Ground Water (Unit-V) Engg Geology

1. Ground Water
Unit-V Part-I

2. Ground Water
Ground water
• Sources and zones, water table, unconfined and perched,
springs, Factors controlling water bearing capacity of rocks,
pervious and impervious rocks, cone of depression and its
use in civil engineering, Methods of artificial recharge of
ground water, geology of percolation tank.
Geophysical Investigation
Necessity, Methods of surface and sub surface
investigations, Importance of Electrical Resistivity Method,
Seismic Refraction Method, Preliminary geological
investigations, Use of aerial photographs and satellite
imageries in civil engineering projects

3. Ground Water
• The ground water is considered a very
important natural resource, in arid , semi arid
and dry regions, this may be the only source of
water supply. Even in humid
areas, groundwater is considered a better
resource for many economic and hygienic
reasons.

4. Ground Water

5. Ground Water
Ground Water
• Has a suitable composition in most cases and is free
from turbidity, objectionable colors, and pathogenic
organisms and require not much treatment.
• Is relatively much safer from hazards of chemical,
radiogenic and biological pollution to which surface
water bodies are exposed
• Supplies are not quickly affected by drought and other
climatic changes and hence are more dependable.
• Being available locally in many cases may be tapped and
distributed at much lesser cost using very little network
of pipes

6. Ground Water

7. Ground Water
Sources of groundwater
Meteoric Water
• It is the water derived from precipitation (rain and snow)
although bulk of the rain water or melt water from snow
and ice reaches the sea through the surface flows or
runoffs a considerable part of precipitation gradually
infiltrates into ground water. This infiltrated water
continuous its downward journey till it reaches the zone
of saturation to become the ground water in the aquifer.
• Almost entire water obtained from ground water
supplies belongs to this category.

8. Meteoric Water

9. Ground Water
Connote Water
• This is the water present in the rocks right from the time
of their deposition in an aqueous environment. During
the process of formation of sedimentary rock in a lake or
sea or river, depositions is followed by compaction,
which leads to the squeezing out of most of the water
present between the sediments. Sometimes however,
incomplete compaction may cause retention of some
water by these rocks which is known as connote water.
And it may be found in rocks like limestone, sandstone
and gravels. It is saline in nature and is of no
importance as a source for exploitable groundwater.

10. Ground Water

11. Ground Water
Juvenile Water
• It is also called magmatic water and is of only
theoretical importance as far as water supply
scheme is concerned. It is the water found in
the cracks or crevices or porous of rocks due to
condensation of steam emanating from hot
molten masses or magmas existing below the
surface of the earth. Some hot springs and
geysers are clearly derived from juvenile water.

12. Ground Water
Distribution of Ground Water
• The water that goes below the surface of the
land may be found to exist in two main zones
or environments classified as Vadosa Water
and phreatic water or groundwater
• In the vadosa water zone itself, three different
types of environment are distinguished; soil
water, intermediate vadose water and capillary
water.

13. Ground Water
• The soil water forms a thin layer confined to the near surface depth
of the land. It may occur at depth between 1.0 to 9 m and is held up
by the root zone of vegetable cover of the globe It is lost to the
atmosphere by transpiration and evaporation.
• The intermediate vadosa zone occurs immediately below the zone of
soil water. It is in fact a zone of non saturation; water in this zone is
moving downward under the influence of gravity. It is generally of
smaller thickness and may be even absent in many cases. The above
zones are sometimes collectively referred as zone of aeration.
• The zone of capillary water, also called as capillary fringe. Is present
only in soil and rocks of fine particles size underlying the vadosa
zone. In the fine particle size zone, groundwater is drawn upward by
capillary action, sometimes to height of 2-3 m above saturated zone
lying underneath. Growth of vegetation in some desert is very often
dependent on presence of capillary fringe.

14. Ground Water

15. Ground Water

16. Ground Water

17. Distribution of Ground Water

18. Ground Water
The Phreatic Water Zone
• Also known as zone of saturation lies below the capillary
fringe and is the water held in this zone that is called
groundwater in the real sense. The upper surface of water in
the zone marks the water table in the area. In this zone the
layers or bodies of rocks which are porous and permeable,
have all their open spaces such as pores, cavities, cracks etc.
completely filled with water. All these openings are
interconnected, so that a well dug into this openings are
completely filled with water, there is no or very little
downward movement of groundwater. In all ground water
exploration programmes, the main objective is to locate this
zone and determine its extent, geometry and character.

19. Ground Water

20. Ground Water

21. Ground Water
Forms of Subsurface Water
• Water in the soil mantle is called subsurface
water and is considered in two zones
• Saturated Zone
• Aeration Zone.

22. Water table generally
below surface, so water
can seep in
Water can soak into
subsurface and become
groundwater
Where water table intersects
surface, water can flow out

23. Ground Water

24. Ground Water
Saturated Zone
• This Zone is also known as groundwater zone in which
all the pores of the soil are filled with water. The water
table forms the upper limit and marks a free
surface, i.e. a surface having atmospheric pressure.

25. Ground Water
Zone of Aeration
• In this zone the soil pores are only partially saturated
with water. The spaces between the land surface and
the water table marks the extent of this zone. The zone
of aeration has three subzones.

26. Ground Water

27. Ground Water
Soil water zone
• This lies close to the ground surface in the major band of the
vegetation from which the water is lost to the atmosphere by
evapotranspiration.
Capillary Fringe
• In this the water is held by the capillary action. This zone extends
from water table upwards to the limit of the capillary rise.
Intermediate Zone
• This lies between the soil water zone and the capillary fringe. The soil
texture and moisture content and vary from region to region. The soil
moisture in the zone of aeration is of importance in agricultural
practices and irrigation engineering.

28. Ground Water

29. Ground Water
Saturated Formations
• All earth materials from soils to rocks have pore spaces.
Although these pores are completely saturated with water table
below, from the groundwater utilization aspect only such
material through which water moves easily and hence can be
extracted with ease are significant. On this basis the saturated
formation are classified into four categories.
• Aquifer
• Aqitard
• Aquiclude
• Aquifuge

30. Ground Water
Aquifer
• An aquifer is a saturated formation of earth
material which not only stores water but yields it
in sufficient quantity. Thus an aquifer transmits
water relatively easily due to high permeability.
Unconsolidation deposits off sand and gravel
form good aquifer.

31. Ground Water

32. Ground Water
Aquitard
• It is a formation through which only seepage is
possible and thus the yield is insignificant compared to
an aquifer. It is partly permeable. A sandy clay unit is
an example of aquitard. Through an aquitard
appreciable quantities of water may leak to an aquifer
below it.

33. Ground Water

34. Ground Water
Aqiclude
It is a geological formation which is
essentially impermeable to the flow of water. It
may be considered as close to water movement
even though it may contain large amount of
water due to its high porosity. Clay is an
example of an acquiclude.

35. Ground Water

36. Ground Water
Aquifuge
• It is a geological formation which neither
porous nor permeable. There are no
interconnected openings and hence it cannot
transmit water. Massive compact rock without
any fracture is an acquifuge.

37. Ground Water
Aquifer
• Formation of ground which contain water and
may transmit water in usable quantity are
known as aquifer. Thus these are the geological
formations in which groundwater occurs. (i.e.
Sands, gravels).

38. Confined aquifer
overlain by less
permeable
materials
Unconfined aquifer
open to Earth’s surface
and to infiltration
Perched aquifer underlain by
low-permeability unit
Artesian aquifer: water rises in
pipe (maybe to surface)

39. Ground Water
Aquifer are mainly of two types
Unconfined Aquifer
• An unconfined aquifer is the one in which water table forms the
upper surface of the zone of saturation. An aquifer where the
water table is the upper surface limit and extends below till the
impermeable rock strata is called the unconfined aquifer.
Confined Aquifer
• When an aquifer is sandwiched between two impermeable
layers, it is known as a confined aquifer. It is also known as a
pressure aquifer, or an artesian aquifer. Confined aquifers are
completely filled with water and they do not have a free water
table and the aquifer will be under pressure.

40. Ground Water

41. Ground Water
Leaky Aquifer
• An aquifer bound by one or two aquitards is
known as a leaky aquifer. It is also known as semi-
confined aquifer.
Perched Aquifer
Perched Aquifer is a special type of an unconfined
aquifer. An impermeable saucer-shaped stratum of
a small aerial extent occurring in the zone of
aeration may retain and hold some amount of
water is called perched aquifer.

42. Ground Water

43. Ground Water

44. Ground Water
Water Table
A water table is the free water surface in an
unconfined aquifer indicating the level of the
water table at that point. The water table is
constantly in motion adjusting its surface to
achieve a balance between the recharge and
outflow from the surface storage.

45. Ground Water

46. Water Table
• Fluctuations in the water level in a dug well during
various seasons of the year, lowering of the
groundwater table in a region due to heavy
pumping of the wells and the rise in the water table
of an irrigated area with poor drainage, are some
common examples of the fluctuation of the water
table. In a general sense, the water table follows the
topographic features of the surface. If the water
table intersects the land surface the ground water
comes out to the surface in the form of springs or
seepage.

47. Ground Water

48. Aquifer Character of Commonly Occurring
Rocks
Igneous Rocks
• Among different igneous rocks we know that there are
three subdivisions: Plutonic, hyperbassal and
volcanic, granites, dolerite and basalts are the most
abundant among these subdivisions, respectively. Of
these.
• Granite and dolerites have not only an interlocking
texture but also being intrusive, they are massive, dense
and compact. As a result they have negligible porosity
and permeability.
• So these rocks are typical examples of aquifuges. They
can bear ground water only when they are either
intensely fractured or have undergone considerable
weathering.

49. Aquifer Character of Commonly
Occurring Rocks
• However, as both weathering and fracturing
decreases with depth and disappears, no ground
water can be expected in such rock at great depth.
Volcanic rocks are often vesicular, In these vesicles
are of considerable size and number and if these
are interconnected they can serve as aquifer.
• The contraction joints and other fractures, if
present, also contribute to the porosity and
permeability character of igneous rocks.

50. Igneous Rocks

51. Aquifer Character of Commonly Occurring
Rocks
Sedimentary Rocks
• Among Sedimentary Rocks, the most common ones are
shales, sandstones ad limestones. Of these sandstones and
shales are formed out of the deposition of mechanically
transported sediment.
• A generalization may be made that coarse, rounded, sorted, less
compacted and poorly cemented rocks are more porous. In
this case of dense and fine grained limestone, they have no
primary porosity, but solution cavities and channels are
common in them which sometimes make these rocks highly
porous.
• All the forgoing rocks may also have joints, faults, shear
zones, cracks etc. which contribute to additional porosity in
them.

52. Sedimentary Rocks

53. Aquifer Character of Commonly
Occurring Rocks
• In sediments and sedimentary rock the following
represent the increasing order of aquifer character:
clays, shale, limestone, sandstones, sandstones, san
d and gravel.
• Shales are impermeable rocks, though considered
porous. Clay may have 50- 60 % porosity. But
when wet, they may become plastic and close the
fractures. Sandstones, though less porous than
shales are fairly permeable rocks. Thus but virtue
of reasonable porosity and permeability, these
make up common and good aquifer.

54. Aquifer Character of Commonly Occurring
Rocks
Metamorphic Rocks
• Foliations and/or lineation, if present and well
developed, may contribute some porosity to
metamorphic rocks. But as such rocks are formed under
great pressure. Primary porosity cannot be expected to
be much. Among the foliated group of metamorphic
rocks, gneisses are less porous than schist's.
• Among the non-foliated rocks, quartzite have very little
porosity by virtue of their compactness and granulose
texture. Hence they are unsuitable for ground water
occurrence.

55. Metamorphic Rocks

56. Cone of Depression or Cone of
Exhaustion
• In any gravity well (i.e. well dug in an unconfined aquifer),
the static level of water coincides with the water table level of
the surrounding aquifer. When water is pumped out in a
considerable measure from the well, the level of water in it
goes down leading to the depression in the water table
around the well in the form of inverted cone. This
phenomenon is called cone of depression or the cone of
exhaustion This is a temporary fluctuations in the level of
water table because the original position is restored within a
short period due to the seepage of ground water from the
sides of the well (i.e. aquifer). The shape of this cone of
depression on the water table around a pumped well
depends on the permeability nature of aquifer body.

57. Cone of Depression or Cone of
Exhaustion

58. Cone of Depression or Cone of
Exhaustion
• In case of highly permeable material, the cone
of depression is nearly flat, while in less
permeable aquifers, it is very steep. The
boundaries of the cone of depression is known
as the ground water divide. The area enclosed
by the ground water divide is termed as the area
of pumping depression. The distance between
the well and the ground water divide is termed
as the radius of influence.

59. Cone of Depression or Cone of
Exhaustion

60. Artificial Recharge Techniques
The artificial recharge techniques can be broadly categorized as
follows:-
a. Direct surface techniques
• Flooding
• Basins or percolation tanks
• Ditch and furrow system
b. Direct sub surface techniques
• Injection wells or recharge wells
• Recharge pits and shafts
• Dug well recharge
• Bore hole flooding
• Natural openings, cavity fillings.

61. Artificial Recharge Techniques
c. Combination surface
• Sub-surface techniques
• Basin or percolation tanks with pit shaft or wells.
d. Indirect Techniques
• Induced recharge from surface water source.
• Aquifer modification.

62. Ditch and Furrow Method
Ditch and Furrow Method
• In areas with irregular topography, shallow, flat
bottomed and closely spaced ditches or furrows
provide maximum water contact area for recharge
water from source stream or canal. This technique
requires less soil preparation than the recharge
basins and is less sensitive to silting. Shows a
typical plan or series of ditches originating from a
supply ditch and trending down the topographic
slope towards the stream.

63. Ditch and Furrow Method

64. Percolation Tanks (PT) / Spreading Basin
Percolation Tanks (PT) / Spreading Basin
• These are the most prevalent structures in India as a
measure to recharge the ground water reservoir
both in alluvial as well as hard rock formations.
• The efficacy and feasibility of these structures is
more in hard rock formation where the rocks are
highly fractured and weathered. In the States of
Maharashtra, Andhra Pradesh, Madhya
Pradesh, Karnataka and Gujarat, the percolation
tanks have been constructed in plenty in basaltic
lava flows and crystalline rocks.

65. Percolation Tanks (PT) / Spreading
Basin
• These are found to be very effective in Satpura
Mountain front area in Maharashtra.

66. Percolation Tanks (PT) / Spreading
Basin

67. Important Aspects of Percolation
Tanks
• Percolation tanks be normally constructed on second to
third order stream since the catchment so also the
submergence area would be smaller.
• The submergence area should be in uncultivable land as
far as possible.
• Percolation tank be located on highly fractured and
weathered rock for speedy recharge. In case of
alluvium, the boundary formations are ideal for locating
Percolation Tanks.
• The aquifer to be recharge should have sufficient
thickness of permeable vadose zone to accommodate
recharge.

68. Important Aspects of Percolation
Tanks
• The benefitted area should have sufficient number
of wells and cultivable land to develop the
recharge water.
• Detailed hydrological studies for run off
assessment be done and design capacity should
not normally be more than 50% of total quantum
of rainfall in catchment.
• Waste weir or spillway be suitably designed to
allow flow of surplus water based on single day
maximum rainfall after the rank is filled to its
maximum capacity.

69. Important Aspects of Percolation
Tanks
• Cut off trench be provided to minimize
seepage losses both below and above nalla bed.
• To avoid erosion of embankment due to ripple
action stone pitching be provided upstream
upto HFL.
• Monitoring mechanism in benefitted as well as
catchment area using observation well and staff
gauges be provided to assess the impact and
benefits of percolation tank

70. Geophysical Investigations
• Geophysical investigations involve simple methods of
study made on the surface with the aim of ascertaining
subsurface detail. This is achieved by measuring
certain physical properties and interpreting them
mainly in terms of subsurface geology.

71. Importance of Geophysical
Investigations
• Geophysical methods are gaining importance very
rapidly because of their success in solving a vast
variety of problems.
• These investigations are carried out quickly. This
means large area can be investigated in a
reasonable short period and hence time is saved.
• The geophysical instruments used in the field are
simple, portable and can be operated easily. This
means fieldwork is not laborious.
• Since the work is carried out quickly and only
physical observations are made. Without the use of
consumables (like Chemicals), it is economical too.

72. Importance of Geophysical
Investigations

73. Importance of Geophysical
Investigations
• Different interferences to suit different
purposes can be drawn from the same field
data, for example electric resistivity data can be
interpreted for knowing subsurface of rock
types, geological structures, groundwater
conditions, ore deposits depth to the bed rock,
etc. Hence the investigations are multipurpose.

74. Applications of Geophysical
Investigations
• Geophysical explorations are numerous, important
and widely varied.
• Investigations aimed in solving problems of
regional geology.
• Investigations aimed at locating and estimating
economically important mineral deposits.
• Investigations aimed at locating and assessing
groundwater potential and its quality
• Investigations aimed at solving problems
connected with geology.

75. Classification of Geophysical Methods
• There are many kinds of geophysical methods of
investigation. These method are
• Gravimetric method
• Magnetic method
• Electrical method
• Seismic method
• Radiometric method
• Geothermal method

76. Gravity Methods
• Gravity method represent a set of geophysical methods which
make use of the natural gravity field of the earth.
• Physical Property
• Density of the material is the controlling physical property.
• Principle
• In gravimetric method, the nature of distribution of gravity g
on the surface is analyzed. The gravity is influenced positively
if the causative body is heavier, larger and occurs at a shallow
depth.
• The gravimeter, used in relative gravity measurement is a
mass loaded spring. If the subsurface has a relatively heavier
body, the gravity pull is more there (+g) and the spring
extends becoming longer. If the subsurface has relatively a
lighter body there the gravity pull is less (-g) and the spring
contracts and become shorter.

77. Gravity Methods

78. Gravity Methods

79. Gravity Methods
1 Gal is precisely equal to 0.01 m/s2.

81. Gravity Methods
• Thus in a particular region, if surface bodies
such as (ore deposits, coal seams and salt
domes) whose densities are different from the
surrounding rocks exist, the gravity field
deviates from the normal value then expected
from this deviations it is possible to locate the
inhomogeneous bodies in the surface.

82. Gravity Investigations
• Gravity investigations are useful in
• Exploration of ore deposits
• In solving regional geological problem
• In exploration of oil and natural gas deposits
• In solving some engineering problems
• Gravity investigations are carried out always during oil
and gas investigations because of their special success in
that area.
• In case of engineering problems, mapping of dam sites,
earthquake problems, tracing buried river channels
gravity method are considerably useful.

83. Gravity Investigations

84. Magnetic Methods
• Like gravity methods, these investigations also take advantage of natural
magnetic field associated with the earth and its relation to subsurface
geology.
Controlling property
• The main controlling physical property in magnetic method is magnetic
susceptibility.
Principle
• The magnetic methods are based on the fact that the magnetic bodies
present in the earth’s surface contribute to the magnetic field of the
earth.
• In general, when the magnetic field of the earth or one of its components
is measured on the surface, bodies possessing magnetic moments
different from those of the surrounding rocks contribute to the
deviations in the measured quantities. From the magnetic anomalies, it is
possible to locate anomalous objects.

85. Magnetic Methods
• The different parameters measured during magnetic
investigations are total magnetic field (intensity and
direction) and different space components
• Magnetic surveys have a certain inherit limitations.
Hence for unique and accurate solutions, magnetic
prospecting is often carried out along with the gravity
or other methods.

86. Magnetic Methods

87. Magnetic Methods
Application of magnetic investigations
• For delineation of large structural forms
favorable for the accumulation of oil and gases.
• For detection of and location of faults.
• For locating strongly magnetic iron ores.
• By virtue of their inexpensive nature and easy
operation, magnetic method are widely used for
detection of ore deposits, geological structures.

88. Magnetic Methods

89. Electrical Methods
• Among the methods different geophysical
• Methods electrical method are numerous and
more versatile, They are more popular because
they are successful in dealing with a variety of
problems like groundwater studies, subsurface
structure, and many others.
Controlling Properties
• In electromagnetic methods, electrical
conductivity, magmatic permeability and dielectric
constant of subsurface bodies are the relevant
properties.

90. Electrical Methods

91. Electrical Methods

92. Electrical Methods

93. Electrical Methods
Principle
• Electric methods are based on the fact that the
subsurface formation, structures, ore deposits,
etc. possess different electrical properties.
These differences are investigated suitably and
exploited to draw the necessary conclusion.

94. Electrical Methods
• Electrical resistivity methods, electromagnetic
methods, self-potential methods and induce
polarization methods are the very important
categories of electrical methods.

95. Electrical Methods

96. Electrical Methods

97. Electrical Methods

98. Electrical Methods
Electrical Resistivity Method
• Principle
• The electrical resistivity's of subsurface
formation vary from one another if they are
inhomogeneous and are studied with the help
of resistivity method. In the case of a resistive
subsurface body, current lines move away from
it and in the case of a conductive subsurface
body, the current lines move towards it.

99. Electrical Resistivity method
• Profiling and Sounding are two types of
resistivity investigations. Profiling is done to
detect lateral changes in resistivity. This throws
light on the change in the subsurface lithology
or structure from place to place.
• Sounding is done to determine the vertical
changes in resistivity. In other words, this study
reveals changes in lithology, etc. at a particular
place with increasing depth.

100. Electrical Resistivity Method

101. Seismic Methods
• Controlling Properties
• Elastic property differences in rocks is the controlling property.
• Principle
• Seismic method of study is based on the principle that
subsurface rock formations bear different elastic properties.
Because of this, the velocities of propagation of seismic waves
through the subsurface layers of earth, suffer reflection or
critical reflection arrive at the surface of the earth where they
are detected by geophones. From the time taken by the waves
to travel through the subsurface formation and from the seismic
wave velocities of the media. It is possible to determine the
depth of various elastic boundaries.

102. Seismic Methods
• With the help of geophones fixed at suitable
intervals on the ground, the different seismic
waves reaching the surface are recorded and
from the times of their arrival, time –distance
curves are constructed. The direct waves are the
first to reach the geophones placed between
point and the distance beyond the point is
called the critical distance.

103. Seismic Methods
• Depending upon whether reflected waves or
refracted waves are used in the investigation,
there are two types of methods, namely, seismic
reflection method and seismic refraction
method.
• A geophone an amplifier and a galvanometer
are the basic units required for reflected or
refracted wave registrations.

104. Seismic Methods
• Seismic refraction studies are effective for depths
more than 100m but are not suitable for shallow
exploration
• Refraction methods are employed for investigating
depths from close to the surface to several
kilometer deep. These methods are also followed
for the investigation of deeper crust under seismic
studies.
• Shallow seismic refraction have found effective
application in investigating the suitability of
foundation sites for civil engineering structures.

105. Geophone

106. 106

107. • Seismic Refraction: the signal returns to the surface by
refraction at subsurface interfaces, and is recorded at
distances much greater than depth of investigation
• Seismic Reflection: the seismic signal is reflected back
to the surface at layer interfaces, and is recorded at
distances less than depth of investigation
Refraction Vs. Reflection

114. 0
5
10
15
20
25
30
35
40
45
50
55
60
0 100 200 300 400 500 600
X = 150 ft
Ti=22ms
Distance (ft)
Time(ms)
Seismic Refraction

115. Radiometric Methods
Controlling property
• Natural radioactivity of rocks and ores
• Principle
• The normal radioactivity is different in different types of
rocks. In igneous rocks, it decreases with decreasing
acidity. If rock contains radioactivity ore bodies, such
areas will exhibit very high radioactivity, giving rise to
anomalies during surveys. Thus based on the study of
radioactivity. It is not only possible to distinguish
different rock types but also to detect radioactive ore
bodies. The profile drawn clearly brings out the
subsurface litho logy, structure and ore body.

116. Radiometric Methods

117. Radiometric Methods

118. Radiometric Methods
• Instruments used in radiometric prospecting are called
radiometer. A radiometer consist of three basic components
• (i) a detector
• (ii) an amplifier or recording unit.
• (iii) a power supply unit.
• Radiometric methods of investigation are useful in many ways
• Exploration of radioactive substances such as uranium and
thorium
• Location of some rare minerals
• Geological mapping
• Exploration of oil & gas
• Ground water studies

119. Geothermal Methods
These methods are latest addition to the group of geophysical method.
Controlling Property
• Thermal conductivity
Principle
• Temperature distribution on the surface of the earth is due to three different
sources.
• They are
• (I) heat received from the sun;
• (ii) Heat conveyed from the hot interior of the earth due to conduction and
convection processes.
• (iii) heat due to decay of radioactive minerals in the crust of the earth.
• By applying the necessary corrections, it is possible to eliminate the solar heat
component and also the heat contribution of radioactive mineral decay. When
this is done, the residual values of temperature distribution on the earth’s
surface can be interpreted in terms of subsurface structures, rock formation and
ore bodies. This forms the principle and basis for geothermal method of
investigation.

120. Geothermal Methods
• For the measurement of the temperature on the
surface of the earth, in shallow holes or in deep
bore holes, thermistors thermometers are used.
Other instruments such as crystal detectors and
radiometers are used.
• The geothermal methods find application in
deep structural studies, ore deposits,
groundwater studies, for delineation of salt-
water fresh water interfaces. Etc.

121. Geothermal Methods

122. Geothermal Methods

123. Electrical Resistivity Method
• All geological formations have a property called
electrical resistivity which determines the ease
with which electric current flows through them.
This resistivity is expressed in the units of Ώm
ohms meter and is indicated by the symbol Ώ

124. Electrical Resistivity Method

125. Electrical Resisitivity Measurements

126. Electrical Resisitivity
Measurements

127. Electrical Resisitivity Measurements

128. Electromagnetic Conductivity (EM)

129. Magnetometer Surveys (MS)
Measure relative changes
in the earths' magnetic
field across a site.

130. Electrical Resistivity Method
Factors Influencing Electrical Resistivity
• The various geological factors which influence the electrical resistivity
are ; mineral content, compactness, moisture content, salinity of
moisture and texture of rocks.
• Mineral Content
• Most of the rock forming minerals have high resistivity, whereas
sulphide mineral possess a high conductivity.
• Moisture content
• Moisture may occur in the rock either as ground water or mere
moisture in the pore spaces. Then the resistivity decreases
considerably. But this change is not of the same order in all
formation.
• Further the resistivity of water is dependent on its salt content and
temperature.

131. Electrical Resistivity Method

132. Electrical Resistivity Method
Resistivity method and measurement of Resistivity
• For the principle of the electrical resistivity
method of exploration and for measurement of
resistivity. A high resistive overburden is a
disadvantage for resistivity studies. This is so
because very little current penetrates the ground
which means that the investigation of deeper
layer is not possible.

133. Electrical Resistivity Method
Classification of Resistivity Methods
• The resistivity method are classified as profiling
type, sounding type, and potential type of methods.
• Profiling method is used for measurement of
resistivity in lateral direction. Sounding type in
which measurement are made in vertical direction.
Potential methods are used in ore prospecting and
are of not of engineering relevance.

134. Application of Electrical Resistivity Studies
• From the civil engineering point of view the
‘resistivity’ investigations are useful in solving a
number of geological problems. They are
aimed at
• (i) foundation studies
• (ii) location of suitable building material
• (iii) ground water studies

135. Application of Electrical Resistivity
Studies
• Some of the specific problems are listed below
• To determine the thickness of loose overburden or the depth of
the bed at the site.
• To detect fractures.
• To ascertain the subsurface rock type and their compactness.
• To locate dykes or vein in foundation rocks.
• To know the strike and dip of rocks
• To detect structural defects like foundation rock
• To detect the structural defects like faults at the foundation site
• To locate suitable building material if required near the project site
• To know the ground water conditions.

136. Seismic Refraction Method
• In seismic method of prospecting, artificial exploration
are made and elastic deformation are induced in rock
present in the ground. The propagation of such
seismic(elastic) waves through the geological formation is
studied. Seismic waves are similar to light waves, since
prospecting can be done by making use of direct wave,
reflected waves or refracted waves.
• The two chief types of seismic exploration are by
seismic refraction methods and seismic refraction
methods. Compared to the light waves, the seismic waves
are extremely slow in their velocities. The light have a
velocity of 300,000 km/sec. whereas the seismic wave
velocity is only 0.31 km/s to 0.36 km/sec in air.

137. Factors Influencing Seismic Wave Velocities
• The geological factor which influence the seismic wave
velocities are mainly the composition of rocks, compaction of
rocks, and saturation of rocks with ground water.
• Composition
• The seismic wave velocities depend on the composition of
rocks. This may be inferred from the following example
• Rock type Seismic Wave Velocity
• Granite 4-6 km /sec
• Basalt 5-6.5 km/sec
• Sandstone 1.5 to 4 km /sec
• Limestone 2.5 to 6 km/sec

138. Factors Influencing Seismic Wave
Velocities
Compaction
• This refer to the porosity or fracturing or degree of
consolidation of rock. The velocity of seismic waves in
rocks is influenced considerably by this factor, the wave
velocity is more in denser/ compact formations. This
may be observed from the following data:
• Formation Seismic Wave Velocity
• Loose sand and soil 0.1 to 0.5 km /sec
• Moist Clay 1.5 to 2.5 km/sec
• Sandstone 1.5 to 4 km /sec
• Shale 2.1 to 4 km/sec

139. Factors Influencing Seismic Wave
Velocities
Saturation
• The Seismic wave velocity increases with the increase
of moisture content in the formation. For ex
• (I) Loose soil has a velocity of 0.1 to 0.5 km/sec, while
moist clay has a velocity of 1.5 to 2.5 km/sec
• (ii) Dry sand has a velocity of 0.15 to 0.4
km/sec, while wet sand has a velocity of 0.6 to 1.8
km/sec.

140. Satellite Imageries In Civil Engineering
Projects
• Satellite images provide an economical,
accurate and rapid means of obtaining quick
assessment for any significant construction or
engineering project, e.g., airstrip, bridge,
dam, water, power plant, sewer, industrial
park, canal and storm utilities, etc

141. Satellite Imageries In Civil Engineering
Projects
• One goal is to obtain information
about superficial materials (granular,
cohesive, permeable, non-uniform, etc.),
thickness of the soil mantle, nature of the
bedrock, drainage, presence of unstable
materials and conditions, presence of
subsurface solution cavities, fractures,
joints, faults, etc.

142. Satellite Imageries In Civil Engineering
Projects

143. Satellite Imageries In Civil Engineering
Projects
• Remote sensing data from satellite
sensors, aerial photography and LIDAR is used
in a variety of civil
and environmental engineering
applications, including site selection, resource
mapping, water quality and quantity
monitoring, geotechnical measurements, and
non-destructive testing.

144. Satellite Imageries In Civil Engineering
Projects

145. Satellite Imageries In Civil Engineering
Projects

146. Satellite Imageries In Civil Engineering
Projects
• Satellite Imagery analysis of surficial materials
measures and provides inventory on land and
water resources. It embodies traditional
engineering disciplines of data analysis, photo-
grammetry, and surveying, as well as emerging
areas of image processing, geographic
information systems (GIS) and global
positioning systems (GPS) technologies.

147. References
• Engineering and General Geology :By Parbin
Singh
• Textbook of Engineering Geology :N.Chenna
Kesavullu

148. Thanks !