Department of Civil Engineering

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IMPORTANT INDIAN ROCKS AS SEEN IN THE FIELD, HAND

SPECIMEN AND UNDER MICROSCOPE

CE – 215, 293, 296, 427, 635

PROF. M. MASROOR ALAM

Department of Civil Engineering

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GRANITE WITH EUHEDRAL CRYSTAL

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SHALE of BIJAWAR GROUP 2.5 – 1.6 Ga, Lalitpur, UP

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Loosely

Compacted

Sandstone

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Well

Compacted

Sandstone

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Silica Cemented Sandstone

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EVAPORITE

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Shelly –

Siliclastic

Limestone

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Coralline

Limestone

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Quartzite

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Gneiss

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Marble

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Schist

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Slate

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Nainital

Slate

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WEATHERING AND ITS EFFECT ON ROCK MASS PROPERTIES

CE - 427

PROF. M. MASROOR ALAM

Department of Civil Engineering

Referred: Tony Waltham, F G Bell, Bhawani and Singh, T Ramamurthi, IS Codes

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CIVIL ENGINEERING

• Civil Engineering works are carried out on or in the ground.

• The properties are characterization of founding ground is significant

• Strength of soil and rocks are of gradation in between is important

• Knowledge of immediate geomorphological and geological processes

• Site investigation where civil engineers encounter geology, involves interpretation of ground conditions “often from minimal evidences”

• Some times 3-D thinking and recognition of potential geo-hazards

• Unforeseen ground conditions can still occur as geology can be infinitely variable

• Civil Engineering design can accommodate almost any ground conditions if correctly assessed and understood

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EARTH IS AN ACTIVE PLANET

• Land surface: Mainly undergo weathering, erosion and rock

destruction

• Sea Bed: Mainly accommodates sediment by deposition (Basin)

• Underground: Rocks are under stress, Get Deformed and New

rocks form

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Geological processes continually modify the earth surface

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Weather and Erode out exposed rocks

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Create apron of sediment on the earth surface

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Add to the complexity of the ground conditions

• All rocks are not “Terra Firma”, Unstable ground does exist

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ENGINEERING RESPONSE TO GEOLOGICAL CONDITIONS

• Difficult ground conditions are found in Flood Plains, Soft Sediments, Deep Rockhead, Unstable Slopes, Old Mines, Shafts, Backfilled Quarry (Brown Fields)

• Soft Ground and Settlement – Foundation Design, Redistribute Load

• Weak Ground – Ground Improvement, Cavity Filling

• Potential Hazard - Avoid Hazard Zone

• Unstable Slope – Strengthen the Slope or Avoid the Hazard Zone

• Severe River or Coastal Erosion – Rock or Concrete Defences

• Potential Volcanic Hazard – Delimit the Hazard Zone, Eruption Prediction

• Potential Earthquake Hazard – Structural Design to withstand Vibrations

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WEATHERING AND SOIL

Top few meters of ground generally consist of soil, drift and weathered rocks with engineering properties varying greatly with bed rock.

SOIL: Mixture of weathered mineral debris and organic material with plant rich top soil and clay rich subsoil. May be Insitu < 1m to > 10m or Transported < 5m to > 500m. Strength less than 0.6 Mpa.

DRIFT: Transported superficial sediments deposited on the bedrock, assorted mix of clay, silt, sand and angular gravel by glaciers.

Colluvium: Slope debris and scree moving under the influence of

gravity, very loosely packed/compacted often shows Quick Sand Cond.

Rockhead: The buried drift/rock interface a conspicuous boundary amongst weak soil, drift, weathered rocks and fresh rocks. Having

different underground sloping pattern unrelated to the present ground profile.

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WEATHERING

• PHYSICAL: Unloading Joints,

Thermal Expansion and Contraction, Insolation, Frost Shattering,

Wetting and Drying, Salt Crystallization.

• CHEMICAL: Solution, Leaching,

• Reduction, Oxidation, Hydrolysis

• BIOLOGICAL: Root Action, Organic Solutions, Boring

• Presence of water enhances all kind of weathering

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DEGREE OF WEATHERING (ISRM, Gupta & Rao)

𝑹𝑹𝑹𝑹 % = σ 𝒄𝒄𝒄𝒄 𝒘𝒘𝒘𝒘𝒘𝒘𝒘𝒘𝒘𝒘𝒘𝒘𝒘𝒘𝒘𝒘𝒘𝒘

σ 𝒄𝒄𝒄𝒄 𝒇𝒇𝒘𝒘𝒘𝒘𝑹𝑹𝒘𝒘 𝒙𝒙 𝟏𝟏𝟏𝟏𝟏𝟏

• CLASS DEGREE OF WEATHERING Rs (%)

• W0 Fresh 0 100 – 80

• W1 Slightly <25 80 – 50

• W2 Moderately 25 - 50 50 – 25

• W3 Highly 50 - 75 25 – 10

• W4 Completely > 75 10 – 01

• W5 Residual Soil 100 < 01

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CLASS W0

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CLASS W0 - W1

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CLASS W1

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CLASS W1

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CLASS 1

CLASS W0

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CLASS W2

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CLASS W3

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CLASS W2

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CLASS W3

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CLASS W4

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CLASS W2

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CLASS W5 – W2

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CLASS W5

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CLASS W5

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