presentation-rock mechanics.pdf
TRANSCRIPT
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Lectures on Rock Mechanics
SARVESH CHANDRA
ProfessorDepartment of Civil Engineering
Indian Institute of Technology KanpurKANPUR, 208016 India
email: [email protected]
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INTRODUCTION
What is RockMechanics?
Rock mechanics is a
discipline that uses the
principles ofmechanics to
describe the behaviour of
rockof engineering scale.
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Rock Mechanics Problems
How will rock react when put to mens use?
What is the bearing capacity of rock on surface an atdepths?
What is the shear strength of rocks?
What is the response of rocks under dynamic /
earthquake type loading? What is the modulus of elasticity of rock and how to get
it?
What are the effects of rock defects (jointing beddingplanes, schistocity, fissures, cavities and otherdiscontinuities) on its strength?
What are the mechanisms of failure of rocks?
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Rock as a Construction Material
For laying structural foundations to support
structures For constructing Underground openings
For protecting slopes
For supporting railway tracks Ballasts
As base and sub-base for roads and runways
As aggregate in concrete Making facia for buildings.
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Geologic
TimeScale
Era Period Epoch Time Boundaries
(Years Ago)
Holocene - RecentQuaternary 10,000
Pleistocene2 millionPliocene5 million
Cenozoic Miocene26 million
Tertiary Oligocene38 million
Eocene54 million
Paleocene 65 millionCretaceous
130 millionMesozoic Jurassic
185 millionTriassic
230 millionPermian
265 millionPennsylvanianCarboniferous 310 million
Mississippian355 million
Paleozoic Devonian413 million
Silurian425 million
Ordovician 475 millionCambrian
570 million
Precambrian 3.9 billion
Earth Beginning 4.7 billionGreenland
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What are we calling a rock?
Grade Description Lithology Excavation Foundations
VI Soil Some organic content,no original structure
May need to
save and re-use
Unsuitable
V Completelyweathered
Decomposed soil, someremnant structure
Scrape Assess by soiltesting
IV Highlyweathered Partly changed to soil,soil > rock Scrape NBcorestones Variable andunreliable
III Moderatelyweathered
Partly changes to soil,rock > soil
Rip Good for mostsmall structures
II Slightlyweathered
Increased fractures andmineral staining
Blast Good foranything exceptlarge dams
I Fresh rock Clean rock Blast Sound
Engineering classification of weathered rock
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Primary Rock Types by Geologic
Origin
Grain
Aspects
Clastic Carbonate Foliated Massive Intrusive Extrusive
Coarse Conglomerate
Breccia
Limestone
Conglomerate
Gneiss Marble Pegmatite
Granite
VolcanicBreccia
Medium Sandstone
Siltsone
Limestone
Chalk
Schist
Phyllite
Quartzite Diorite
Diabase
Tuff
Fine Shale
Mudstone
CalcareousMudstone
Slate Amphibolite Rhyotite Basalt
Obsidian
Sedimentary Types Metaphorphic Igneous Types
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Index Properties of Intact Rock
Specific Gravity of Solids, Gs
Unit Weight,
Porosity, n
Ultrasonic Velocities (Vp and Vs)
Compressive Strength, qu
Tensile Strength, T0
Elastic Modulus, ER
(at 50% of qu
)
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Specific Gravity of Rock Minerals
0 1 2 3 4 5 6 7 8
Specific Gravity of Solids, Gs
halite
gypsum
serpentine
quartz
feldspar
chlorite
calcite
dolomite
olivine
barite
pyrite
galena
Reference Value
(fresh water)
Common Minerals
Average Gs = 2.70
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Unit Weights of Rocks
14
16
18
20
22
24
26
28
0.0 0.1 0.2 0.3 0.4 0.5 0.6
Porosity, n
SaturatedUnitWeight,
T(kN/m3)
Dolostone GraniteGraywacke LimestoneMudstone SiltstoneSandstone Tuff
sat =water [ Gs(1-n) + n]
Gs =
2.80
2.652.50
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eo ogc appng o oc ass
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eo ogc appng o oc assFeatures
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Q tit ti Cl ifi ti f R k
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Quantitative Classification of Rock
Mass Description of J oints:
Orientation, Persistence, Roughness, WallStrength, Aperture, Filling, Seepage,
Number of sets, Block size, spacing.ISRM commissions report
Classification of Rock Material
Based on Uniaxial Compressive Strength
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Uniaxial Compressive
Strength
Ranges for some
Common RockMaterial
Term Kg/cm2
Very Weak- VW
Weak- W
Medium Strong-MS
Strong- S
Very Strong- VS
< 70
70-200
200-700
700-1400
> 1400
Schist, Silt stoneVW-W, SandStone, Lime stone
VW-M,Granite,Basalt, Gneiss,Quartzite, Marble
MS-VS
|
Classification for Rock Material
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Classification for Rock MaterialStrength
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Intact Rock Classification Rock Type
Geologic Formation and Age Indices:
Specific Gravity, Porosity, Unit Weight,Wave Velocities
Strength (compressive, tensile, shear)
Elastic Modulus
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Site investigation boreholes
Percussion drilling soils/soft clay rocks
core recovery
Rotary coring soil or rock >100m deep
core recovery
Rock probing rotary percussion rig
soil or rock no core recovery
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Cable (percussion) rig
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Shell
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Rotary rig
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Core bit
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Core drilling
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Rock core
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How to correlate the properties of rock studied inthe laboratory with in-situ properties?
What in-situ test methods will provide actual in-situ conditions and properties of rock?
What design parameters are to be used for rockslope design?
How to stabilize slopes and undergroundopenings?