soil mechanics & site surveying

8/12/2019 Soil Mechanics & Site Surveying

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1. The Origin of the Earth

Based on observational facts cosmologist have developed classes of hypothesis which try to explain theorigin of the earth. One of them is The Big Bang Theory. At 13.7 billion years ago, the entirety of ouruniverse was compressed into the confines of an atomic nucleus. Known as a singularity, this is themoment before creation when space and time did not exist. According to the prevailing cosmologicalmodels that explain our universe, an ineffable explosion, trillions of degrees in temperature on anymeasurement scale, that was infinitely dense, created not only fundamental subatomic particles and thusmatter and energy but space and time itself. Cosmology theorists combined with the observations of theirastronomy colleagues have been able to reconstruct the primordial chronology of events known as thebig bang.

Figure 1 The Big Bang Theory

2. Major Structural Units of Earth

The constituents of Earth are separated and segregated into layers according to density. The densermaterials are concentrated near the center, the less dense near the surface.The internal layers are recognized on the basis of composition and physical properties.Composition layers are:


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Crust

Mantle

Core

Layers based on physical properties are:

Lithosphere

Asthenosphere Mesosphere

Core

Table 1 Layers of the Earth Based on Composition

OuterCrust

Outer layer of the Earth, extending from solid surface down to the first major discontinuity inseismic wave velocity in the lithosphere. Thickness of crust varies from about 8 km under theoceans to about 35 km under the continents.There are two kinds of earth crust classified according to two different kinds of rock they containedwhere each with its own general composition, thickness and density.(a) Continent Crust: 35 - 60 km thick

relatively low density

granitic rockaverage density: 2.8 g/cm3(b) Oceanic Crust : thickness rarely exceed 5 km

denser materialbasaltic compositionaverage density: 2.9 g/cm3

Mantle

The next major compositional layer of the Earth which covers the core and this zone constitute82% of its volume and 68% of mass of the Earth (Earth largest layer).The mantle has a property called "plasticity" (where a solid has the ability to flow like a liquid). Youmight call the mantle "partially molten". Remember that the temperature of the mantle increasesthe deeper you go. This difference in temperature causes CONVECTION CURRENTS to form.This type of current forms when hot things rise and cooler things sink. These convection currentstumble throughout the mantle. They cause the Lithospheric plates floating on the mantle to movearound. These currents cause our continents and oceans to change location slightly each year.The currents are the driving force for Plate Tectonics or Continental Drift, which we will discuss inmore detail in a later section.The forces which drive continental drift seem to come from the mantle. The hot rock, which boilsup at mid-ocean ridges, comes from the upper mantle. This rock spreads out forming new oceanicplates.When these meet the continents they plunge back down into the mantle, sometimes going downas far as the outer core.In addition there are hot spots, which start at the outer core and rise up through the mantle to formislands such as Hawaii or Iceland.The mantle is composed of iron and magnesium silicate rock, and it goes down to about 2900 kmfrom surface of Earth.

Average density: 4.5 g/cm3Outer

Core

It is speculated that the thickness is about 2250 km and it is made of molten iron and nickel.

Average density: 10.7 g/cm3InnerCore

The thickness' is about 1300 km and probably consists of mostly iron and nickel.Average density: 17.0 g/cm3


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Figure 2: The Lithosphere Figure 3: The layer of Lithosphere and Asthenosphere

Figure 4 The Convection Currents in the Mantle

Figure 5 The Outer Core and The Inner Core


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Table 2 Internal layers of the Earth based on Physical Properties

Lithosphere(rock sphere)

The top of the asthenosphere is about 100 km below the surface. Above the asthenosphere,the material is solid, strong and rigid. This layer is called lithosphere. Contains thecontinental crust of the uppermost part of the mantle.

Asthenosphere

(weak sphere)

A major zone within the upper mantle where temperature and pressure are just the rightbalance so that part of the material melts. The rocks lose much of their strength and

become soft plastic and easily deformed. The asthenosphere is the part of the mantle thatflows and moves the plates of the Earth.The thickness is about 200 km.

MesosphereThe rock below the asthenosphere is stronger and more rigid than the asthenospherebecause the high pressure at this depth offsets the effect of high temperature. The regionbetween the asthenosphere and the core-mantle boundary is called the mesosphere.

Core

The core of the Earth marks a change in both physical properties and composition. It iscomposed mostly of iron and is therefore distinctly different from the silicate (rocky) materialabove. On the basis of physical properties, the core has two distinct parts - a solid inner coreand liquid outer core. Heat loss from the core and the rotation of the Earth probably causesthe liquid outer core to circulate and generate the Earth's magnetic field.

3. The Structure of Earth

Continents and ocean basins are the principle surface features of the Earth. Both are distinctly different incomposition, density, rock type, structure and origin.

(a) Continental MassesThis part of the earth covers about 29% of the earths surface and has an average elevation of abou t 5km above the floors of the ocean basins and about 1 km above sea level. It composed largely of rocksknown as granite. The continents rise above the ocean basins as large platforms. The highest mountainon the continental surface is Mount Everest which is 29000 feet above sea level but the deepest part ofthe ocean is about 35000 feet below sea level at Pacific Ocean.

(b) Ocean BasinsThe greatest part of the hydrosphere is the ocean basin which covers about 70% of the earth's surface.

The ocean floors are also as irregular and possess many deep trenches and mountain ranges as thecontinental masses. The rocks of the ocean are rather dense, dark basaltic rock.

Figure 6 A graph of the Elevation of the Continents and Ocean Basins


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4. The Geologic Processes that Change the Earth's Structure

Geologic Forces: Earth has undergone great changes over million of years. Generally processes ofgradation, tectonism and volcanism.

(a) GradationDegradation: Erosion results from wearing of rocks by water, air and ice.Aggradation: Deposition results in accumulation of sediment and ultimate building up of rock strata.

(b) TectonismPlate tectonics is a dynamic process of the lithospheric plate which moves over a weak plastic layer in theupper mantle known as asthenosphere. These plates interact with one another along their boundaries.Indicative of crustal instability, produce faulting (fracture and displacement), folding, subsidence and upliftof rock formation. Responsible for formation of mountain ranges.Earths lithosphere is composed of seven large plates (Figure 1.19) with thickness ranging from 75 to 125km.

Table 3 Earths Lithosphere Plates

(c) VolcanismA volcano is a vent in the earth's crust through which molten rock materials within the earth, lavas, ashes,steam and gas are ejected and responsible for the formation of plutonic rocks, once solidified at greatdepth. Majority of volcanoes are located along the margins of tectonic plates.

Figure 7 Major Plates of the Lithosphere

Pacific Plate Eurasian Plate

Antartic Plate North America Plate

Indian Plate South American PlateAfrician Plate 20 other small plates in between


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5. Rock

Figure 8 Rock Cycles

Rock is defined as a mixture formed of aggregates of one or more minerals (aggregate of minerals).Rocks can be formed by many different processes.Some are formed from:

(1) Crystallization of a melts (Igneous)magma (intrusive) and lava (extrusive)(2) Solidifying sediments like sand or clay (Sedimentary)(3) Re-crystallizing previously formed rocks in the solid state (Metamorphic)(4) Some are formed by crystallization from hot aqueous fluids (Hydrothermal)

a. Rocks that are formed by crystallization of a melt are igneous. These may be formed at depth(intrusive or plutonic), or they may form on the surface (extrusive or volcanic). In general, igneousrocks that cool rapidly (i.e. volcanic rocks) are very fine-grained; whereas rocks that cool slowly (i.e.plutonic rocks) are coarse-grained.

b. Rocks that are formed on the surface of the earth by solidification (lithification) of weathered ordissolved material are sedimentary. These are generally classified by the size of the particles,although the compositions change systematically with particle size.


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c. Rocks that form by recrystallization in the solid state are metamorphic. They may be metamorphosedfrom sedimentary, igneous, metamorphic, or hydrothermal rocks.

d. Rocks that form by crystallization from hot aqueous fluids are hydrothermal. These are commonlyformed near intrusive igneous bodies. This is a very efficient way to concentrate the elements of lownatural abundance, so many of the economically important ore minerals are formed this way.

Figure 9 Igneous Rock

5.1 IGNEOUS ROCKS

Defined as rocks which are normally crystalline in nature having solidified from an original molten state or

magma that exists for long period of time beneath the surface of earth.

Igneous rocks can be derived from the cooling of molten magma or of lava from volcanic eruption and are

also called fire rocks that are formed either underground or above ground (Figure 3.2 and 3.3).

Underground, they are formed when the melted rock, called magma, deep within the earth becomes

trapped in small pockets. As these pockets of magma cool slowly underground, the magma becomes

igneous rocks (Intrusive). Igneous rocks are also formed when volcanoes erupt, causing the magma to

rise above the earth's surface. When magma appears above the earth, it is called lava. Igneous rocks are

formed as the lava cools above the ground (Extrusive).

Frequently regarded as the parent material because they are the first product to be formed from the

cooling of magma. MAGMA is molten rock material generated in the certain zones deep inside the earth's

crust and possible in the upper zones of the mantle. Magma is believed to exist essentially in a viscous

fluid state and has a tendency to move under external influence of varying hydrostatic pressures and thus

becomes mobile. It moves from deeper zones to higher zones of the crust through forceful injections into

fractures and faults in the adjacent rocks or by process of assimilation of the surrounding rocks thus

changing its composition in the process.


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Figure 10: Underground Figure 11: Above Ground

a. Magma

Magma is hot molten mobile rock (mixture of liquid rock, crystals, and gas). Igneous rocks form whenmagma cools and solidifies. Magmas come out of active volcanoes as lavas. The most abundant magma

is a melt of silicate composition and this can carry suspended crystals and gases which bubble out in air.It is a mixture of liquid rock, crystals, and gas. Characterized by a wide range of chemical compositions,with high temperature, and properties of a liquid.Magmas are less dense than surrounding rocks, and will therefore move upward. If magma makes it tothe surface it will erupt and later crystallize to form an extrusive or volcanic rock. If it crystallizes before itreaches the surface it will form an igneous rock at depth called a plutonic or intrusive igneous rock.Because cooling of the magma takes place at a different rate, the crystals that form and theirinterrelationship (texture) exhibit different properties.

Table 4 Composition of Magma

Magma TypeSolidifiedVolcanic

Rock

SolidifiedPlutonic

Rock

ChemicalComposition

Tempe-rature

ViscosityGas

Content

Basaltic Basalt Gabbro45-55 SiO2%, highin Fe, Mg, Ca, low

in K, Na

1000 -1200 oC

Low Low

Andesitic Andesite Diorite55-65 SiO2%,

intermediate in Fe,Mg, Ca, Na, K

800 - 1000oC

Inter-mediateInter-

mediate

Rhyolitic Rhyolite Granite65-75 SiO2%, lowin Fe, Mg, Ca, high

in K, Na

650 - 800oC

High High

As magma cools, minerals crystallize at different temperatures. There are relatively few minerals whichare important in the formation of igneous rocks. This is because the magma from which the mineralscrystallize is rich in only certain elements: silicon, oxygen, aluminium, sodium, potassium, calcium, iron,

and magnesium.

b. Eruption of Magma

When magmas reach the surface of the Earth they erupt from a vent and it may erupt explosively or

non-explosively.

Non-explosive eruptions are favored by low gas content and low viscosity magmas (basaltic to

andesitic magmas).


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Usually begin with fire fountains due to release of dissolved gases.

Produce lava flows on surface.

Produce Pillow lavas if erupted beneath water.

Explosive eruptions are favored by high gas content and high viscosity (andesitic to rhyolitic

magmas).

Expansion of gas bubbles is resisted by high viscosity of magma - results in building of pressure . High pressure in gas bubbles causes the bubbles to burst when reaching the low pressure at the

Earth's surface.

Bursting of bubbles fragments the magma into pyroclasts andtephra (ash).

Cloud of gas and tephra rises above volcano to produce an eruption columnthat can rise up to 45

km into the atmosphere.

Figure 12 Tephra that falls from Figure 13 If eruption column collapses athe eruption column produces a pyroclastic flow may occur, wherein gas and tephratephra fall deposit rush down the flanks of the volcano at high speed.

This is the most dangerous type of volcaniceruption. The deposits that are produced are calledignimbrites

c. Classification of Igneous Rocks

There are various ways of classifying igneous rocks. The most significant are mineralogical and chemical

composition and rock texture (geological environment). Igneous rocks are either formed as Intrusive or

Extrusive Rocks.The most important distinction in igneous rocks is texture, which is related to the size and shape of theconstituent crystallite grains. Igneous rocks have distinctive textures, characterized mostly by theinterlocking grains that grow from cooling magma. In Igneous rocks, the cooling history and environment

is the function of the formation of textures. Magmas located deep within the Earth's crust cools slowly andthus the individual minerals grains may grow. In contrast, lava extruded at the Earth's surface coolsrapidly, where mineral grains do not have time togrow, therefore cannot be seen without the aid of amicroscope. The rocks appear massive and structureless.
http://en.wikipedia.org/wiki/Crystallitehttp://en.wikipedia.org/wiki/Crystallite


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Figure 14 Classification Igneous Rocks (texture)

The texture refers to the size, shape and arrangement of the component minerals grains and the clues to

the rock's cooling history. The major textures of igneous rocks are:

i) Phaneritic texture

Individual grains are large enough and visible to naked eye (Figure 3.7).

Grains approximately equal in size, form interlocking mosaic and very coarse.

Developed from magmas that cool slowly and common in intrusive bodies.

Figure 15 Examples of phaneritic rocks; phaneritic texture, consists of large grains and can be seen

unaided


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(ii) Aphanetic texture

Individual crystals are so small and cannot be seen unaided.

Rocks are massive and experienced rapid cooling that there was no sufficient time for the growth

of large crystals.

Characteristic of volcanic rock and some intrusive rocks which lost its heat to the surrounding

country rock.

Figure 16 Aphanetic texture consists of grains too small to be seen without a microscope

(iii) Glassy texture

Similar to ordinary glass. Crystals cannot be discerned in a glassy texture, even when the specimen is viewed under high

magnification e.g. obsidian.

. Fig. 17 A glassy texture develops when molten rock material cools so rapidly

(iv) Porphyritic texture

Larger earlier formed crystals are enclosed by a ground mass of smaller crystals.

Cooling history of magma may begin slowly initially which developed coarse crystals and then

while partly crystallized the magma may move to another environment in which the cooling is

more rapid which precipitate fine crystals around the earlier coarse crystals.

Fig. 18 A hand sample and a thin section of porphyritic aphanitic textured rocks. The porphyriticphaneritic texture results from two stages of cooling.


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(v) Vesicular TextureThis term refers to vesicles (holes, pores, or cavities) within the igneous rock. Vesicles are the result of

gas expansion (bubbles), which often occurs during volcanic eruptions. Pumice and scoria are common

types of vesicular rocks. The image below shows basalt with vesicles, hence the name "vesicular basalt".

Figure 19 Vesicular rocks

d. Formation of Igneous Rocks

Scientists have divided igneous rocks into two broad categories based on where the molten rocksolidified.1) Volcanic orextrusive igneous rocksform when the magma cools and crystallizes on the surface

of the Earth.Extrusive rocks are formed from the violent eruption of volcanoes, fissures or cracks in the earth'scrust. Some materials will be emitted with gaseous extrusions into the atmosphere, where they willcool quickly and eventually fall to the earth's surface as volcanic ash and dust. The main product ofvolcanic action is a lava flow emitted from within the earth as a molten stream which flows oversurface of the existing ground until it solidifies. Extrusive rocks are generally distinguished by theirusual fine-grained texture.

Figure 20 Igneous Extrusive Rocks


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2) Intrusive orplutonic igneous rocksform when the magma crystallizes at depth in the Earth.Intrusive rocks which cool and solidify under pressure and at great depths are usually whollycrystalline in texture, since the conditions of cooling are conducive to crystal formation. Methods ofintrusion are by meltingcrystallization, stopingxenoliths and injection (Figure 3.13). Why do wesee intrusive igneous rocks at the surface of the Earth? The answer is they are exposed by erosionwhich has removed all of the material above the intrusion

Figure 21 Intrusive and Extrusive Igneous Rock Bodies

e. Mineral of Igneous Rock

To correctly classify many igneous rocks it is first necessary to identify the constituent minerals that makeup the rock. Piece of cake you say, I saw most of these minerals when I did the Minerals Exercise or Ihave them in my mineral collection. Well, its not quite that easy. The mineral grains in rocks often look abit different than the larger mineral specimens you see in lab or museum collections. The followingsection is meant to assist you in recognizing common rock forming minerals in igneous rocks. Refer backto it often as you attempt to classify your rock specimens.

Plagioclase Quartz


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Potassium Feldspar Muscovite

Biotite Amphibole

Pyroxene Olivine

f. Type of Igneous Rocks

Granite

Granite characterized by a granular

texture, has feldspar and quartz (at least

20%) as its two most abundant minerals,

and in consequence most granite is light-

colored, Biotite or hornblende or both are

also present in most granite with

accessory apatite, magnetite and

sphene. Granites can be fine, medium or

coarse-grained depending on grain sizesof the essential minerals and porphyritic

or non porphyritic depending on the

absence or presence of phenocrysts

(usually alkali feldspar) and/or muscovite.


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Basalt

Basalt is dark colored (black to medium

grey), fine grained (aphanitic) igneous

rock composed of plagioclase, feldspar,

pyroxene and magnetite with or without

olivine and contain more than 53% by

weight of SiO2. Most basalts are non

porphyritic but some contain phenocrysts

of plagioclase, olivine and pyroxene.

Basalt is the world's most abundant lava

and is very widespread.

Gabbro

Gabbro is dark colored, coarse-grained,

granular basic igneous rock consisting of

essential calcium rich plagioclase,

feldspar (approximately 60% of augite

and orthopyroxene plus or, minus olivine

with accessory magnetite or ilmenite.

Gabbros result from slow crystallization of

magmas of basaltic composition. Gabbro

is widely distributed in both large and

small masses. Dykes and thin sills of fine-

grained gabbro are especially common.

In most of these small intrusions, the

mineral grains are so small that they are

barely recognizable without aid of

microscope. Such gabbros, intermediate

in grain size between basalt and normal

grabbro, are called dolerite.

Diorite

Diorite is an intermediate, coarse-

grained, granular igneous rock with up to

10% quartz, plagioclase and lesser

amount of ferromagnesian minerals. The

most common ferromagnesian minerals

are hornblende, biotite and pyroxene. In

general, diorite masses are much smaller

than those of granites or granodiorite.

Crystallization of

Magma

Crystallization of magma is not a simple

process. An experiment done by

N.L.Bowen (Figure 3.28) in early 1900sdemonstrated that minerals crystallize

sequentially as the temperature drops in

a silicate magma and that solid crystals

can react with the liquid phase of the

magma to form new minerals during the

crystallization process.


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5.2 SEDIMENTARY ROCKS

Sedimentary rocks are the second major rock group. It is formed from fine constituents of rock usuallyfrom mountainous areas which are transported to lower elevation due to certain processes. After travelingat some distance it may get deposited over some existing rocks which on consolidation will result information of what as known as sedimentary rocks. Sedimentary rocks cover about 70% of surface ofcontinents but less than 10% of rocks in the earth's crust and most encountered in construction projects.It contains certain metallic and nonmetallic mineral deposits that are important to humanity e.g. depositsof petroleum and coal.

Figure 22 Sedimentary Rock

The genesis of sedimentary rocks involves four major processes which are:

i. WeatheringWeathering is a number of chemical and mechanical processes that act to break up rocks such asan interaction between rocks exposed at the Earth's surface and elements in the atmosphere. Thepreexisting rocks can disintegrate and decompose either by physically or chemically and forms layerof loose, decayed rock debris or soil. The unconsolidated material can then be transported easily byvarious agents such as streams, wind, groundwater and glaciers. For example, once surface rockshave been broken up into fragments by weathering processes, erosion (by wind and moving water)can transport the detrital material away from its source region to a new location where these newsediments can be deposited.

ii. TransportationRunning water is the most effective form of sediment transport. Large quantities of sediment arecarried towards the sea and deltas are formed from sediment transported by rivers. Wind andglaciers also transport sediment although restricted to certain climatic zones. Sorting that occursduring transportation is an important factor in the genesis of sedimentary rock.Water and air are fluids, thus the size of detrital material that can be transported depends on thevelocity (i.e. energy) of the fluid. In other words, rapidly moving water or air can transport larger grainsize detrital material than more slowly moving water or air. Ice, on the other hand, is a solid. Thus,ice can transport all sizes of sediment independent of the velocity at which the ice is moving. In thecase of transport by water or air, sediments are deposited at locations where the velocity of the fluiddecreases. For example, consider a river flowing out of the mountains into a lake.


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a. Classification of Sedimentary Rocks

Sedimentary rocks are classified according to the derivation of sediment types. The two major sedimenttypes are:

a) Detrital or Clastic Sedimentary RockClastic or detrital sedimentary rocks are made up of mineral grains, fragments of other rocks (calledlithic fragments), shells and other inorganic (hard) of formerly living organisms. The clastic particlesor grains in a sedimentary rock are cemented together by mineral precipitates that form during theprocess of diagenesis (Diagenesis - The increases in temperature and pressure that cause chemicalreactions to occur between the mineral grains of the sediment and the fluids that are trappedbetween the grains thus decrease the amount of interstitial volume between the grains of the rockand finally cementing the grains together).Also known as fragmental sedimentary rocks that are derived from weathering process of parentrocks. The texture of clastic sediments consists of a fragment which varies in shapes and sizes e.g.range of various sandstones with different grain sizes. The strengths of clastic sediments are closelyperforated to their state of consolidation.Clastic or detrital sedimentary rocks formed from mineral grains and rock fragments. Clasticsedimentary rocks are classified according to their texture (grain size). Rocks with gravel size detritalgrains (Grain size greater than 2 mm) are called conglomerates(if the grains have rounded

outlines) or they are called breccias(if the grains are angular in shape). Rocks made up of sandsize grains (Grain size 1/16 to 2 mm) are called sandstones. For sandstone, if it was dominated byquartz grains it will be quartz sandstone(also called quartz arenite), if it was dominated by feldspargrains it will be arkoseand if dominated by sand - sized rock fragment grains it will be lithicsandstone (also called litharenite or graywacke). Silt is called siltstone(Grain size 1/256 to 1/16mm (gritty).Clay with grain size less than 1/256 mm (smooth) are called shale(if fissile) orclaystone(if massive). Mud is technically a mixture of silt and clay. It forms a rock called mudstone(or mud shale if fissile).They have a clastic (broken or fragmental) texture consisting of:i. Clasts (larger pieces, such as sand or gravel)ii. Matrix (mud or fine-grained sediment surrounding the clasts)iii. Cement(the glue that holds it all together), such as: calcite, iron oxide and silica

Clastic sediments are classified based on the grain size, diversity and identities of the detritalmaterials they are made up of the grain size classification.

Figure 23 Clasts and matrix (labeled) and iron oxide cement (reddish brown color)

Figure 24 Conglomerate Figure 55 Breccia


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(a) (b) (c)

Figure 26 (a)Quartz Sandstone (b) Arkose Sandstone (c) Greywacke Sandstone

Figure 27 Siltstone Figure 28 Shale (fissile) Figure 29 Claystone (massive)

Table 5 Types of Sediment and Clastic Sedimentary Rocks

Types of Sediment Clastic Sedimentary Rock

Clays or MudsSilts

SandsGravels

Mudstone or ShaleSiltstone

SandstoneConglomerate or Breccia

Conglomerate

Consist of consolidated deposits of gravel, with variableamounts of sand and mud in the spaces between thelarger grains. Cobbles and pebbles usually are wellrounded fragments over 2 mm in diameter.Conglomerates are accumulated at base of manymountain ranges, in stream channels and on beaches.

Sandstone

Sandstones is most familiar sedimentary rock with sandsize ranging from 0.0625 mm to 2 mm in diameter.Composed of almost any material thus can be variouscolours. Quartz grains are usually the most abundantmineral because quartz is a common constituent inmany other rock types, not easily broken down byabrasion and chemical action. The particles of sand inmost sandstones are cemented by calcite, cilica or ironoxide.

Siltstone

Siltstone is fine-grained in which the material is 0.0625mm to 0.004 mm in diameter (finer than sand but

coarser than mud). Silt is a material frequently carried insuspension by rivers and deposited in floodplains anddeltas.

Shale

Shales (Mudstone) are solidified deposits of mud andclay. The particles that make up the rock are less than0.004 mm in diameter and can be seen undermicroscope. Shale is most abundant in sedimentaryrock, usually soft and easily weathered.


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b. Chemical Sedimentary Rocks

Chemical sedimentary rocks are precipitated from a solution as a result of changing physical conditions ordue to the actions of living organisms. The chemical weathering of rocks also lead to the formation ofsediments as dissolved matter in solutions. Such sediments are usually identified by their chemicalcomposition. Common dissolved sediments include the bicarbonates of Ca, Mg, Na, and K with calciumand magnesium being the most abundant in terms of volume produced.Other sediments include dissolved silica in the form of Si(OH)4, sulphates and chlorides of Na, Mg, Ca,and K. These sedimentary ultimately form sedimentary deposits and sedimentary rocks by two distinctprocesses known as Organic Sedimentary Rocks and Inorganic Chemical Sedimentary Rocks.

(i) Organic Sedimentary RocksThis group consists of rocks composed of organic matter (mainly plant fragments).The most common example is coal, the compacted remains of dead plants that grew in a tropicalswamp environment. It composed of accumulations of organic debris.

(ii) Inorganic Chemical Sedimentary RocksIn organic chemical sediments form by direct precipitation from solution. Typical solutions thatchemical sediments form from include: sea water, fresh surface water in rivers and lakes andgroundwater. One common class of inorganic chemical sedimentary rocks is called evaporites.

Evaporites form by precipitation from sea water or brackish fresh water. The scenario for theformation of an evaporite requires that a batch of sea water becomes isolated from input ofadditional sea water, for example in a lagoon. The isolated sea water then begins to evaporate,which concentrates the dissolved salts and other components of sea water. As evaporationproceeds, various minerals will be precipitated from the water. Minerals that are formed in this wayand are found in evaporites are listed in the Table 3.8. This group includes the evaporites, thecarbonates (limestones and dolostone), and the siliceous rocks. These rocks form within thedepositional basin from chemical components dissolved in the seawater. These chemicals may beremoved from seawater and made into rocks by chemical processes, or with the assistance ofbiological processes (such as shell growth). In some cases it is difficult to sort the two out (incarbonates or some siliceous rocks, for example), so they are grouped together aschemical/biochemical.

Evaporation and precipitation forming salt deposits

Table 6 Inorganic Chemical Sedimentary Rock

Rock Type Composition

LimestoneDolomite

Chert/FlintGypsum

Rock Salt

CaCO3CaMg (CO3)2

SiO2CaSO4.2H2O

NaCI


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c. Type of Sedimentary Rocks

Limestone Most abundant nonclastic rock. Composed principally of mineral calcite, calciumcarbonate (CaCO3) and originates both chemical and organic processes. Manyplants and invertebrate animals extract calcium carbonate (limestone) from waterin their life processes and use it to construct their shells and hard parts of calcite.When these organisms die, their shells build up deposit of limestone with atexture consisting of shells and shell fragments. In quiet water, calcium carbonateis precipated as tiny needlelike crystals, which accumulate on the bottom. Soonafter they are deposited, the grains commonly are modified as they arecompacted and become recrystallised. This modification producesmicrocrystalline limestone, a rock with a dense, very fine grained texture. Itsindividual crystals can be seen under high magnification. Microcrystallinelimestone also is precipitated from springs and from the dripping water in caves.

Dolostone Rock composed of mineral dolomite, a calcium magnesium carbonate(CaMg(CO3)2. It is similar to limestone in most textural and structural features aridappearance. Can develop by direct precipitation from seawater.

Rock Salt andGypsum

Rock salt is composed of mineral halite (NaCI). It forms by evaporation in salinelakes. Gypsum CaSO42H2O also originates from evaporation of saline water.

d. Characteristics of Sedimentary Rocks

Sedimentary rocks are easily recognizable. The proper rock name, origin and depositional environment ofthe sediment that was lithified can be interpreted correctly if carefully observed. It exhibits variety ofdistinctive features such as:

Texture Sedimentary rocks are easily recognizable by its texture,i.e. the arrangement of particles or grains that make upthe rock. There are two main types of texture ofsedimentary rocks:

ClasticThese rocks are composed of aggregates ofindividual mineral or rock fragments. The origin ofthese types of rocks can be described as detritalsince the rock fragments have been eroded,

transported and deposited. Detrital rocks withparticles larger than sand size are calledconglomerate or breccia. Fine grained clastic rocksare called shale or mudstone. Usually shale is easilysplit into thin slabs parallel to the depositionallayering of the sediment.

Non Clastic

These rocks are formed by chemical precipitationfrom aqeous solutions. Both rocks formed either asinorganic and organic process has non clastictexture. E.g. Secretion from organisms thatcomposed of silica or calcium carbonate. However, ifa rock is composed of an accumulation of shells or

fragments of shells, its texture is considered to beclastic. The formations of chemical sedimentaryrocks are usually associated with chemicalprecipitation from water that is responsible fordeposits of limestone, dolomite, salt and gypsum.This process is common in sea water but also occursin lakes, streams, caves (groundwater) and springs.The most common type of limestone is those ofmarine deposits.


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SedimentaryStructures

These are characteristic features imparted to the rockduring the processes of sediment transport anddeposition. The most fundamental sedimentary structureis bedding i.e. the stacking of sediments in individuallayers or beds. Differences in the process ofsedimentation can lead to different types of bedding.Three main types of bedding are:

i) Rhythmic LayeringAlternating parallel layers having different properties.Sometimes caused by seasonal changes indeposition (Varves). i.e. lake deposits where thecoarse sediment is deposited in summer months andfine sediment is deposited in the winter when thesurface of the lake is frozen.

ii) Cross beddingSets of beds that are inclined relative to one another.The beds are inclined in the direction that the wind orwater was moving at the time of deposition.Boundaries between sets of cross beds usuallyrepresent an erosional surface. Very common inbeach deposits, sand dunes, and river depositedsediment.

iii) Graded beddingAs current velocity decreases, first the larger or moredense particles are deposited followed by smallerparticles. This results in bedding showing adecrease in grain size from the bottom of the bed tothe top of the bed.

iv) Non - Sorted SedimentSediment showing a mixture of grain sizes resultsfrom such things as rockfalls, debris flows, mudflows,and deposition from melting ice.

Fossils Fossils are remains or evidence of ancient plants andanimals that have been preserved in earth's crust e.g.shell (usually composed of calcium carbonate or silica)and bones (phospatic material) can be preserved forlong periods of time. Soft organic remains can bepreserved in anaerobic environments although they maybe greatly altered from their original state.These environments account for deposits of petroleum,which are derived from the remains of microscopicmarine organisms, and coal, the product of terrestialplants. Fossils which are not necessarily of organicorigin can also be sedimented in the rocks, for examplepetrified wood which composed of silica that has beenprecipitated by groundwater which replaces the organic

material and retaining the original cellular structure.


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Stratigraphy Stratigraphy is the branch of geology that study theorigin of sedimentary rocks which refers to strata (layers)constructed in sedimentary rocks due to the ancientlandforms and depositional environments. Usually eachstratum is separated by bedding plane and the thicknessof the rock and its texture depends on the carrying agente.g. wind, water or ice. Geologic maps and crosssections constructed from stratigraphic studies areuseful in enabling the prediction of the sequence ofrocks that may underlie a particular section.

Color The color often indicates the geochemical environmentat the time of deposition. Rocks formed in anenvironment abundant ofoxygen are usually in shadesof red or brown. The reddish or yellowish colour isimparted by the small amount of ferric iron in an oxidizedstate. Sediments that accumulated in environmentslacking of oxygen are usually darker in colour e.g.somber grey and green shades. Petroleum and coal aregood examples of sediments rich in organic matter andusually the colour will be black. The lack of oxygen is

critical to the preservation of these materials becausebacteria will decompose the organic matter if oxygensupply exists.

Ripple Marksand MudCracks

Ripples are undulations of the sediment surfaceproduced as wind or water moves across sand. Ripplemarks or little waves are usually found at surface ofbeach, sand dunes or bottom of stream. Ripples whichform in unidirectional currents (such as in streams orrivers) tend to be asymmetrical. Crests of asymmetricalripples may be straight, sinuous, or lobe-like, dependingon water velocity. Asymmetrical ripples have a steepslope on the downstream side, and a gentle slope on theupstream side. Because of this unique geometry, its

provide information of the condition under which thesedimentary rocks was originally deposited. Mud cracksare also commonly preserved in sedimentary rock andshow that the sedimentary environment occasionallywas exposed to the air during the time period thesedimentary was deposited. Mud cracks in rockssuggest that the original sediment was deposited inshallow lakes on tidal flats and act as exposed streambanks.

MarineEnvironment

Continental shelf Continental slope and rise (deep sea fans) Abyssal plain Reefs

Transitionalenvironments

Beach and barrier islands Delta Lagoons Estuaries


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5.3 METAMORPHIC ROCK

Metamorphism is the process of changes in texture and mineralogy of pre-existing rock due to changes intemperature and/or pressure. Metamorphic means change of form. The rocks are formed due to thetransformation of pre-existing igneous or sedimentary that has been buried deeply within the crustbecause of the movements of lithospheric plates. These rocks are subjected to changes in thetemperature, pressure and chemical environments inside the earth's crust and thus become unstable.The minerals undergo recrystallization forming new minerals and new rocks either physically orchemically and the texture, color, structure and chemical composition are modified. The processes thatcause these changes are known as metamorphism (meta-change; morphe - form/shape).

Figure 29 Metamorphic Rock

Metamorphism causes changes in texture (recrystallization, alignment of platy minerals) and mineralogy(growth of new minerals that are more stable). The processes of compaction and recrystallization changethe texture of rocks during metamorphism (Table 3.9).

Table 7 Compaction and Recrystallization that change the texture

Process Description

Compaction

The grains move closer together.The rock becomes denser.Porosity is reduced.Example: clay to shale to slate.

Recrystallization

Growth of new crystals. No changes in overall chemistry. New crystalsgrow from the minerals already present. A preferred orientation of mineralscommonly develops under applied pressure. Platy or sheet-like mineralssuch as muscovite and biotite become oriented perpendicular to thedirection of force. This preferred orientation is calledfoliation.

Table 8 Metamorphic Textures

Type Description Example

Foliation A broad term referring to the alignment ofsheet - like minerals.

Schistosityalignment of large mica

flakes, as in a mica schist derived fromthe metamorphism of shale.

Slaty cleavagealignment of very fine-grained micas, as in a slate derived fromthe metamorphism of shale.

Phyllitic structurealignment of fine -grained micas, as in aphyllite.


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Gneissic bandingsegregation of lightand dark minerals into distinct layers inthe rock, as in a gneiss.

Lineation

Refers to the alignment of elongated, rod-like minerals.

Lineation is a texture commonly seen inthe metamorphic rock amphibolitesderived from the metamorphism of basalt.

amphibole, pyroxene, tourmaline, kyanite,etc

Non - foliated orgranular

Those which are composed ofequidimensional grains.There is no preferred orientation. Thegrains form a mosaic

quartz or calcite

Table 9 Mineral changes in Metamorphic Rocks

Process Description Example

RecrystallizationRearrangement of crystal structure ofexisting minerals. Commonly many small

crystals merge to form larger crystals.

Clay in shale becoming micas inslate, phyllite, and schist.

Formation of newminerals

A number of metamorphic minerals whichform during metamorphism and are foundexclusively (or almost exclusively) inmetamorphic rocks

Garnet - dark red dodecahedrons (12sides).Staurolite - brown lozenge -shapedminerals, commonly twinned to form"fairy crosses". State mineral ofGeorgia.

a. Agents of MetamorphismNormal increases in temperature and pressure with depth in the earth are sufficient to initiatemetamorphic activity. The changes occur in order to restore equilibrium in rocks that have beensubjected to new environments. The heat and pressure in deep crustal environments are two maincomponents of metamorphic processes. The principal agents of metamorphism are changes in

temperature, pressure and chemically active solution.

i. TemperatureThe major cause and important agent of metamorphism. The temperature in the crust at a depthof 15 km is approximately 300C. It is noted also that the temperature increases as the depthincrease. This temperature is sufficient for recrystallisation for some minerals to begin. As therock temperature rises, minerals begin to change from solid state to liquid state and amount ofpore fluid in rocks increases. Heat reduces the ability of rock to withstand deformation andincrease the rate of chemical reactions which facilitate the production of new minerals i.e. newatomic arrangement. Heat is provided by the nearby intrusions of magma or associated withcompression of the crust.

ii. PressureThe effect of pressure varies at different depths in the crust. Rocks at shallow depths arerelatively cold and brittle, so they can be altered e.g. fracture or crack when subjected to highpressures. At greater depths, rocks are much softer because of the high temperatures. Underaction of pressure, they tend to deform by plastic flow. In the region of plastic deformation,pressure influences the types of new minerals formed and are more tightly packed atomicstructure and thus has greater density. Pressure is derived from deep below the earth surfaceand also associated with the collision of tectonic plates.


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iii. Chemically Active SolutionRocks that crystallize during the metamorphism does not actually melt but occur in a solid phasestate. The minerals are greatly facilitated by movement of small amounts of liquid or gaseoussolutions through the rock which acts as a medium of transport for ions. These solutions whichtravel through the pores and cracks of the rock add and remove various ions and molecules asthe reactions occur.In this way new chemical constituents can be brought in contact with mineral grains so that theymay diffuse through the mineral structures during recrystallisation. Water may also react assolvent to form another mineral. Water can be derived from:

Entrapped water in parent sedimentary rocks at time of deposition

Large watery liquid and vapors from magma

Small amount of water from hydrous mineral

Table 10 Agents of Metamorphism

Heat Pressure Chemically Active Solution

(a) Frictional sliding of plates

(b) Radioactivity

(c) Gravitational compression

(a) Burial (litho static)

(b)Directed pressuredue to tectonicsm

Water - circulates in response toheat generated by coolingmagmas. Exchanges ionsbetween the solution and therock through which it istravelling.

b. Types of Metamorphism

Basically, there are three types of metamorphism which is (1) Contact metamorphism, (2) Regionalmetamorphism and (3) Dynamic metamorphism.

Type DescriptionCommon effects(assume that there will be newmineral growth with all types)

Example rocktypes

Contact(thermal)

Heating of country rocks

during igneous intrusion orbeneath thick flows.

Growth of new metamorphic

minerals in random orientations. hornfels

Regional

(burial)

Large scale metamorphismcharacteristic of mountain beltsand shield areas as a result oftectonism.

"Subset" of regionalmetamorphism; involves thepost diagenetic, progressivechanges occurring tosedimentary rocks duringburial.

Involves burial to produceelevated pressures andtemperatures controlled by thedepth attained in the crust ormantle and deformation toproduce tectonic fabrics.

Large variety ofrock types,including slates,phyllites, schists,gneisses

DynamicResponse to intense strain andis commonly of localizedoccurrence.

Oriented fabrics, brecciation,granularization.

mylonites, faultbreccias

Hydrothermal

Chemical reactions as a resultof circulation fluids. Commonat sea floor spreading centre.

Metasomatism (change inchemical composition).

skarns

ImpactImpact of large, high velocitymeteorites.

Shock effects producing denseminerals at earths surface whichnormally occur at mantle depths.

Shatter cones,shocked quartz


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c. Classification of Metamorphic RocksThe classification of many metamorphic rocks is based on metamorphic texture which depends oncrystal size and, if present, foliation. Foliated metamorphic rocks are named according to their typeof foliation and any visible minerals which may be present. A rock with a schistose foliation andcontaining significant proportions of garnets and micas might be called garnet-mica schist. A rockwith a gneissic foliation and containing the same minerals as granite may be called a granitic gneiss.Some low-grade metamorphic rocks are named by adding the prefix "meta" to the flame of theirprotolith. For example, a meta-conglomerate is the low grade metamorphic equivalent of aconglomerate.Other metamorphic rocks are named on the basis of mineral composition Marble is a metamorphicrock composed almost entirely of calcite or dolomite. A quartzite is formed by the recrystallization ofsandstone under metamorphic pressures and temperatures and consists mainly of quartz Quartzitecan be distinguished from quartz sandstone by the fact that quartzite breaks through grains whilequartz sandstone breaks between grains.


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5.4 WEATHERING

Weathering is a general term describing all changes that result from the exposure of rock materials to the

atmosphere. It is one of the most important geologic processes that leads to the disintegration or

decomposition of geologic deposits. Weathering occurs because most rocks are in equilibrium with higher

temperatures and pressure deep within the Earth.

Rocks which are deeply buried lies in a different environment physically and chemically than those

exposed on the earth's surface and therefore changes will take place to accommodate these new

conditions. If they are exposed to the much lower temperatures and pressures at the surface, to the

gases in the atmosphere, and to the elements in water, they become unstable and undergo various

chemical changes and mechanical stresses.

As a result, the solid bedrock breaks down into loose, decomposed products. Rock fragments produced

by weathering are removed by erosion and the general term for both weathering and erosion is known as

denudation.There are two classification of weathering processes which is physical and chemical weathering.

Figure 30 Sedimentary rocks in the Valley of the Gods in southern Utah. Notice that the layering inthe rocks is horizontal and that erosion has exposed them in their present form. The red color results fromiron cement in the rocks, which are mostly sandstone.

a. Physical Weathering (Mechanical)

Physical weathering is the mechanical breakdown of the rocks into smaller fragments without undergoinga change in chemical composition. No chemical elements are added to or subtracted from the rock.Physical forces that contribute to this type of weathering are frost action, unloading, saline crystal growth,

alternate heating and cooling, and organic activities.

i. Frost Action

Frost action works best in jointed rock or rocks with fractures in mountainous area with cool climates.

Water that freezes in cracks and pores of rocks at temperature which drops below 0C will result in

an increment of 9% in volume that will create pressure (compressive forces) against the wall of the

fracture eventually widened the cracks.


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Figure 31 Ice Wedging

ii. Unloading / Exfoliation

This is a process of reduction of pressure on underlying rocks by erosion that takes place on the

overburden. The rocks expand as pressure is released and this process is known as unloading. The

response to unloading may cause large joints (sheeting) to develop. The joints tend to be oriented

parallel to the slope of the terrain. Natural erosion of overlying rocks has already induced unloading

stresses in any exposed rocks. Further removal of material by man can create rapid strain.

Figure 32 Sheeting Figure 33 Joint block separation

(a) (b)

Figure 34 (a) Exfoliation occurs when solid rock mass comes apart in series of shells or plates(b) Jointing causes the rock to break up into large blocks

iii. Saline Crystal Growth

Combination of moisture and salts (halite, gypsum, etc.) has been found to cause scaling or decay of

building stones. Stresses due to growth of salt can cause the rock to break apart physically. This

process is particularly effective in porous rocks subjected to alternate wetting and drying. Further

disintegration of rock may occur due to expansion of salt crystals which have grown in former voids.


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iv. Alternate Heating and Cooling

Happens in mountainous regions and deserts where rocks are subjected to drastic change of

temperature. The rock will expand as they are heated during daytime and contract due to freezing

temperature at night. This will lead to cracks and crevices

v. Organic ActivitiesThe activities of plants and animals also promote rock disintegration. Burrowing animals such as

worms, ants and rodents mechanically mix the soil and loose rock particle. Pressure from growing

roots widens cracks and contributes to the rock breakdown.

Figure 35 Ophiomorpha burrow, JKR Quarry, Bintulu - Miri Road Sarawak

b. Spheroidal Weathering

In this type of weathering, a rounded shape is produced because weathering attacks an exposed rock

from all sides at once, and therefore decomposition is more rapid along the corners and edges of the rock

(Figure 4.10). As the decomposed material falls off, the corners become rounded and the block eventually

is reduced to an ellipsoid or a sphere. Exfoliation is a special type of spheroidal weathering, where the

rocks break apart by separation along a series of layers.

(a) (b)

Figure 36 (a) Granular disintegration common in coarse - grained igneous rocks(b) Granular disintegration in sandstone


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Figure 37 Spheroidal Weathering

c. Rates of Weathering

There are few factors which determine the rate at which the exposed bedrock being weathered by various

agents of weathering.

i. Composition of rocks

Mineral and chemical composition is one of the most important factors. Cementing materials(substance holding rock together)

Igneous rocks are resistant to mechanical weathering but more susceptible to chemical

weathering

Sedimentary rocks e.g. dolomites and limestones are decomposed by carbonation and

solution

ii. Physical Condition of rock

Crevices, cracks, holes will allow weathering agents to penetrate and eventually destruct the rock.

iii. Topography

Weathering is rapid where land slopes steeply. Increases in altitude have high rainfall and

temperature will be low. This will eventually increase in the rate of weathering.

iv. Climatic Condition

Climates which have abundance rainfall and moist will accelerate the weathering process

especially chemical weathering. Dry or cold weather are usually apt to physical weathering.

Figure 38 Type and extent of weathering vary with climate


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Table 12 Weathering classification system for sedimentary rocks (Anon, 1977)

Grade Zone Description Remarks

Residual soil VIAll rock material in degraded conditionand original rock structure destroyed

No rock texture completely destroyed

Completely

Weathered V

All rock material in a degraded

condition but original mass structurestill discernible.

Slakes readily in water. Geological pick easily

indents surface when pushed. Coring notpossible by ordinary methods.

HighlyWeathered

IVMore than half of the rock material ina degraded condition

NX size core can be broken and crushed byhand. Rock material plastics does not readilyslake in water

Moderatelyweathered

IIILess than half of the rock material in adegraded condition

Hammer blow makes drumming soundpossessing strength such that NX core(55mm) cannot be broken by hand. Rockmaterial not plastic.

Slightlyweathered

II

Discoloration of discontinuityweathered surfaces and somedegradation material on discontinuitysurface.

Hammer blows give a dull note. Needs morethan one blow of the geological hammer tobreak specimen.

Faintlyweathered

IB Discoloration of major discontinuitysurfaces.

Fresh IA No visible evidence of weathering

Table 13 Weathering profiling of sub surface (Martin and Hencher, 1986)


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6. Site Investigation comprises

a) Planning

The successful design and construction really need prediction data like soil and rockcharacteristics, and groundwater level

Knowledge on geology structure

To obtain that information, engineers and geologists acquires MAP and CROSS SECTIONSUBSURFACEwhich are having the kind of information such as:o Topography contour for pre and post construction.o Top layer of rocks contouro Weathered rocks layer contouro Contour between rock and soil boundaries

b) Desk Study

Study on MAP and REPORTS

Aerial Photo and Remote Sensing

Photographs on color or black and white

c) Investigation on Natural rock or Man Made outcrop

1) Investigation on surface

Test pits and trenches

Adits and Shaft

2) Observation on rock outcrops

Geotechnical mapping on rock exposed

Sampling on jointed rocks.

3) Seismic activities and Faulted

4) Using geophysics methods in SI.

d) Drilling Exploration

Rock core drilling

Core orientation

Supervision and logging

e) Observation into borehole

Camera (TV)

Packer Test

Geophysics

Dilatometer, Pressuremeter


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6.1 Rotary Wash Boring (Borehole)

Figure 39 Schematic diagram Rotary Wash Boring

a. Wash boring

The foremost SI used around the world.

The soil and rock characteristics were recorded into BORELOG(Figure 41 & 42)

Soil samples were taken using spilt barrel meanwhile rock samples obtained using core barrel.

b. Boring Record

Boring logs: Information on subsurface conditions obtained from the boring operation is typicallypresented in the form of a boring log (boring record). A continuous record of the various stratafound at the boring is developed. The contents:

Description/classification of soils and rock type encountered,

changes in strata, water level,

soil consistency,

type and depth of sample and field test.

c. Limitation of Boring Data Providing info on subsurface conditions only at the actual drilling location, interpolation between borings to determine conditions does involve some degree of uncertainty Some limitations inherent to the info shown on typical drillers log:

Drill road casing

Chopping bit Driving shoe

Water jet at high velocity

Suction host

Wash water tub

derrickro e

engine

ressure host


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The employed crews are primarily drilling tradesmen: w/ limited experience in detail soilclassification; have no familiarity w/ the importance of subsurface conditions on thefeatures of building design design and construction.

some importance items of info can be innocently passed over by driller whose majorinterest is in the rate of drilling progress.

Assign technically trained personnel: to examine and classify recovered soils, to directthe depth as which should be taken, to select the drilling sequence, to document factorsrelating to surface and subsurface conditions that could influence on design orconstruction.

6.2 Soil Sampling

Disturbed (but representative):1. Grain size analysis2. Liquid & plastic limit3. Specific gravity4. Organic content5. Classification

Undisturbed:1. Consolidation2. Hydraulic conductivity3. Shear strength

6.3 Rock Sampling

6 meter of core rock length must be obtained for granitic rocks in order to make sure the rockformation is not a BOULDER.

12 meter of core rock length of limestone must be coring to ensure the rock formation is bedrock.(Hinder from cavity, pinnacles, sinkholes or others CARSTIC formation structures resulting frompresent of limestone).

RQD, TCR, SCR and FI must be calculated for geotechnical interpretation.

Rock strength Tests: Uniaxial Compression Test, Triaxial Compression Test, Point Load Test andSchmidt hammer (Strength Test)

6.4 Rock Quality Designation (RQD)

The Rock Quality Designation index (RQD) was developed by Deere (Deere et al 1967) to provide aquantitative estimate of rock mass quality from drill core logs. RQD is defined as the percentage of intactcore pieces longer than 100 mm (4 inches) in the total length of core. The core should be at least NWsize (54.7 mm or 2.15 inches in diameter) and should be drilled with a double-tube core barrel. Thecorrect procedures for measurement of the length of core pieces and the calculation of RQD aresummarized in Figure 7.2.


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Figure 40 Borelog in soil condition


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Figure 41 Borelog shows the core rock logging


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Figure 42 Core Rock Quartz of Mica Schist at Lebuh Raya Simpang Pulai to Cameron Highland

6.5 Detailed Core Logging

Figure 43 Schematic diagram of Rock Core
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6.5.1 Core Logging Calculations

Total Core Recovery (TCR%)= Core Recovered/Length of Core

Solid Core Recovery (SCR%)= Solid core pieces in full diameter/ Length of Core

Rock Quality Designation (RQD%)= Solid Core Pieces > 100mm/Length of Core

Fracture Index (FI/m run)= Number of Fractures/Length of Core

Examples Calculation

TCR = 1.4/1.5 = 93%SCR = 0.18 +0.71 + 0.17/1.5 = 71%RQD = 0.23 + 0.33 + 0.24 + 0.5/1.5 = 63%

6.6 Geophysics

6.6.1 Resistivity

Resisitivity measurements are made by injecting a DC current into the ground through twoelectrodes and measuring the resulting voltage at the surface at two other electrodes.

The depth of measurement is related to electrode spacing.

Resisitivity measures bulk electrical resistivity which is a function of the soil and rock matrix,percentage of saturation and type of pore fluids.

.Figure 44 Resistivity Sounding

Uses:

Resistivity measurements are primary used for soundings to determine depth and thickness ofgeologic strata;

Also can be applied to profiling measurements for locating anomalous geologic conditions,detecting and mapping contaminant plumes, locating buried wastes and mineral exploration;

Can be used for azimuthal measurements to determine fracture orientation.
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Advantages:

Good vertical resolution (sounding);

May also be used for profiling;

Measurements can be easily made to depths of few hundred feet or more;

Various electrode configurations are available for different applications.

Disadvantages:

Requires intrusive contact with the ground;

Station measurements only;

Electrode array can be quite long, with outermost electrode spacing from 9 to 18 times the depthof interest;

Susceptible to interference from nearby metal fences, buried pipes, cables, etc.;

Generally, cannot be used over asphalt or concrete;

Effectiveness decreases at very low resisitivity values (use electromagnetic measurements).

Table 15 List of resistivity value for several rocks and soils. (Keller and chknecht, 1966, Daniels

dan Alberty, 1966)

Material Resistivity 1m Conductivity 1m Igneus& Metamorf

GraniteBasaltSlate

MarbleQuarzite

Sedimentary RockSandstone

Shale

Limestone

Soil and WaterClay

AlluviumGroundwater (Clean)

Marine water

5x10310

6

103-10

6

6x102-4x10

7

102-2.5x10810

2-2x10

8

8-4x103

20-2x103

50-4x102

1-10010-80010-100

0.15

10-6

-2x10-4

10

-6-10

-3

2.5x10-8

-1.7x10-3

4x10

-9-10

-2

5x10-9-10-2

2.5x10-4

-0.1255x10

-4-0.05

2.5x10-3

-0.02

0.01-11.25x10

-3-0.1

0.01-0.16.7


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Figure 45 Application of resistivity survey to determine sinkholes or cavity of limestone


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Figure 46 Application of resistivity survey to determine water boundaries

6.6.2 Seismic Refraction

Seismic refraction measurements are made by measuring the travel time of a refracted seismicwave as it travels from the surface through one layer to another and is refracted back to thesurface where it is picked up by geophones.

Shock or impact is made at a point, seismic waves through the surrounding soil & rock.

The wave speed relating to the density and bonding characteristics of the material.

The velocity is determined.

The magnitude of the velocity is than utilized to identified the material

The travel time of a seismic wave is a function of soil and rock density and hardness.

Figure 47 Seismic refraction wave movement into subsurface


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Uses:

Primary application for seismic refraction is for determination of depth and thickness of geologicstrata, structure and anomalous conditions;

Depth can be calculated under each geophone to produce a detailed two-dimensional top of rockprofile;

Detail is inversely proportional to geophone spacing; If compressional P-wave and shear S-wave velocities are measured, in situ elastic moduli of soil

and rock can be determined;

Can be used for azimuthal measurements to determine fracture orientation;

Also has application for evaluation of man-made structures.

Advantages:

Typical measurements are less than 100 feet but can easily made to greater depths, if necessary;

Can resolve up to 3 to 4 layers;

Can provide depth under each geophone;

Both P and S waves can be determined;

The source of seismic energy can be as simple as 10 pound sledge hammer.

Disadvantages:

The survey line length (source to farthest geophone) may be 4 to 5 times the desired depth ofinvestigation;


Station measurement only;

Sensitive to acoustic noise and vibrations;

Seismic velocity of layers must increase with depth;

Will not detect thin layers or layers with inverted velocities;

Deeper measurements will require explosives as an energy source.

The velocities of the primary (Vp) and secondary (Vs) waves are related to elastic constants anddensity of the medium by equations:

3

4(

GK

Vp

GVs

Where, K = bulk modulus

G = shear modulusP = density

The velocity of the S wave in most rocks is about one half that of the velocity of the P wave.

The S wave is not propagated at all in fluids.


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6.6.3 Seismic Reflection

The seismic reflection technique measures the travel time of seismic waves from the groundsurface downward to a geologic contact where part of the seismic energy is reflected back togeophones at the surface while the rest of the energy continues to the next interface.

The travel time of the seismic wave is a function of soil and rock density and hardness.

Figure 48 Schematic diagram of seismic reflection

Uses:

Primary application is for determination of depth and thickness of geologic strata, structural andanomalous conditions.

Advantages:

Provides a high resolution cross section (as compared to refraction) of soil/rock along profile line;

The high resolution method uses frequencies of up to a few 100 Hz;

Measurements can be made from about 50 feet to a few 1,000 feet deep;

Measurements to these depths can often be made without explosives, often using a 10 poundsledge hammer as a seismic source;

The survey line length (source to farthest geophone) is usually 1 to 2 times the desired depth ofinvestigation (much less than that required for refraction measurements);

Both P and S waves can be measured.

Disadvantages:


Station measurement only;

Sensitive to acoustic noise and vibration;

Can require extensive processing.


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Table 16 Wave velocity in various soils & rock

Type of soil/rock P-wave velocity m/sec

Soil:

Sand, dry silt, fine grained top soil2001 000

Alluvium 5002 000

Compacted clays, clayey gravel, denseclayey sand 1 0002 500

Loess 250 - 750

Rock:

Slate and shale 2 5005 000

Sandstone 1 5005 000

Granite 4 0006 000

Sound limestone 5 00010 000

6.6.4 Gravity

Gravity measurements detect changes in the earth's gravitational field caused by local changes in thedensity of the soil and rock or engineered structures.

.

Figure 49 Sketch of gravity survey over cavity

Uses:

Standard gravity measurements are primarily applied to characterizing geologic structure usingwidely spaced stations (100's to 1,000's of feet apart).

Microgravity measurements can be used to characterize detailed localized geologic conditions(such as bedrock channels, caves, and abandoned tunnels and mines) usually within the upperfew 100 feet. Microgravity uses closely spaced stations (a few feet to about 50 feet) and a microgravimeter (capable of reading to a few microgals).
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Advantages:

Provides a means to characterize conditions in geologic and cultural environments, where othergeophysical methods may fail;

Does not require intrusive ground contact;

Data can be interpreted to provide estimates of depth size and the nature of the anomaly;

Can be used inside buildings and structures.

Disadvantages:

Station measurements only;

Instruments carried by hand only;

Requires base station for drift corrections;

Requires accurate elevation measurements;

The process of making microgravity measurements is a relatively slow and tedious in the fieldand requires extensive processing and corrections;

Susceptible to cultural and natural vibrations.