Presentation-Rock Mechanics.pdf

7/30/2019 Presentation-Rock Mechanics.pdf

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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?

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