Geology of Dams & Reservoirs

GEOLOGY OF DAMS AND RESERVIORS

Types of Dams:
Based on purpose
1. Storage Dam Or Impounding Dam
2. Detention Dam
3. Diversion Dam
4. Coffer Dam

1. STORAGE DAM:
• It is constructed to create a reservoir to store water during
periods when there is huge flow in the river (in excess of
demand) for utilization later during periods of low flow.
• Water stored in the reservoir is used for irrigation, power
generation, water supply etc.

2. DETENTION DAM:
• It is primarily constructed to temporarily detain all or part of the
flood water in a river and to gradually release the stored water
later at controlled rates
• So that the entire region on the downstream side of the dam is
protected from possible damage due to floods.
• It may also be used as a storage dam.

3. DIVERSION DAM:
• It is constructed to divert part of or all the water from a river into
a conduit or a channel.
• For diverting water from a river into an irrigation canal, mostly a
diversion weir is constructed across the river

4. COFFER DAM:
• It is a temporary dam constructed to exclude water from a
specific area.
• It is constructed on the u/s side of the site where a dam is to
be constructed so that the site is dry.
• In this case, it behaves like a diversion dam.

A typical dam has following parts –
• Crest – The top of dam. In some cases, this provides a roadway
or walk way.
• Parapet walls – Low protective walls on the either side of the
road way on the crest.
• Abutments – The valley slopes on the either side of dam wall
to which it is keyed.
• Free board – The space between the highest level of water in
the reservoir and crest of the dam.

• Heel – The upstream portion of the dam in contact with the river
bed or foundations.
• Toe – The downstream portion of the dam wall for the discharge
of surplus water from the reservoir.
• Spillway – The passage in the dam wall for the discharge of
surplus of water from the reservoir.
• Gallery – Level or gently sloping tunnel like passage transverse
or longitudinal within the dam wall with drains in the floor for
seepage water

Based On Structural Behaviour
• Gravity Dam
• Arch Dam
• Buttress Dam
• Embankment Dam

Gravity Dams
• The entire force acting
on dam wall is
transmitted on to small
area of the foundation.
• Therefore, a dam of this
nature is to be selected
only in such places where
very competent and
stable rocks occur.

Buttress Dams
• These are concrete dams in
which there is deck sloping
upstream. This deck which
takes entire load is supported
by buttress , which are further
supported by struts. The
buttress distribute the loads
over a wide area.
• Thus, a even slightly weaker
rocks can be considered as
suitable for this kind of dam.

Arch Dams
• The shape & design of arch
is such that the whole or
greater part of load is
transferred to the abutments.
This means the rock below
the abutments should be
competent and stable. The
modulus of Elasticity of rock
should be high enough.
• Arch Dams are best suited to
narrow, deep, river-cut
gorges.

Earth Dams
• Earth dams are planned in such
places where the underlying
material is too weak to support
masonry dams or where
competent rocks occur at greater
depths. They are built of clay,
sand, gravel etc.,
• Due to greater area of base &
some other factors, the weight
exerted by dam per unit area of
ground will be relatively less.

Geological Considerations in the
Selection of Dam Site
• Narrow River Valley
• Occurrence of Bedrock at a shallow Depths
• Competent rocks to offer Stable Foundations
Suitability of different types of rocks
Influence of weathering
Effect of occurrence of intrusions
Effect of fracturing
• Effect of Associated Geological Structures
• Leakage below Dams

Narrow River Valley
• At proposed dam site, if the river valley is narrow, a
small dam is required which reduces the cost of
construction.
• A Few defects at narrow river valley are as follows
Narrowing of valley due to landslides, rock creep, rock
fracturing, thick superficial deposits such as residual soil,
talus, boulders, silt and clay etc.,
The occurrence of buried river channels crossing the site,
either below or adjacent to river bed.
Unsuitability of rocks due to presence of soluble minerals
like gypsum or due to faulting which may be concealed
beneath sediments.

Occurrence of Bedrock at a shallow
Depths
• Shallower bed rock aims lesser foundation cost
• Bed rock occurs at shallow depths in young rivers
since the sediments deposited in less. The problems
with younger formation is as follows:
This hilly terrains may not provide a suitable
topography for larger reservoir basin
The flow of water may not be high, therefore only
small dams can be constructed
• To know depth of bed rock geophysical investigations
has to be carried out.

Different Common Rocks & their
Competency to offer Stable Foundations
Igneous Rocks
• The massive plutonic & hypabyssal igneous rocks
are most desirable at dam site
• Volcanic rocks which have vesicular &
amygdaloidal are not desirable.
• Massive basalts which are fine grained are
desirable at dam site when they don’t have
vesicular structure.

Sedimentary Rocks
• Shales have slippery base hence undesirable at dam site
• Well Cemented siliceous and ferruginous sandstones are
competent and suitable for dam foundation
• Laterites, limestone & conglomerates are undesirable.
• Thick massive sedimentary formations with less porosity
are desirable.
• Alternating soft and hard rocks of small thickness are
undesirable.

Metamorphic Rocks
• Gneiss unless they posses high degree of foliation and
mica minerals is suitable at a dam site.
• Schist are undesirable
• Quartzite are very hard and highly resistant to weathering.
They are neither porous, nor permeable.
• Marbles even tough compact by virtue of their chemical
composition they are unsuitable at dam site.
• Slates are undesirable as it is soft, weak and have a slaty
cleavage.

Influence of Weathering
• Weathering reduces strength, durability of
rock hence the extent of weathering should be
carefully assessed to ascertain whether a rock
is suitable or unsuitable.
• Dull appearance, faded color and emitting a
dull sound to a hammer blow are some simple
indications of weathering.

Effect of Occurrence of Intrusions
• Black Dolerites and white quartz occurs
frequently as intrusions.
• The intrusive contribute to heterogeneity at
dam site and hence undesirable.
• The contact planes of intrusive serve as weak
plane.
• Grouting can be done at weak planes to
improve the competence of the site.

Effect of fracturing
• Fracturing is common in all rocks, they reduces the
cohesion or compactness of rock.
• Fractures contribute to porosity, permeability of
rocks.
• If the fractures are numerous and if occur in large
areas they should be treated by grouting.
• Beds which are thick, compact, uniform and without
any structural defect are very desirable at dam site.
• Alternating soft and hard beds, when inclined are not
desirable at dam site because slippage of hard bed
over softer one occurs.

Effect of Associated Geological
Structures
• The properties of rock gets modified either advantageously or
disadvantageously when geological structure occurs in rock.
• The various geological structures which are common in nature
are as follows
Horizontal Strata
Beds lie perpendicular to the length of valley
 Tilted Beds
 Vertical Beds
 Beds which are folded
 Faulted Beds
 Beds with joints
 Beds parallel to length of Valley

Beds With Horizontal Strata
• This geological situation is good at the
dam site because the load of the dam
acts perpendicular to the bedding
planes.
• The seepage of water is also prevented
by weight of dam. Thus, uplift
pressure can be reduced.
• If the strata are composed of
alternating hard and soft rocks it shall
be undesirable.

Beds Perpendicular to valley
• Tilted Beds with Gentle Upstream
Dip (10^0-30^0 Inclination)
It is ideal situation for dam
construction.
The resultant force acts more or
less perpendicular to bedding
planes. Hence takes load
effectively.
Any percolated water is directed by
bedding plane to upstream side i.e.,
there is no scope for leakage of
water and uplift pressures.

• Tilted Beds with Steep Upstream
Dip
It is not bad but not as
advantageous as that of previous
case.
There will not any uplift pressure
on dam and no leakage of water
from reservoir.
The resultant load is not
perpendicular to bedding plane
which makes it less competent than
previous case.

• Tilted Beds with Gentle Down
stream Dip
It is very undesirable for dam
location.
The resultant load and bedding
planes are in same direction which
makes it less competent to with
stand forces.
The water in reservoir percolates
with pressure thereby causing uplift
pressure and loss of water.

• Tilted Beds with Steep Down
stream Dip
It is very undesirable for dam
location.
The resultant load and bedding
planes are nearly parallel, which
makes it less competent to with
stand forces.
The Bhakra Dam on the Sutlej, lies
on such undesirable site composed
of sandstone and shale. Suitable
measures are taken to ensure safety.

• Vertical Beds
It will not pose problem of uplift
pressure on dam or leakage of
reservoir.
It will not have advantage interms
of competence of rocks.
The Escales Dam in the Spain, lies
on such site composed of limestone
and cretaceous marl.

• Folded Beds
It is generally less dangerous than faulting.
The folded rocks will be under strains and are also physically
fractured along the crests
Grouting & other precautions have to be considered, to improve
the stability and competence of rocks at site.

• Faulted Beds
It is generally undesirable.
The active faults causes
displacements of the site and
also increases the chances for
occurrence of earthquake.
Faults increases porosity which
aids for water percolation which
intern reduces competence and
causes leakage of reservoir.
If faults occurs in the upstream
with downstream dipping faults
are dangerous.

• Jointed Beds
They contribute to physical weakness of rock and also to
porosity and permeability.
Grouting is used to overcome this defects.

Beds Parallel to length of valley
 There is a danger of slippage of rocks along bedding plane.
 The water from reservoir have a adequate chance to
percolate below the dam which is undesirable.
 The foundation and abutments of dam rests on different
rock which is undesirable.
 It is undesirable for dam construction

SELECTION OF DAM SITE:
Selection of site – The selection of dam site across a river is to
impound water behind the dam. Following points are required
that –
Topographically, a place which is most suitable for the purpose is
selected. Ideally it should be narrow or a small valley with
enough catchment areas available behind so that when a dam is
placed there it would be easily store a calculated volume of
water in reservoir created upstream.
Technically, the site should be as sound as possible, strong,
impermeable and stable. Strong rocks for design, impermeable
for inventory of stored water and stability with references to
seismic failures.

• Constructionally, the site should not be far from deposits of
materials which would be required for construction.
• Economically, the benefits arising out of a dam is proposed to
be placed at a particular site should be realistic and justified in
terms of land irrigated , power generated and water stored i/c
floods averted.

• Geological investigations –
Following geological characters of the area should be
investigated for particular site selected for dam – Geology of
area comprising of main topographical features, natural
drainage patterns, general characters and structures of rock
formations, the trend and type of weathering and erosion of
area.

• Geology of site i.e. types of rocks of the area where dam will be
built, properties of rocks i.e. chemical composition, texture and
hardness of rocks, porosity and permeability of rocks.
• Structural features of the rock i.e. dip, strikes, outcrop etc.
Structural defect of rocks i.e. folds, fissures, faults etc.
• Crushing and shearing strength of rocks, extent of weathering of
rocks.
• Thickness of the bedding planes.
• Zones of fractures and weaknesses.
• Water table in the area

• The ideal foundation should be built over a uniform formation.
• The underlying rocks should be strong enough to bear weight
of dam and to withstand resultant thrust of pressure of the
impounded water and weight of dam itself.

STAGES OF INVESTIGATION IN
SELECTION OF DAM SITE
• Preliminary Investigation
Lithology: It provides details of rock type present, their
nature and extent of weathering, occurrence of rock and
soil debris etc., in that area
Structure: It provides information on strike, dip of beds and
also details of folds, faults, joints and unconformities.
Topography: It provides information on surface features
like valley, hills, trend of river, stability of slope, scope for
occurrence of landslide. The rough assessment of depth of
bed rock
Ground Water Conditions: It provides information on
springs, seepages, wells etc., which provides information
on scope for leakage and present of any cavities.

STAGES OF INVESTIGATION IN
SELECTION OF DAM SITE
• Detailed Investigation
Surface Investigation: preparation of geological map of the
area, Important engg. properties of rocks such as
compressive & tensile strength, porosity, permeability,
durability etc., The details on orientation of bedding
planes, thickness of bedding planes and any intrusions if
present any.
Sub-Surface Investigation : Geo-physical investigations to
know the sub-surface profile. Drilling of bore holes will
gives detailed information on cavities & fractures present
and also helps in verifying the Geo-physical investigations

RESERVIOR:
• A reservoir usually means an
enlarged natural or artificial lake,
storage pond or impoundment
created using a dam to store
water.
• Reservoirs can be created by
controlling a stream that drains an
existing body of water.
• They can also be constructed in
river valleys using a dam.

Purpose of a Reservoir
• Reservoirs may be managed to balance some or all of the
following activities:
Water supply
Flood control
Soil erosion
Environmental management
Hydroelectric power generation
Navigation
Irrigation

Considerations for Successful
Reservoir
• From the Geological point of view, a reservoir can be claimed to be
successful if it is watertight (i.e.. If it does not suffer from any serious
leakage of water) and if it has a long life due to very slow rate of silting in
the reservoir basin.
• The reservoir, when filled, gives chances for reactivation of underlying
inactive faults. This in turn, gives scope for the occurrence of seismicity and
landslides in that region.
• The Success of Reservoir depend on following factors:
 Capacity of Reservoir
 Effect of Evaporation
 Water tightness and influencing factor
 Buried River Channels
 Influence of Rock Types
 Influence of Geological Structures
 Influence of Water Table

• Capacity of the Reservoir: Reservoir capacity depends on the
existing topography and the proposed top water level (TWL)
of the reservoir.
• Effect of Evaporation: The natural process of evaporation
reduces the quantity of water in the reservoir. Through
unwanted, this process is unavoidable. Since reservoirs are
open and extended over larger areas. The magnitude of
evaporation will be extensive. of course, such loss shall be less
if the topography is such that a reservoir covers a small area
but has a great depth to provide adequate capacity.

• Water- Tightness and Influencing factors: When a river
flows over such loose soil or fractured ground, it is natural that
some water of the river percolates (or leaks) underground.
Before the construction of the dam, this leakage shall be less
and limited only to the extent over which the river flow
occurs. But when the dam is constructed, the impounding
water accumulates in large quantity in a reservoir which
covers a very large area. This means percolation occurs over a
large area. Due to the height of the water in reservoir,
significant hydrostatic forces develops which will make the
leakage more effective on the sides and the floor of the
reservoir. Thus, the extent of leakage may become alarmingly
great.

• Buried River Channels: This are frequent in
glaciated regions, and are serious source of leakage.
This is because they are filled with loose and coarse
sediments and these allow heavy leakage.
• Due to presence of buried channel at Tapoban Dam
site of river Dhauli Ganga in UP there is a severe
leakage of reservoir water.

• Influence of Rock Types: Water-tightness of a reservoir basin
is also very much influenced by the kind of rocks that occur at
the reservoir site. If the rock are porous and permeable, they
will cause the leakage of water and hence such rock are
undesirable at the reservoir site.
• Igneous Rocks:
Intrusive igneous rocks like granite, by virtue of their
composition, texture and mode of formation are neither
porous nor permeable. Hence their occurs at the reservoir
site will not cause leakage of water unless they have other
defects like joints, faults, or shear zones.
But the extrusive (i.e.. Volcanic) igneous rocks like basalt
are not desirable because they are often vesicular.
Influence of Rock Types

Sedimentary Rocks
• By virtue of their wide areal extent and frequency of
occurrence, sedimentary rocks are the more important in this
regard than igneous rocks. Among the different sedimentary
rocks shale's are the most abundant followed by sandstone &
limestone.
• Shales the extremely fine grained sedimentary rocks. Are
highly porous but not permeable. For this reason, the
occurrence of shale's at the reservoir site shall not cause any
leakage. Of course, at the dam site, its occurrence is
considered undesirable because of its incompetency and
slippery character.

Sedimentary Rocks
• The Sandstone is an aquifer and hence it has a tendency to cause
leakage. However, careful examination is needed to know
whether it causes severe leakage or not, if present at the reservoir
site. This is so because the porosity and permeability of different
sandstone differ depending on a degree of cementation and
composition of the cementing materials of sandstones.
• The Occurrence of limestone, at the reservoir site is, in general,
undesirable. Of course, it may not only have negligible porosity
but also possess reasonable hardness and durability. Thus
through the compact of massive limestone superficially seem to
be water proof, they may be internally cavernous and cause
profuse leakage.

Metamorphic Rocks
• Gneiss, which is one of the most
common metamorphic rocks, behave
like granite, i.e.. They are neither
porous nor permeable.
• The schists, on the other hand, by
virtue of their excellent foliation and
soft and cleavage-bearing mineral
content and a source of weakness and
leakage problems.

Metamorphic Rocks
• The quartzite which are compact, by virtue of their quartz
content and granulose structure, are neither porous nor
permeable. Therefore, their occurrence at reservoir sites
contribute to water-tightness.
• Marbles, through compact, by virtue of their calcium
carbonate composition and calcite content are not reliable in
terms of their water tightness.
• Slates due to their characteristics slaty due to their
characteristic slaty cleavage may tend to cause leakage but
their very fine grained nature helps in checking such leakage
considerably.

Influence of Geological Structures
• The presence of geological structures has a significant influence
in decreasing and increasing the leakage through rocks, at
reservoir.
• Case 1 shows possibility of occurrence of leakage of reservoir
water into adjacent valley lying at a lower level. The leakage
occurs because the tilted permeable bed is exposed in adjacent
valley.
• Case 2 shows how folding can prevent leakage.
• Case 3 shows how faulting also can prevent leakage. In this
case, along the fault plane, the permeable bed through which
reservior water percolates get terminated against an
impermeable bed which prevents leakage.

Influence of Geological Structures

Influence of Water Table
• WT, depending on its position w.r.t the river level,
either allows the ground water to seep into the river
or vice versa.
• If the water table occurs at a very high level and
intersects the valley sides of the river, then seepage of
GW occurs and gets added to river. Such rivers are
called effluent water.
• If WT occurs at greater depths, the river water
percolates into rock and reaches GW. Such rivers are
called influent waters.

Influence of Water Table
• If river is effluent in nature at reservoir site, no
leakage shall occur, because the ground is already
saturated by GW.
• If the river is of influent nature at reservoir site,
leakage will occur. Any precautions to prevent
leakage will not be satisfactory and downward
percolation is water becomes inevitable under the
influence of gravity.
• Hence only such sites where the rivers are effluent
should be preferred for location of reservoir.

Life of Reservoir
• The process of silting correspondingly reduces the capacity of
the reservoir to store water. The total volume of silt likely to be
deposited in design life of dam is estimated, and that much
volume should be left unused to allow the silting and is known
as dead storage.
• The period up to which the reservoir serves its purpose is life of
reservoir. Life of reservoir increases if the silting is very low
• Measures to control silting are as follows:
Check dams and settling basins
Vegetation
Diversion of sediment loaded water etc.,

GEOPHYSICAL STUDIES
• Geophysical investigations are made for the study of relative
shallow sub-surface inhomogeneties and structure.
• Necessity of Geophysical Investigations:
 To ensure safety, success and economy in construction of major civil
engineering structures, it is necessary to be thoroughly aware of the
geology of the site
• Importance of Geophysical Investigations:
 These can be carried out quickly i.e., large areas can be investigated in a
reasonably short period.
 The instruments are simple, potable and can be operated easily.
 It is economical
 Different inference to suit different purpose can be drawn from the same
field data. Thus, from geophysical investigations information on sub-
surface rock, geological structures, ground water profile, depth of bed

Classification of Geophysical
Methods
• Gravimetric Method
• Magnetic Method
• Electrical Method
• Seismic Method
• Radiometric method
• Geo-thermal methods

• Gravity and magnetic methods can be directly
related to physical properties of rocks, i.e. the
density and the susceptibility, and are very
useful to field geologists and geophysicists in
the mapping and identification of various rock
types.
• They are also used for the detection of
minerals with large contrast in density and
susceptibility compared to country rock.

Gravity Method
• Gravity surveying measures variations in the Earth’s gravitational
field caused by differences in the density of sub-surface rocks.
• Principle:
• In gravity method, the nature of distribution of gravity g, on the
surface is analyzed. The gravity is influenced positively if the rock
is heavier, larger and occurs at shallow depth.
• Gravity methods have been used most extensively in the search for
oil and gas, particularly in the twentieth century.
• Hydrocarbon exploration
• Regional geological studies
• Iso static compensation determination
• Exploration for, and mass estimation of, mineral deposits
• Detection of sub-surface cavities (microgravity)

Magnetic Method
Principle: The magnetic bodies present in the earth’s surface
contribute to magnetic field. When the magnetic field of the
earth is measured on the surface, bodies possessing magnetic
moments different from those of surrounding rocks contribute
to deviations in the measured quantities.
• Application
Detection of rocks
Locating & tracing of faults
Locating iron ores, chromite, manganese and bauxite
deposit.
Detection of geological structures

Magnetic Method
Common uses of magnetometers include:
• Locating buried tanks and drums
• Fault studies
• Mineral exploration
• Geothermal exploration
• Mapping buried utilities, pipelines
• Buried foundations, fire pits for archaeological studies

Electrical Methods
Principle: Electrical properties of the sub-surface formations,
structures, ore deposits are different.
Electrical Resistivity Method: The electrical resistivity of sub-
surface formations vary from one another if they are
inhomogeneous.
Resisitivity rR (ohm-m) is an electrical property. It is the
reciprocal of conductivity
This method evaluate changes in soil types and variations in
pore fluids
This method is used to find depth of bedrock, thickness of
loose overburden, map faults, karts features (caves,
sinkholes), stratigraphy, contaminant plumes.

Electrical Resistivity
Measurements
What will be gained by
changing electrode
spacing?
Depth of ER survey:
i.e., greater spacing
influences deeper

Resistivity Surveys
• Electrical sounding – variations of apparent
resistivity with depth. This study reveals
geology of particular place with increasing
depth.
• Horizontal profiling – lateral variations in
resistivity. This gives information on sub-
surface lithology or structure from place to
place.

Siesmic Method
• Principle: Sub-surface rock formations bear different elastic
properties. Because the velocity of propagation of seismic waves
changes with lithology.
• Seismic techniques are commonly used to determine site geology,
stratigraphy, and rock quality.
• These techniques provide detailed information about subsurface
layering and rock geo mechanical properties using seismic
acoustical waves.
• Reflection and Refraction are the most commonly used seismic
techniques.
• These methods determine geological structure and rock velocities
by either refracting or reflecting waves off boundaries between
rock units with different seismic velocities or impedance.

Theory of the Seismic Method
• There are two types of elastic body wave in a solid:
– P-Waves: compression waves
– S-waves: shear waves
• P-waves are the faster and are usually the ones studied in
simple seismic methods.
• Other waves (surface waves) also exist but are much
slower. It is these waves that do the damage in
earthquakes.
• We will focus our attention on P-waves from now
onward.

Seismic Refraction Methods
• Seismic methods are those that rely on the transmission of
elastic waves through the subsurface.
• These waves are generated by an energy source and are
detected by an array of geophones.
• The raw data consists of the time-series response at each
geophone, which is processed to give the underground
structure.
• The term shallow seismics is used for the detection of
structures at less than ~100m depth. Arrival times are
typically measured in milliseconds (mS).

Refraction Surveys
• Refraction surveys study the critical refracted ray.
• Such a ray can only exist if, at an interface, the lower layer
has a higher impedance than the overlying layer, which
usually implies a higher velocity.
• In practice this is often the case, for example if
unconsolidated sediment overlies bedrock.
• If it is not true, then there is no critical ray and any layer
beneath the interface is hidden. It can then only be revealed
by a reflection survey.

• The critical ray follows the line of the interface and sends
a return ray back to the surface. This is detected by the
geophones.
• The critical ray (or head wave) moves in layer 2 at the
higher velocity. It thus sends a progressive series of
return rays along its path.
• These are detected in turn by each geophone.
• Both the down going and return rays meet the interface at
the critical angle of refraction.
• The time taken to detect these waves will be noted and
based on this reading the thickness of the overburden and
depth of bed rock is found

Seismic Reflection Method
• This method is effective for depths more than
100 mt but are not suitable for shallow
exploration
• They are capable of identifying anticlines,
synclines, domes and faults etc.,

Radiometric method:
• The radiometric method is a geophysical process used to estimate
concentrations of the radio elements potassium, uranium and
thorium by measuring the gamma-rays which the radioactive
isotopes of these elements emit during radioactive decay.
• Airborne gamma-ray spectrometric surveys estimate the
concentrations of the radio elements at the Earth's surface by
measuring the gamma radiation above the ground from low-flying
aircraft or helicopters.

Application of Radiometric
Methods
• Exploration of Uranium and thorium mineral deposits
• Geological mapping: location of faults, shear zones
etc., can be done by radiometric methods
• To find leakages in water storage and conveyance
systems.
• Detection of ground water table & presence of salt
water intrusions
• Exploration of oil & gases.

Geothermal Method
• The heat conductivity character of sub-surface rock depends on
rock formations, their structures and ore bodies.
• The applications are as follows:
Structural study of that day
Ground water studies
Delineation of salt water and fresh water.

GROUTING:
• Grout is a particularly fluid form of concrete used to fill gaps. It
is used in construction to embed rebar's in masonry walls,
connect sections of pre-cast concrete, fill voids, and seal joints
such as those between tiles.
• Grout is generally a mixture of water, cement, sand, often color
tint, and sometimes fine gravel (if it is being used to fill large
spaces such as the cores of concrete blocks).
• Finer particle sizes let the grout penetrate more deeply into a
fissure.

IMPROVEMENT OF COMPTENCE OF SITE
GROUTING
 Even hard rocks are unsuitable for dam foundation if the
geological structures like faulting, jointing are present.
 The method of grouting involves the forceful injection of slurry
of water and cement into the fractured rock of the site.
 The spacing of grouting holes depends on extent of weakness of
ground and degree of compactness required.
 Grouting reduces percolation by filling the fissures of the site
rocks.
 To improve the strength sodium silicate and calcium chloride
are mixed with the slurry.
 During grouting, sodium silicate solution is first pumped into
the ground and when the openings of the rock are filled with
this solution, a calcium chloride is introduced.

IMPROVEMENT OF COMPTENCE
OF SITE GROUTING
• The chemical reaction takes place within the rock
mass and a permanent gel is formed which imparts
strength of site rock.
• Advantages of grouting
 It can be taken up anywhere, irrespective of
composition of rock.
The gel used is inert and will not attack either
concrete or steel.

PERMEATION GROUTING:
• Permeation Grouting consists of injecting grout under
controlled, low pressure in order to permeate the strata without
causing fracturing.
• It can be applied in both soil and rock.

Geology of Dams & Reservoirs

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