geological considerations in civil engineering

5/24/2018 Geological Considerations in Civil Engineering

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Geological Considerations In

Civil Engineering

Engineering Geology


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Considerations for:

Selection of site for dams

Selection of site for reservoirs

Construction of tunnels

Construction of mountain roads

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Selection of site for dams

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Need for dams

For hydroelectric power generation For irrigation purposes

To obtain water for domestic and industrial

purposes

For fighting draughts and controlling floods

For navigational facilitiesAdditional benefits include development of

fisheries, tourism etc

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Types of Dams

On the basis of design:

o Gravity dams

o Buttress dams

o Arch dams

o Earth dams

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1. Gravity dam

A solid concrete or masonry structures, thatwithstands the water pressure, by virtue of its

weight

All forces acting on the dam are assumed to

be directly transmitted to the foundation rocks

They are generally of triangular profile andare among the safest

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Concrete GravityDam

http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Water%20Resource%20Engg/pdf/m4l04.pdf
http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Water%20Resource%20Engg/pdf/m4l04.pdfhttp://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Water%20Resource%20Engg/pdf/m4l04.pdfhttp://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Water%20Resource%20Engg/pdf/m4l04.pdfhttp://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Water%20Resource%20Engg/pdf/m4l04.pdf


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8

Grand Coulee Dam onColumbia river

http://en.wikipedia.org/wiki/Grand_Coulee_Dam
http://en.wikipedia.org/wiki/Grand_Coulee_Damhttp://en.wikipedia.org/wiki/Grand_Coulee_Damhttp://en.wikipedia.org/wiki/Grand_Coulee_Dam


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2. Buttress dam

They have a continuous upstream face,supported at regular intervals, by buttress

walls on the downstream side

They are lighter than solid dams

Likely to induce greater stresses at the

foundation, since most of the load passesthrough the buttress walls and is not spread

uniformly over the foundation

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Buttress dam



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Buttress Dam on Lower ColoradoRegion

simscience.org


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3. Arch dam

Arch-shaped, convex at the upstream side

Major portion of the thrust forces acting on

the dam are transmitted by arch action, onto

the abutment rocks

Structural efficiency is higher than that of

gravity dams, the presence of sound abutments

is a prime necessity

Uses less amount of concrete

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13

Idukki Dam

panoramio.com


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4. Earth dam

Non-rigid structures, built with naturally

available materials such as earth and rock

Ideal, where the dam site is weak to support

concrete dams, or where competent rocks arefound at great depths

14Homogenous, with toe drain Homogenous, with chimney drain


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15

Hirakud Dam, across the Mahanadi, Orissa

panoramio.com


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Forces acting on a dam

Self weight

Water pressure

Uplift pressure

Earthquake forces

Other forces due to silt, wave and ice

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Geological considerations

Narrow river valley

Occurrence of bedrock at shallow depth

Competent rocks to offer stable foundation

Proper geologic structures

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1. Narrow river valley

Narrow valley means smaller dam is required,

and hence, lower costs

Defective valleys include:

o Deceptive narrowing due to thick superficial

deposits

o Narrowing due to rock outcrops

o Presence of soluble material like gypsum,

renders the rocks unsuitable

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Some defective narrow river valleys

Chenna Kesavulu


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2. Occurrence of bedrock at shallow depth

The presence of strong bedrock near thesurface, reduces the cost of the foundation

The site should be explore using electrical

resistivity or seismic refraction methods, to

assess the nature of the bedrock

The presence of buried river valleys, huge

boulders gives rise to problems, as they are

composed of lose material

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3. Competent rocks for stable foundation

Igneous rocks are safer than sedimentary ones

Suitability of site depends on:

The existing rock type

The extent of weathering undergone

The extent of fracturing

The occurrence of geological structures

The mode and number of rock types

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4. Proper geologic structures

Undisturbed strata Disturbed strata

Tilted beds

Folded strata

Faulted strata

Jointed strata

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Undisturbed strata

Chenna Kesavulu

Gravity dam on horizontal beds


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24Chenna Kesavulu

Dam on beds inclined in the upstream direction

Gentle inclination Steep inclination


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Dam on beds inclined in the downstream direction

Gentle inclination Steep inclination

Chenna Kesavulu


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26Chenna Kesavulu

Dam over vertical beds


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27Chenna Kesavulu

Dam over folded beds


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28Chenna Kesavulu

Dam over faulted beds


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Selection of site for Reservoirs

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Gibson Reservoir, Montana

http://en.wikipedia.org/wiki/Gibson_Reservoir
http://en.wikipedia.org/wiki/Gibson_Reservoirhttp://en.wikipedia.org/wiki/Gibson_Reservoirhttp://en.wikipedia.org/wiki/Gibson_Reservoir


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Categorization of Reservoirs

Storage and conservation reservoirs

Flood control reservoirs

Distribution reservoirs

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Storage Capacity of a Reservoir

Storage capacity is expressed in terms of:

o Useful storage

o Dead storage

o Surcharge storage

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Reservoir StorageCapacity


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Influence of rock types

Influence of geological structures

Influence of water table

Reservoir silting

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1. Influence of rock types

Igneous rocks such as granites are less porous,

hence will afford more stability

Sedimentary rocks are often porous, but are

more abundant than igneous ones

Metamorphic rocks like gneisses behave like

granites

The nature of rocks are important, as theydetermine the leakage of water through the

foundations

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2. Influence of geological structures

Downstream dip of bedding planes, contribute

to loss of water, development of uplift

pressure

Water can leak through a tilted permeablebed extending to a lower valley

In certain cases, folding and faulting of the

strata can prevent leakage of water

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I li d b d d l k t i it


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37Chenna Kesavulu

Inclined beds and leakage at reservoir sites

Leakage at reservoir sites due to geological structure


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38Chenna Kesavulu

Leakage at reservoir sites due to geological structure


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3. Influence of water table

Position of the water-table is the singlemost factor influencing the leakage of

reservoir water. Rivers can be of:

o Effluent nature

o Influent nature

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I fl f t t bl


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Influence of water table

Chenna Kesavulu

l


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Reservoir silting

Deposition of sediments by rivers, gradually

reduces the capacity of the reservoirs

Silting can be controlled by:

Growing vegetation on loose soil

Covering weak zones with slabs

Constructing retaining walls

Diversion of sediment loaded waters

Silt outlets

Check dams and settling basins41


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Construction of tunnels

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Purposes of Tunneling

For facilitating rail and road traffic

For public utilities

For power generation

For mining activities

For diverting water during dam construction

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T l b i hi


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Tunnel boring machine

http://en.wikipedia.org/wiki/File:Tunnel_Boring_Machine_(Yucca_Mt).jpg
http://en.wikipedia.org/wiki/File:Tunnel_Boring_Machine_(Yucca_Mt).jpghttp://en.wikipedia.org/wiki/File:Tunnel_Boring_Machine_(Yucca_Mt).jpg


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Objects of Geological investigations

Selection of tunnel alignment

Selection of excavation method

Selection of tunnel design

Assessment of cost and stability

Assessment of environmental hazards

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Geological profile along the tunnel axis

Includes information regarding:

o Location and depth of exploratory bore holes

o Types of rocks and their characteristics

o Structure of the rocks

o Hydrological conditions

o Ground temperature conditions

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47Parbin Singh

Geological Profile

F k i t ll ti f t l li i


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Formwork installation for tunnel lining


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Types of rocks Geological structures

Ground water conditions

Overbreak

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1 Types of rocks


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1. Types of rocks

Igneous rocks

Competent, but difficult to work with

Do not require lining

Sedimentary rocks

Less competent, compared to igneous

Sandstones, shales etc are soft, easy to work

Requires lining

Metamorphic rocks

Gneisses are similar to granites 50


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2. Geological structures

Effect of joints Effect of faults

Effect of folds

Effect of undisturbed or tilted strata

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52Chenna Kesavulu

Tunnels in relation to joints, faults and shear zones

Joints parallel to tunnel axis Joints perpendicular to tunnel axis

T l ll l h i f f ld


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53Chenna Kesavulu

Tunnels parallel to the axis of fold

T l di l t th i f f ld


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54Chenna Kesavulu

Tunnels perpendicular to the axis of fold

T l thi k i li d h i t l b d


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55Chenna Kesavulu

Tunnels on thick, inclined or horizontal beds

T l l i li d b d


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Tunnels along inclined beds

Tunnel along strike ofinclined bed

Tunnel along dip of inclinedbed

Chenna Kesavulu


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3. Ground water conditions

Tunnel axis passing entirely through imperviousformations

Tunnel axis mostly above the water table

Tunnel axis below the water table

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4 Overbreak


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4. Overbreak

Tunneling through hard rocks requires the removal

of some rocks outside the proposed perimeter

This excess quantity of rock removed, is called

the overbreak

Geological factors governing the amount of

overbreak are:

The nature of the rocks

Orientation of the joints

Orientation of bedding planes58

Overbreak


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Overbreak

Cases where overbreak is lessChenna Kesavulu

O b k ( td)


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Overbreak (contd)

Cases where overbreak is more

Chenna Kesavulu


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Construction of roads

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A road in Vietnam, 1900m above msl


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62rickmann-uk.com

,

I fl f G l i l f


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Influence of Geological factors

Topography Lithological characters

Consolidated hard rock

Unconsolidated material

Geological structures

Weathering

Groundwater conditions

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Geological structures


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g

Road cut parallel to dip Road cut parallel to strike

Beds dip into the hill - safe

Chenna Kesavulu

Geological structures & weathering


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Joint sets inclined towardsfree face

g g

Unequal weathering causingrock fall

Chenna Kesavulu

C li d i f d i


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Complicated regions for road construction

Hilly areas - meandering

Marshy regions - subsidence

Waterlogged areas capillary action

Permafrost regions blanket action

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Geological problems after road


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Geological problems after roadconstruction

Frost action

Replacing the porous soil

Lowering the water table Erosion problems

Provision of interception ditches

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R f


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Parbin Singh, Engineering and General Geology, S KKataria & Sons

Chenna Kesavulu, N, Textbook of Engineering Geology,

MacMillan India

Thompson, G R and J Turk, Introduction to Physical

Geology, Thomson Brooks/Cole

Reference

geological considerations in civil engineering

Documents

buttress damhttp

buttress damthey

buttress walls

arch dam archshaped

dams selection of site

solid concrete

solid dams

water pressure