
i
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Some Microstructural Indices
Foliation index: F (Tsidzi 1986) is calculated as:
Mi : content of phase i
Si : shape factor (aspect ratio)
F M Si in i
n
=⎛⎝⎜
⎞⎠⎟
=∑1
100
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Rock
Klima, Schubert
Texture-Coefficient (Howarth & Rowlands 1987)
Considers:Grain ShapeGrain OrientationGrain Interlocking
AW Weighting factor for packing densityN0 Number of grains with aspect ration <2.0N1 Number of grains with aspect ration >2.0FF0 Mean value of the Form Factors of all grains with aspect ratio <2.0; FF describes the deviation of grains from circular shape and the
roughness of the grain boundary respectivelyAR1 Mean value of all aspect ratios >2.0
AF1 Angle factor, a measure of the degree of constant grain orientation and the deviation of the max Feret’s diameter from a reference direction
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Rock
Klima, Schubert
Texture-Coefficient (Howarth & Rowlands 1987)
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Texture-Coefficient (Howarth & Rowlands 1987)
Relationship between texturecoefficient and UCS
Relationship between texture coefficient and TBM performance
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Texture-Coefficient (Howarth & Rowlands 1987)
Texture coefficient of igneous and sedimentary rocks
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Texture-Coefficient (Howarth & Rowlands 1987)
Relationship between texture coefficient and UCS of 9 different metamorphicrock types (50 samples): no correlation for metamorphic rocks!
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Intergranular microcracks
(quartz, Biotite)
Intragranular microcracks
quartz, feldspar, biotite, chlorite
Microcracks
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Rock
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Disintegration of rock by inter- und intragranular microcracks
QU quartz FSP feldspar
GR garnet BI biotite
CHL chlorite
GR
QU
FSP
BIBI
BI
FSP CHL
QU
Microcracks
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Example thin section photograph, traced grain boundaries and microcrack traces pattern.
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Rock
Klima, Schubert
Rock (Micro-) Fabric:Elements, Terms Symmetry
transgranularcrack
intergrain, multigrain crack
multigrain microcrack
transecting one or more grains
intergranularcrack
grain-bounderymicrocrack
grain-bounderymicrocrack
between two grains
intragranularcrack
intragrain, cleavage, transgranularcrack
intragranularmicrocrack
inside one grain
Terms used in fractographicstudies (e.g., Monoto et al., 1981)
Terms used in geological studies (e.g., Richter and Simmons, 1976; Kranz1983)
Proposed termPosition of the microcrack
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Short Course Singapore 2011
Rock
Klima, SchubertX
Y
Z
Schematic Microcrack Orientation and DistributionExample
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
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Klima, Schubert
in particular the microcrack pattern is responsible for the regular divisibility of apparently massive rock, e. g. marbles for utilization as dimension stones
Microfabric,
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Pore size distribution of gneisses, cummulative [cm3/g]
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Pore size distribution of gneisses, -dV/dlogD [c3/g]
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Klima, Schubert
Characterization of Intact Rock:
Abrasiveness
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Short Course Singapore 2011
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Klima, Schubert
Quartz Equivalent Proportion
0,1553Carbonate
31,05total
1,32334Phyllosilicate
5,581831Feldspar
24,0024100Quartz
Example:
Proportion [%]
Rosival-abrasion-hardness
Mineral
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Klima, Schubert
Abrasiveness of Sedimentary rocks(FSCHIM )
[mm] mean diameter of quartz grains
V [%] Quartz equivalent proportion
[MPa] Brazilian tensile strength
Schimazek & Knatz 1970
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Klima, Schubert
CERCHAR-Abrasiveness-Test
• The abrasiveness of intact rock or rock mass affects the wear behaviour of drilling, cutting and milling tools.
• Abrasiveness of rocks depends on different parameters (e.g. structure and texture, equivalent quartz content, Young’s modulus)
• CERCHAR-Abrasiveness-Test is a common testing procedure for the prediction of tool wear due to the fast measurement process and the cheapness.
• The only formal description of this test is the French Standard AFNOR, NF P94-430-1 (2000)
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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CERCHAR-Abrasiveness-Test
„West-Apparatus“(1989) at Graz, University of Technology, Institute of Applied Geosciences, [1] weight, [2] steel pin, [3] vise, [4] rock sample, [5] hand crank
Sample-specimens
steel-styli
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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CERCHAR-Abrasiveness-Index (CAI)
Worn steel stylus tip under the microscope (right picture: 90° rotated)
CAI = d*10
d : diameter of worn stylus dip [mm]
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Klima, Schubert
Cerchar-Classification-Scheme(CERCHAR, 1986)
extremely abrasive4,0 - 6,0
very abrasive2,0 - 4,0
medium abrasiveness to abrasive1,0 - 2,0
slightly abrasive0,5 - 1,0
not very abrasive0,3 - 0,5
ClassificationCAI
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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CAI of some rocks
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Klima, Schubert
Abrasiveness 0.1 mm
Mohs‘scale
Relation between Mohs‘ hardness grade and steel point abrasiveness test value
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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MLPC ABROY Abrasion Meter500 g of crushed rock in the grain size range of 4 - 6.3 mm is placed in the container and the vane is rotated at 4,500 rpm for 5 minutes.The vane suffers abrasion and resulting loss of mass. The quantity of abraded vane metal is then correlated to rock abrasiveness.
French Standard AFNOR, NF P18-579 (1990)
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Qualitatively estimate of the durability of weak rocksSlake Durability Test (ASTM D4644)
Type I: Retained specimen remain virtually unchanged
Type II: Retained specimen consist of large and small fragments.
Type III: Retained specimen is exclusively small fragments.
Calculating the slake durability Index 2nd circle):
B = mass of drum plus oven-dried specimen before 1st circle [g]
WF = mass of drum plus oven-dried specimen retained after the 2nd circle [g]
C = mass of drum [g]
Id(2) = [(WF – C) / (B – C)] x 100
Id(2) = [(WF – C) / (B – C)] x 100
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Short Course Singapore 2011
Rock
Klima, Schubert
Qualitatively estimate of the durability of weak
rocks Slake Durability Test (ASTM D4644)
< 30< 60Very Low Durabiliy
30 – 6060 – 85Low Durability
60 – 8585 – 95Medium Durability
85 – 9595 – 98Medium High Durability
95 – 9898 – 99High Durability
> 98> 99Very High Durability
% retainedafter 2 cycles
% retainedafter 1 cycle
Group Name
Gambles´ Slake Durability Classification (Goodman 1980)
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INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Klima, Schubert
Swelling
Swelling of the ground is a time dependant volume
increase, which is caused by physical-chemical
reactions of rock and water, leading to inward
movement of the tunnel perimeter.
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Klima, Schubert
• Swelling by capillary adsorption
• Swelling by osmosis
• Swelling by hydration of interlayer cations
(swellable clay minerals, e.g., smectite)
• Swelling by formations of new crystal structures
(e.g., anhydrite + water = gypsum)
Stress-Relief - Physico-Chemical Effects Involving Water
Swelling
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• Stress relief leads to a modification of the inter- or
intra-particle stresses which in turn facilitates flow and
ad/absorption of water
• Stress relief causes fissures which in turn facilitate flow
of water
• Water addition causes modification (increase) of inter
(intra) particle distances and this in turn affects the
stresses
Swelling
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• Water content changes increase pore water pressure
from an originally negative to a smaller negative or to a
positive value
• Fissuring or breaking of diagenetic bonds during
shrinkage facilitates flow and modifies original stresses
which in turn facilitates interparticle or intraparticle
addition of water
• Indirect effect: Shearing (e.g. of faults) breaks
diagenetic bonds and increases the exposed surface
areas
Swelling
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Klima, Schubert
Swelling
INSTITUTE FOR ROCK MECHANICS AND TUNNELING
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Klima, Schubert
Basic Elements of Silicate Structure
Swelling
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Swelling
Crystalline Structure of swellable Smectite
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Huder-Amberg-graph
Swelling
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Clay – content [%]
Swelling-pressure[MPa]
Swelling-pressure of clayey anhydrite depending on clay-content, after 600 days
Swelling
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Swelling