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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
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8
Grand Coulee Dam onColumbia river
http://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
http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Water%20Resource%20Engg/pdf/m4l04.pdf
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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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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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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
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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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http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Water%20Resource%20Engg/pdf/m4l05.pdf
Reservoir StorageCapacity
http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Water%20Resource%20Engg/pdf/m4l05.pdfhttp://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Water%20Resource%20Engg/pdf/m4l05.pdfhttp://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Water%20Resource%20Engg/pdf/m4l05.pdfhttp://nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Water%20Resource%20Engg/pdf/m4l05.pdf5/24/2018 Geological Considerations in Civil Engineering
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Influence of rock types
Influence of geological structures
Influence of water table
Reservoir silting
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Geological considerations
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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
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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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Geological considerations
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
67
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
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