project on dam and dam safety with application of geophysics
DD HOOVER DAM is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the
border between the US states of AMERICA.
DAM AND DAM SAFETY
EARTH SCIENCE PROJECT
RIPU DAMAN SINGH , 12215008,
DAM AND DAM SAFETY
Dam is a solid barrier constructed at a suitable location across a river valley to store
REVIEW OF LITERATURE
First dam was constructed by the Egyptians in 2950-2750 B.C, using stone/ brick ma-
Earth dam was built first in Mesopotamia around 2000 B.C.
Romans used concrete and mortars around 100 AD.
Due to large size and amount of building material need to construct earth and gravity
Grand Anicut (Kallanai)
The oldest dam in the world
Built by Chola king Karikalan around the 2nd Century AD
To divert the waters of the Kaveri across the fertile delta region for irrigation via canals.
It is constructed from unhand stone spanning the Kaveri and is 329 m (1,079 ft.) long,
20 m (66 ft.) wide and 5.4 m (18 ft.) high
Water for domestic consumption
Drought and flood control
For navigational facilities
Hydroelectric power generation
Development of fish & wild life
The following factors shall be considered when selecting the site of a dam.
Topography: the dam should be located where the river .Has a narrow gorge which opens
out upstream to create a large reservoir. The dam should be preferably located where the
river bed is high, to reduce the height and cost of the dam.
Suitable Foundation: Suitable foundation should exist at the site for the particular type of
dam. For gravity dams of great height, sound rock is essential.
Good Site for reservoir: site should have the following characteristics to make a good site
for a reservoir:
(i) Large storage capacity: The topography of the site should be such that the reservoir has a
large capacity to store water.
(ii) Shape of reservoir basin: The reservoir basin on the upstream of the dam should preferably be
cup-shaped, with a flat bottom but steep slopes.
(iii) Watertightness of the reservoir: The geological conditions of
the reservoir site should be such that the reservoir basin is watertight. The reservoir sites
having pervious rocks are not suitable. The reservoir basins having shales, slates, schists,
gneiss, granite, etc. are generally suitable.
(iv) Good hydrological conditions: The hydrological conditions of the river at the reservoir site
should be such that adequate runoff is available for storage. The catchment area of the river
should give high yield. There should not be heavy losses in the catchment due to evaporation,
transpiration and percolation.
(v)Deep reservoir: The site should be such that a deep reservoir is formed after the construction
of the dam. A deep reservoir is preferred to a shallow reservoir because in the former the
evaporation losses are small, the cost of land acquisition is low and the weed growth is less.
(vi) Small submerged area: The site should be such that the submerged area is a minimum. It
should not submerge costly land and property. It should not affect the ecology of the region.
Monuments of historical and architectural importance should not be submerged.
(vii) Low siltin flow: The dam site should be such that the reservoir would not silt up quickly. The
life of the reservoir depends upon the rate of silting. The site should be selected such
that it avoids or excludes the water from those tributaries which carry a high percentage of
silt, i.e. if any tributary carries relatively large quantity of sediments, the dam should
be constructed upstream of the confluence of that tributary with the river.
(viii) No objectionable minerals: The soil and rock mass at the reservoir site should not contain
any objectionable soluble minerals which may contaminate the water. The stored water should be
suitable for the purpose for which the water is required.
Earthquake hazards: If the dam site is located in a seismic zone, the most
suitable type of the dam is one which can resist the earthquake shock without much
damage. Earth dams and rock fill dams are generally more suitable for such sites,
provided suitable modifications are made in the design. However, by adopting
suitable measures and considering various forces and factors affecting the seismic
design, other types of dams can also be provided.
Climatic conditions: Climatic conditions should also be considered while
selecting the type of dam. In extremely cold climates, buttress and arch dams should
be avoided. These dams have thin concrete sections and are easily damaged due to
spilling of concrete which occurs due to alternate freezing and thawing. Similarly, if
there are frequent rains and the climate is extremely wet, it will be difficult to
control water content of the soil and compaction in an earth dam. Therefore, earth
dams should be avoided.
Environmental considerations: The dam and its appurtenant works should
be aesthetically acceptable and they should not have any adverse effect on ecology
and environment. Generally, earth dams are more suitable than concrete dams for
aesthetical consideration. They merge easily with the natural environment in the
INVESTIGATION FOR DAM
The following investigations are usually conducted locate the most suitable site for a dam
1. Engineering surveys: Engineering surveys are conducted for the dam, the reservoir
and other associated works. Generally, the topographic survey of the area is carried out and
the contour plan is prepared. The horizontal control is usually provided by triangulation
survey and the vertical control by precise levelling. For the area in the vicinity of the dam
site, a very accurate triangulation survey is conducted. A contour plan to a scale of 1/250 or
1/500 is usually prepared. The contour interval is usually 1 m or 2 m. The contour plan
should cover an area at least upto 200 m upstream and 400 m downstream and for adequate
width beyond the two abutments. For the reservoir, the scale of the contour plan is usually
1/15,000 with a contour interval of 2 m to 3 m, depending upon the size of the reservoir. The
area-elevation and storage-elevation curves are prepared for different elevations upto an
elevation 3 to 5 m higher than the anticipated maximum water level (MWL).
2. Geological Investigations: Geological Investigations of the dam and reservoir site
are done for (a) Suitability of foundation for the dam, (b) Watertightness of the reservoir basin,
and (c) Location of the quarry sites for the construction materials. Subsurface explorations
are carried out to determine the depth of overburden to be removed for laying the foundation
of the dam, the type of rock, the nature and extent of the fault zones, if any, present in the
rock. The information obtained from the geological investigations is used for devising a
suitable programme of foundation treatment and grouting if necessary. Geological
investigations are conducted to detect the presence of faults, fissures, and cavernous rock
formations which have cavities and are porous. If such formations exist in small areas, they
may be treated and made watertight. However if they are wide spread, the site may have to be
abandoned. Geological investigations are also conducted for location of suitable quarries for
stones and borrow areas for soils. The quality and the quantity of the available construction
materials are also ascertained.
3. Hydrological Investigations:
Hydrological Investigations are conducted
(a) to study the runoff pattern and to estimate yield and
(b) to determine the maximum discharge at the site.
The most important aspect of the reservoir planning is to estimate the quantity of water
likely to be available in the river from year to year and seasons to season. For the
determination of the storage capacity of a reservoir, the runoff pattern of the river at the dam
site is required. The spillway capacity of the dam is determined from the inflow hydrograph
for the worst flood when the discharge in the river is the maximum. Flood routing is done to
estimate the maximum outflow and the maximum water level reached during the worst flood.
The methods for the fixation of reservoir capacity, for the estimation of the maximum flood
discharge, and for flood routing are already learnt in Hydrology course.
4. Sub-surface exploration: Sub-surface exploration programme usually
includes one or more of the following methods.
(i) Geophysical method,
(ii) Sounding and penetration methods,
(iii) Open excavations,
(iv) Exploratory boring,
(v) Rock drilling.
Foundations of a dam are usually of the following two types:
(a) Rock foundation, and
(b) Alluvial foundation.
High dams are usually constructed on rock foundations. Moreover, the spillways and outlets are
normally built on sound rock. Thorough subsurface explorations of rocks are carried out to de-
termine the depth of overburden, location of fault zones, extent of jointing, existence of
solution cavities, presence of soluble materials, disintegration of rock, etc. The
presence and nature of clay or any other material in the seams of the jointed or
fractured zones of the rock should be specially investigated. Such materials create
problems and may even lead to failure when the reservoir is filled and very high
hydrostatic pressure develops. The depth of exploratory investigations should be
taken upto the bed rock. If the bed rock is at great depth, there should be at least one
boring upto the bed rock. Investigations must be done through all soft, unstable and
permeable strata of the overburden. For large dams, the foundations should be
thoroughly investigated to great depths. Alluvial foundations consist of sand, gravel,
silt and clay. Generally, earth dams and low gravity dams are constructed on such
foundations. For all other types of dams, rock foundations are required. Geophysical
methods and sub-surface soundings are used to determine the depth of bed rock. The
properties of soils such as permeability, density, consolidations characteristics and
shear strength are determined.
1. Seismic Refraction Surveys.- Seismic refraction
surveys are performed to determine the compressional-
wave velocities of materials from the
ground surface down to a specified depth. the objective of a seismic refraction
survey is to determine the configuration of the bedrock
surface and the compressional-wave velocities
in the surficial deposits. Bedrock may be defined in
terms of compressional-wave velocity.
Applications.-Seismic refraction surveys
have been used in many types of exploration programs
and geotechnical investigations. Seismic refraction
surveys are routinely used in foundation
studies for construction projects and in siting studies,
fault investigations, dam safety analyses, tunnel
alignment studies, and rippability studies.
Equipment.-The basic equipment used for
seismic refraction work consists of a seismic amplifier,
a recorder (oscillograph or an oscilloscope)
and a transducer (geophone). Depending on the
scope of work, a single channel (one geophone) to
a multichannel system may be required.
2. Seismic Reflection Survey –P Seismic reflection
surveys provide information on the geological
structure within the earth. The information obtained from
seismic reflection surveys can be used to define the
geometry of subsurface layers and, thereby, provide
information on faulting.
Applications-High-resolution seismic reflection
surveys have been used in a large number
of engineering investigations to provide definitive
information on the locations and types of faults and
the locations of buried channels.
In some cases where it is not practical to use seismic
refraction reflection surveys is very similar to that
used for seismic refraction surveys. In some cases,
the equipment may be identical. For civil engineering
investigations and ground-water studies, small
portable equipment of up to 24 channels may
3. Shear- Wave Surveys.-Shear waves travel
through a medium at a slower velocity than compressional
waves. Therefore, shear-wave arrivals
occur after compressional-wave arrivals on seismograms,
or they are recorded as secondary arrivals.
Application.-In engineering investigations
shear-wave velocities are important because they
can provide information on the inplace dynamic
properties of a material. The relationship between
compressional-wave velocity, shear-wave velocity,
unit weight, and the inplace dynamic properties of
a material is shown on figure 534.
4. Surface Waves.-Surface-wave surveys are
designed to produce and record surface waves and
their characteristics. Surface waves, which travel
along the boundaries between different materials,
are the slowest seismic waves. Because there are
different types of surface waves, not only must the
waves be recorded, but their characteristics must
also be determined.
Applications. -The principal application of
shear-wave surveying, for geotechnical investigations,
is to determine the type and characteristics
of surface waves that can exist at a given site. This
information is useful for determining preferred site
frequencies; and for earthquake design analysis.
Equipment.-The cables and amplifiers used
in normal refraction surveying can also be used in
5. Vibration Surveys.-Vibration surveys
measure the vibrational levels produced by mechanical
or explosive sources. Once these levels are
determined, procedures can be designed to reduce
the possibility of vibrational damages.
Applications. - Vibrational surveys have
been performed in conjunction with quarrying and
mining operations, during excavations, to measure
the effects of traffic on sensitive equipment, and to
measure the effects of aircraft (sonic vibrations) on
urban areas and on historic buildings.
Equipments-Many manufacturing and research facilities
Use geophones are three-component, low frequency
geophones, similar to (or the same as) those used in surface wave
surveys. Most equipment can record ground
motion in terms of particle displacement, velocity,
or acceleration. Some equipment only records on
6. Electrical-Resistivity Profiling Surveys.-
Electrical-resistivity profiling is based on the measurement
of lateral changes in the electrical properties
of subsurface materials. The electrical
resistivity of any material depends
is used to detect lateral changes in the electrical
properties of subsurface material, usually to a specified
depth. This technique has been used to map
the lateral extent of sand and gravel deposits, to
provide information for cathodic protection of underground
utilities, to map the lateral extent of contamination
plumes (in toxic waste studies), and in
fault exploration studies.
Equipment.-Most electrical-resistivity surveying
equipment consists of a current transmitter, a receiver (to measure the resulting poten-
tial), two (or more) current electrodes and two (or more) potential
7. Electrical-Resistivity Soundings.-Electrical-
resistivity sounding is based on the measurement
of vertical changes in the electrical properties
of subsurfe.ce materials. In contrast to resistivity
profiling, in which the electrode separation is fixed,
the electrode spacing used for resistivity sounding
is variable, while the center point of the electrode
array remains constant. The depth of investigation
increases in a general sense as the electrode spacing
increases, thus resistivity soundings are used to investigate
variations of resistivity with depth.
often referred to as VES (vertical electrical
soundings), are commonly used for aquifer and
aquaclude delineation in ground-water investigations.
They have been used for bedrock delineation
studies, where there may not be enough contrast in
velocity to permit seismic surveying.
Equipment.-The equipment used in resistivity
sounding is identical to the equipment used
in electrical-resistivity profiling. For shallow investigations
a d-c (direct current) transmitter is normally
sufficient; whereas, for deeper investigations
an a-c (alternating current) transmitter may be
8. Electromagnetic-Conductivity Sounding Surveys.-
The basic principles involved in EM surveying
have been discussed in the previous paragraphs.
Electromagnetic sounding surveys are used to determine
vertical changes in the conductivity of surface
surveys have been applied to delineate areas of
permafrost, to locate gravel deposits, to map bedrock
topography, and to provide general geologic
information. The EM sounding and profiling surveys
have also been applied to fault studies.
Equipment.-The equipment used in EM
sounding surveys is the same as that used in EM
profiling surveys. For shallow investigations, less
sophisticated equipment is required than for deeper
9. Ground-Probing Radar.-Ground-
radar surveys have the same general characteristics
as seismic surveys. However, the depth of investigation
with radar is much more shallow bhang that
of a seismic survey. This disadvantage is partially
offset, however, by the much greater size-resolution
of radar techniques.
Applications-Ground-probing radar surveys
can be used for a variety of very shallow engineering
applications, including locating pipes or
other buried objects, high-resolution mapping of
near-surface geology, locating near-surface cavities,
and locating and determining the extent of piping
caused by sink-hole activity and leakage in dams.
These applications are limited, however, by the
very small depth of penetration usually possible
with the very high frequencies involved in radar.
Silts, clays, salts, saline water, the water table, and
any other conductive materials in the subsurface
will severely restrict or even prevent any further
penetration of the subsurface by the radar pulses.
Equipment.-The equipment for ground probing
radar is manufactured by only two or three
companies at this time, and only a few contractors
offer these services. Therefore, the present sources
for equipment and-contract services are limited.
The equipment itself consists of an antenna/receiver
sled, a control/signal processor unit, a strip chart
recorder, a power supply, and various accessories,
such as a tape recorder and special signal
analyzers. This equipment would normally he operated
from a vehicle, except for the antenna/receiver
sled, which can be either towed behind the
vehicle or pulled by hand. A schematic diagram of
radar operations is shown on figure 5-37.
Dams are constructed to impound water for storage or to divert water for beneficial use.
Unfortunately, the impoundment of water sometimes poses a potential hazard to public
safety. The purpose of a dam safety program is to recognize potential hazards and re-
duce them to acceptable levels.
Seismic refraction and MASW
Seismic refraction Is a use full method for investigation geological structure and rock
properties. The technique Involves the
Observation of a Seismic signal That has Been refracted between layers of contrasting
seismic veloci ty.
The geophysical survey use non-destructive method to allow extensive investgations of various
hydro technical projects
--‐ Land, rock or concrete dams
--‐ Protection dykes
--‐ Functional dykes
Geoelectrical- Using the Vertical Electrical Survey (SEV), Electrical Tomography This method Has proven
Most efficient For locating Areas of Water infiltrations And for Scanning the density Of the built in Material from The
dykes Or dams.
Georadar (GPR)-It has a very high resolution and accuracy for areas made of concrete ,locating holes and
anomalies in the density of the material below.
Seismical -This Profiling method can accurately show data ab out the homogeneity of the built in ma-
terial from dams or dykes.
RESULTS AND DISCUSSIONS
Dams in the country represent a major investment and huge benefits to population in
terms of irrigation, power and flood control. Most of the big dams are very old and regu-
lar monitoring and maintenance of these dams is of utmost importance for continuing
benefits. Unlike soil investigations, critical nature of dams, does not permit traditional
invasive inspections by means of drilling, and such inspections are best avoided unless
extremely important, and are done only when problem is too grave.
Geophysical techniques, by virtue of their non-invasive and non-destructive nature, offer
an excellent solution for investigation or regular monitoring of dams, and detection of
anomalous conditions which might snowball into major problems if left untreated.
Various geophysical methods are available to investigate the problems of earthen, ma-
sonry, concrete or composite dams:
Seismic reflection and refraction surveys
Shear and surface wave surveys
Electrical resistivity and profiling surveys
Ground probing radar
A number of geophysical techniques are utilised to evaluate conditions at existing dam sites.
Most of these methods find application on earth or rockfill structures with some methods also
effective on concrete dams. The main applications of geophysical methods at existing dams are
related to seepage assessment, integrity evaluations, foundation conditions and seismic hazard
estimation. Anomalous seepage is most readily identified with the self or streaming-potential
For geophysical method
Griffiths, D. H., and R. F. King, Applied Geophysics for
Engineers and Geologists, Pergamon Press, New York, NY,
Heiland, C. A., Geophysical Exploration, Hafner, New
York, NY, 1968.
For dam safety
Committee on the Safety of Existing Dams, Water Science
and Technology Board, Commission on Engineering
and Technical Systems, National Research Council, National
Academy Press, Washington, D.C., 1983.
“Criteria for Selecting and Accommodating Inflow Design
Floods for Storage Dams and Guidelines for Applying
Criteria to Existing Storage Dams,” ACER Technical
Memorandum No. 1, Bureau of Reclamation, Denver,
CO, November 1981.