Engineering considerations

Engineering Considerations for
Geologic Structures
ENGINEERING GEOLOGY

Effects and Civil Engineering
Importance of:
o Folds
o Faults
o Joints
o Unconformities
2

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
3

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
4

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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6
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

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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10
Effects of Folding on Tunneling
Parbin Singh

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
12

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

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
15

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Oil & gas occurrence in
anticline
Oil, gas and ore deposits
Ore deposits in anticline
Chenna Kesavulu

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
17

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
3. Location of tunnels
4. Quarrying
6. Laying roads and railway tracks along hill
slopes
7. Oil, gas and ore deposits
19

20Chenna Kesavulu
1. Faults at dam site
Upstream
side

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 qualitatively
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5. Roads & Railway tracks along slopes
o Fault zones are highly undesirable for
construction of roads and railway, due to the
possibility of landslides

o Faults zones, being heavily fractured, makes
provides space for storage of ground water and
permits their movement
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7. Ore minerals
o Faults zones, are often rich in minerals
o They favor different process that eventually
lead to mineral formation

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
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3. Effects of Joints

1. Location of dams and reservoirs
2. Occurrence of landslides
3. Quarrying
4. Tunneling
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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
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1. Location of dams and reservoirs

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
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2. Occurrence of Landslides

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
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3. Quarrying

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
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4. Tunneling

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
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Engineering considerations

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Engineering considerations