Engineering considerations
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Engineering Considerations for Geologic Structures ENGINEERING GEOLOGY
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Transcript of Engineering considerations
Engineering Considerations for Geologic Structures
ENGINEERING GEOLOGY
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Effects and Civil Engineering Importance of:
o Foldso Faultso Joints o Unconformities
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1. Effects of Folding
o Change in attitudeo Shattering of rocks
o Weak in strength parameterso Porous and pervious in nature
o Strained nature
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Importance in Civil Engineering
1. Location of dams
2. Location of reservoirs
3. Location of tunnels
4. Quarrying
5. Ground water occurrence
6. Laying roads and railway tracks along hill slopes
7. Oil, gas and ore deposits
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1. Location of Dams2. Location of Reservoirs
1. Dam on upstream dipping beds
2. Dam on horizontal beds
3. Dam on downstream dipping beds
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Case 1: Dam on upstream dipping beds
Chenna Kesavulu
Downstream side
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Case 2: Dam on horizontal beds
Chenna Kesavulu
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Case 3: Dam on downstream dipping beds
Chenna Kesavulu
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3. Location of Tunnels
o Folded rocks are greatly strained, their removal, for tunneling can cause rock explosions
o Along crests of folds, the rocks are in tension, therefore highly unstable
o Along the troughs, rocks are highly compressed, hence tough, offer greater resistance to excavation for tunneling
o Tunneling can be done along the limbs
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Effects of Folding on Tunneling
Parbin Singh
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4. Quarrying
Should be done along the limbs:o Better quality of rocks availableo Fractures associated with crests and
troughs are absent along the limbso Seepage problems along the crests and
troughs can be avoided
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5. Ground water Occurrence
o Synclines often furnish excellent conditions to tap ground water
o Artesian wells and springs originate from synclines
o Fractures present in folded strata act as channels for ground water movement
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6. Roads and Railway tracks along hill slopes
o Ground stability depends on the mutual relation of the dip of the beds and the slope of the cutting
o If the surface slope and the dip are in opposite directions, the ground is stable
o If the surface slope and the dip collide, the ground is unstable
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Stable and Unstable slopes
Chenna Kesavulu
Unstable Stable
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7. Oil, Gas and Ore deposits
o Oil and gas deposits are often associated with anticlines
o Suitable cap rocks, are also an essential requirement
o Crests of folds offer convenient places for the occurrence of ore deposits
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Oil & gas occurrence in anticline
Oil, gas and ore deposits
Ore deposits in anticline
Chenna Kesavulu
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2. Effects of Faulting
o Fracture and shattering of rocks along fault zones
o Serves as pathways for water, causes leakage
o Fault zone lubricated with water are potential sites for further movements
o Gouge and breccia causes problemso Faults bring together, different rocks,
hence homogeneity is lost
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Faulting considerations
o What are the effects of faulting on the rocks in the site?
o Is it possible to build safe structures, with or without ground treatment?
o What is the factor of safety to be adopted, if there is no alternative available?
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1. Location of dams
2. Location of reservoirs
3. Location of tunnels
4. Quarrying
5. Ground water occurrence
6. Laying roads and railway tracks along hill slopes
7. Oil, gas and ore deposits
Importance in Civil Engineering
20Chenna Kesavulu
1. Faults at dam site
Upstream side
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2. Location of reservoirs
o Faults cause leakage of water, if present in the reservoir basin
o Downstream dipping faults cause excess uplift pressure
o Fault zone occurring in the upstream of the river, leads to erosion and accelerated reservoir silting
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3. Location of Tunnels
o Faults zones, being heavily fractured, makes tunneling unstable
o Ground water associated problems are likely to occur
o Renewed faulting can lead to ground displacement
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4. Quarrying
o Quarrying in fault zones produce inferior materials, quantitatively and qualitatively5. Roads & Railway tracks along
slopes
o Fault zones are highly undesirable for construction of roads and railway, due to the possibility of landslides
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6. Ground water occurrence
o Faults zones, being heavily fractured, makes provides space for storage of ground water and permits their movement 7. Ore minerals
o Faults zones, are often rich in mineralso They favor different process that
eventually lead to mineral formation
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Construction in faulted regions
1. Ascertain the presence of faults, their type, nature, extent and effects
2. Study the seismic history of the region
3. Introduce a factor of safety in the design
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o Sources of weakness in rocks, pathways for seepage of water
o Jointed rocks, lubricated by the presence of water, are susceptible to motion
o Joints are usually treated by groutingo Only a well jointed and porous rock can
become a good aquifer or an oil and gas reservoir
3. Effects of Joints
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1. Location of dams and reservoirs
2. Occurrence of landslides
3. Quarrying
4. Tunneling
Importance in Civil Engineering
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o Too many joints in a site, will render it unsuitable for construction of dams
o They act as avenues for serious leakage of water
o Upstream dipping joints are less harmful
1. Location of dams and reservoirs
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o Landslides take place, when the surface slope of the hills and the dip of the beds are in the same direction
o Joints facilitate the heavy percolation of water
o This water comes in contact with clayey material below the ground, producing fine lubricating materials, which causes the slipping of over lying rocks
2. Occurrence of Landslides
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o Depending on conditions, joints can play a helpful or harmful role in quarrying
o Joints cut in situ rocks, which can be easily extracted, without the use of explosives
o Too many joints, on the other hand, render quarrying useless, due to excessive decay of rocks
3. Quarrying
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o Joints can severely hamper the strength of rocks
o They may cause rocks to fall from the roof of the tunnel
o Joints can cause the ground to be saturated with water, decreasing the strength of the rocks
o They may act as sites for the development of solution cavities in limestone terrain
4. Tunneling
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4. Engineering considerations for Unconformities
o They allow the percolation of watero Unconformity indicates a break in the
sequence of rocks, and hence, their engineering properties
o Hence, exhaustive studies have to be done, to analyze the mechanical properties of rocks in the vicinity of an unconformity
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