geol chp2 2(new)

8/4/2019 Geol Chp2 2(New)

1/44

MAWAW 17533 : ADVANCED ROCK MECHANICSDVANCED ROCK MECHANICS& ENGINEERING GEOLOGYENGINEERING GEOLOGYENGINEERING GEOLOGY

Chapter 1.0: Introduction to engineering geology

Chapter 2.0: Rock classification

Igneous rocksSedimentary rocks

Metamorphic rocks

Chapter 3.0: Weathering & soils

Chapter 4.0: Geological structures &discontinuities in rock.

Chapter 5.0: Ground Investigation.


2/44

Table 2.4: Rock classification [Waltham, 2002].

ROCK

FAMILY

IGNEOUS SEDIMENTARY METAMORPHIC

Material

origin

Crystalline from

molten magma

Erosional debris on

Earths surface

Altered by heat

and/or pressure

Environment In earth crust; & as

lava flow

Deposition basins;

mainly sea

Mostly deep inside

mountain chains

Rock

texture

Mosaic of

interlocking crystals

Mostly granular and

cemented

Mosaic of

interlocking crystalsRock

structure

Non-bedded

(structureless)

Layered, bedding

planes

Crystal orientation

due to pressure

Rock

strength

Uniform high strength Variable, low; planar

weaknesses

Variable high; planar

weaknesses

Major types Granite, basalt,

pumice

Sandstone, limestone,

shale

Schist, slate, gneiss,

quatzite


3/44

Sedimentary Rocks:Surface processes are essential for the formation of

sedimentary rocks.

Sediment is largely material derived from the

weathering of rocks on the earths surface.All rocks weather on exposure to atmosphere

(water & air), & slowly breaks down to form in situ

soils weathering processes.

The land is essentially the erosional environment; it

is the source of sediments, which forms the

temporary soils before being transported away.


4/44

Land as erosional environment rocks are being weathered to

sediments & transported to depositional environment


5/44

Surface processes:The sea is essentially the depositional

environment, sediment is buried beneath

subsequent layers, & eventually forms most of the

sedimentary rocks.

In most land environments, the in situsoils

subsequently transported away from its source, &

may then be as sediment; this include the solid

debris particles & material in solution in water.Natural transport processes are dominated by

water (river & sea) glaciers & wind.


6/44

Sea as depositional environment transported sediments are

gradually being deposited when the energy of the transportation

agents starts to weaken


7/44

Granite rock is weathered to granitic residual soils

(a sediment consist of gravel, sand & clays) & will

eventually transported & deposited in suitable

depositional areas (river beds, beaches & oceans)


8/44

Surface processes:Transportation agent like water can sort &

selectively deposits it sediment load (boulders,

gravels, sands, silts & clays).

Ultimately all sediment is deposited, mostly in thesea, & mostly as stratified layers/beds.

Burial of this loose & unconsolidated sediment, by

more layers of material subsequently deposited on

top, eventually turns it into sedimentary rock, by thevarious process of lithification.


9/44

Environm ent of deposition of clastic sedim entary

rocks


10/44

Lithification:

Lithification a process by which a weak loose

sediment is turned into a stronger sedimentaryrock. The results of litihification, notably theincrease in strength, are referred to asconsolidation.

3 main processes of lithification are:Cementation, by cement matrix like silica

(strongest), iron oxides, calcite & clay (weakest).

Recrystallisation, small scale solution &

deposition of mineralsCompaction, restructuring & change of grain

packing with decreasing volume.


11/44

Void spaces, shape & grain size of sedimentary rock. This is

similar to cementing of sand & gravel by OPC as in concrete. The

presence of cement matrix reduces the void spaces.


12/44

Depositional structures in sedimentary rock


13/44

Table 2.8: Rock classification [Waltham, 2002].

SEDIMENTARY MATERIALS. Most sedimentary rocks are varieties of

sandstone, clays/shales & limestone.

Mineral grains: mostly quartz, also muscovite (the physically

& chemically stable minerals.

Rock fracgments & volcanic debris (not yet broken down to

their constituent minerals).

SANDSTONES

Breakdown products: clay minerals (fromed by reaction of

water with feldspar or mafic minerals).

CLAYS &

SHALES

Organic debris: plant material to form peat & coal (animalsoft parts form oil).

minor rocks

Organic debris: dominated by clacite from marine shell

debris.

Solutes: dominantly calcite precipated from sea water

largely due to biological activity.

LIMESTONES

Solutes: including gypsum & salt & other less abundant

soluble compounds.

minor rocks


14/44

Classification of sedimentary rocks:

Depending on mode of origin, are divided into:CLASTIC & NON-CLASTIC. The non-clastic can furtherclassified as CARBONATE (organic) & NON-CARBONATE (chemical).

Clastic Sedimentary rock can be sub-divided basedon size of mineral grains:

Rudaceous: grain size > 2 mm.

Arenaceous: grain size 2mm 0.06 mm.

Argillaceous: grain size < 0.06 mm.

Common clastic sedimentary rocks areconglomerate, breccia, sandstone, siltstone, shale& mudstone.


15/44

Table 2.9: Classification of sedimentary rock [Waltham, 2002]

A. CLASTIC SEDIMENTARY ROCKS B. NON-CLASTIC SEDIMENTARY ROCKS

1. RUDACEOUS: coarse grained

Grain size > 2 mm.

Conglomerate rounded fragments.

Breccia angular fragments.

1. CARBONATES (Organic)

Consisting mainly of clacite.

Limestone & allied rocks.

2. ARENACEOUS: medium grained

Grain size between 0.06 2 mm.

Sandstone & allied rocks.

3. ARGILLACEOUS: fine grained

Grain size < 0.06 mm.

Siltstone quartz particles.

Shales, clays, mudstone & allied rock.

2. NON-CARBONATES (chemical)

Flint & chert nodular or banded silica.Coal & lignite lithified peat & plant

material.

Ironstone any iron-rich sedimentary

rock; sand, clay or oolite texture.

Salt & gypsum monomineralic rocks

deposited by evaporation of water.


16/44

Table 2.10: Classification of sedimentary rocks (more detailed)


17/44

Conglom erate clastic sedim entary rock (grainsize > 2 mm, rudaceous)


18/44

Sandstone clastic sedim entary rock (grain size 0.06 2 mm, arenaceous)


19/44

Siltstone clastic sedim entary rock (grain size >

0.06 m m , arenaceous (argillaceous?))


20/44

Shale clastic sedim entary rock (grain size < 0.06

m m , argillaceous)


21/44

Coquina (a type of limestone) consist s of cemented

m arine shell fragm ents


22/44


Carbonate (organic) sedimentary rocks originatesfrom deposits of organic materials (plants, animals

bones & shells.

Coal & peat is sediments originates from

accumulation of plants & vegetations in swampy

environment.

Deposits of iron produces sedimentary rocks rich in

Fe, example magnetite.


23/44

Magnetite organic sedimentary rock


24/44


Deposition & accumulation of siliceous materials(e.g. coral) leads to formation of chert & limestone.

Accumulation of calcareous materials (remnants of

organism) produces chalk & dolomite.

Accumulation phosphoric materials like guano

(tahi kelawar) produces phosphate.


25/44

Chert organic sedimentary rock


26/44

Limestone organic sedimentary rock (calcareous)


27/44

Dolomite organic sedimentary rock (calcareous)


28/44

Coal organic sedimentary rock (carbonaceous)


29/44

Graphite organic sedimentary rock (carbonaceous)


30/44

Successive stages in the formation of high grade coal - anthracite


31/44


Non-carbonate (chemical) sedimentary rocks areformed in depositional environment where

chemical processes like precipitation &

concentration of mineral solution can take place.

Example high rate of evaporation of sea water in

protected beaches (e.g. existing of lagoon &

sandbars) will produce rock salt (Na Cl).

Common non-carbonate sedimentary rocks aregypsum, chloride, limonite & hematite.


32/44

Hematite non-carbonate (chemical) sedimentary

rock (concentration of Fe)


33/44

Gypsum non-carbonate (chemical) sedimentary rock

(concentration of sulphate)


34/44

Limonite non-carbonate (chemical) sedimentary rock

(concentration of Fe)


35/44

Cross-section of London Basin shows varieties of

sedimentary rock, each with different engineering

problem


36/44

Sedimentary rocks:Most common sedimentary rocks are limestone,

sandstone, mudstone & shale.

Limestone:Type is sedimentary, organic or chemical carbonate.

Grains are variable sized calcite mosaic, usually

with shell fragments.

Mineral content mainly calcite 95%, dolomite 3% &

clay minerals 2%.


37/44

Limestone:

Soluble in rainwater, leaving minimal or no soil(solid debris, like sand & clay), and allowing

formation of open fissures, sink holes & caves.

Forms distinctive karst landscape with underground

drainage.

Older limestone are more completely recrystallised

& stronger; UCS 20 - 100 MPa, SBP 0.4 - 4 MPa.

As foundations it is extremely variable; strong rockwith fissures & cavities. May shear along thin shale

bed.


38/44

Topographic view of granite hills


39/44

Topographic view of limestone hills


40/44

Limestone:

Valuable dimension & aggregate stones, burn withclay to make cement.

Varieties include oolite, chalk & dolomite.

Sandstone:

Type is sedimentary, clastic, arenaceous.

Mineralogy consists medium grained with sand

grains mostly of quartz, set in cement of quartz

(siliceous), calcite, clay & other minerals.


41/44

Sandstone:

Mineralogy mainly quartz 80%, clay minerals 10% &others 10%.

Weathering strength; mainly crumbled to sand,

forming sandy well-drained soils.Older sandstones tend to be better cemented &

stronger. Clay cements are notably weak; quartz

cement are generally strong. UCS 10 90 MPa,

SBP 1 4 MPa.

As foundation it is generally strong material, unless

poorly cemented or with weak cement.


42/44

Sandstone:

Value: most sandstones abrade too easily for use asaggregate; some may yield good dimension stone.

Varieties include grit, greywacke & tuff.

Mudstone (clay):

Sedimentary, clastic, argillaceous.Texture is fine grained structureless mass of clay

minerals.

Mineralogy: illite 60%, kaolinite 20%, smectite 10%.


43/44

Clay:

Weathering: reverts to mud forming heavy clay soils.Older, more lithified & unweathered clays have

higher strength. Younger clays have propertiestransitional to those of low strength soils. UCS 1

20 MPa, SBP 0.1 1 MPa.As foundation it is weak material with low, variable

strength depending on water content; prone to slowcreep & plastic deformation; high potential

compaction may cause high & differentialsettlement under structural load.

Value: watertight fill, bricks & cement.

Varieties: mudstone, shale, marl & siltstone.


44/44

Environment of deposition of sedimentary rocksclearly shown the varieties of rocks that may beformed, that are different in terms of types, texture

& properties. These changes may take place in avery short distance (vertically & horizontally).

These changes must be understood beforestructures are constructed in/on sedimentary

rocks, so that appropriate design, method ofconstruction & any ground improvement can beimplemented.

Changes in types of sedimentary rock can be abrupt

(vertically & horizontally) thus, a structure canstand on more than one rock type.

London Basin is typical example.

geol chp2 2(new)

Documents