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Engineering Considerations for Geologic Structures
ENGINEERING GEOLOGY
2
Effects and Civil Engineering Importance of:
o Folds
o Faults
o Joints
o Unconformities
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1. Effects of Folding
o Change in attitude
o Shattering of rocks
o Weak in strength parameters
o 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 Dams
2. 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 available
o Fractures associated with crests and
troughs are absent along the limbs
o 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 problems
o 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
movement7. Ore minerals
o Faults zones, are often rich in minerals
o 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 grouting
o 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 water
o 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
Reference
• Parbin Singh, Engineering and General
Geology, S K Kataria & Sons
• Chenna Kesavulu, N, Textbook of Engineering
Geology, MacMillan India
• Reddy, D V, Engineering Geology, Vikas
Publishing House
• Garg, S K, Physical and Engineering Geology,
Khanna Publishers
• Thompson, G R and J Turk, Introduction to
Physical Geology, Thomson Brooks/Cole 33
