Download gayakwad pravin soniravbhai

Seminar Topics
on
“HYDROGEOLOGY”
Government Engineering college;
Bhavnagar
November,(2014-2015)
There are following students involve in this
seminar topic… … …
SR.NO.
NAME
EN.NO.
1
GAYAKWAD PRAVIN SONIRAVBHAI
130210106017
2
GHORI PAYAL CHANDUBHAI
130210106018
3
GOHIL DARSHANABA DIPSINH
130210106019
4
GONDALIYA HONEY HARSHDBHAI
130210106020
5
GUJARIYA MAHIPAL BALABHAI
130210106021
6
HADIYAL DHAVAL CHATURBHAI
130210106022
7
JADAV BHAVESH BHANAJIBHAI
130210106024
8
KHASIYA RAKESHBHAI RAJESHBHAI
140213106004
9
PARMAR GAURAV NATVARLAL
140213106008
•INTRODUCTION
•
i.
ii.
iii.
iv.
Ground water may be defined as the underground water that occurs in the
saturated zone of variable thickness and depth, below the earth’s surface. Cracks
and pores in the existing rocks and unconsolidated crystal layer, make up a large
underground reservoir, where part of precipitation is stored.
The study of the ground water is relevant form the civil engineering point of
view from different angles as follows:
As geological agents, ground water contributes to the decomposition of rocks.
This makes the properties of rocks such as competence, durability and
appearance, deteriorates and renders them unsuitable for construction purposes.
Thus, this is a matter of serious concern for a civil engineer.
Formation of solution cavities or channels inside the calcareous rocks is also one
of the undesirable effects of ground water.
Ground water condition prevailing in some regions may seriously jeopardize the
stability of certain civil engineering structures such as dams, reservoir and
tunnels.
In dealing with the water supply for constructional activities, irrigation,
industries, domestic requirements, etc. A civil engineer may have to look
towards ground water as a source of water supply.
•HYDROLOGICAL CYCLE
The hydrological cycle is a descriptive term applied to the circulation
of water from the ocean to the atmosphere, to the ground and back to the
oceans again. Thus, hydrological cycle is the earth’s water circulatory system.
Fig. shows the schematic representation of the hydrologic cycle. The
cycle may be considered to begin with the water of the oceans. Water from the
ocean’s surface is evaporated into the atmosphere. The vapour is condensed by
various processes and falls to the earth as precipitation. Some of this
precipitation falls directly on the land is retained temporarily in the soil, in
surface depressions and on vegetation. Until it returned to the atmospheres by
evaporation and transpiration.
•SOURCES OF GROUND WATER
•
i.
ii.
iii.
The following are the important sources of ground water:
Springs
Infiltration galleries
Karez
•
Springs
A spring is a flow of ground water at the ground surface. A pervious layer,
sandwiched between two impervious layers, give rise to a natural spring. A spring
indicates the outcropping of the water table.
•
Infiltration galleries
An infiltration gallery is a horizontal conduit having permeable boundaries so
that ground water can infiltrate into the same. It is generally provided in highly
permeable aquifers with high water table so that adequate head is available for
gravity flow of ground water into the gallery. Usually a gallery is located at depths
3 to 6m.
Three layers of graded filter around gallery are –
i. 16 cm ballast(25 to 50 mm size) around pipe
ii. 16 cm large pebbles (12 to 24 mm size) as intermediate layers.
iii. 24 cm fine pebbles (3 to 10mm) as the outer layer.
•Karez
A karez is an underground Tunnel driven into the hill side to tap water from the
underground spring. The tunnel has certain bed inclination. Water from the karez is taken
in an open channel. Such channels are in use in Baluchistan and West Pakistan.
• OCCURANCE OF GROUND WATER
•
•
The rainfall that percolates below the ground surface passes through the voids of
the rocks, and joints the water table. These voids are generally interconnected,
permitting the movement of the ground water. But, in some rocks, they may be
isolated, and thus, preventing the movement of water between the interstices. The
mode of occurrence of ground water, therefore, depends mainly upon the type of
formation, and hence depends upon the geology of the area.
The possibility of occurrence of ground water mainly depends upon two
geological features:
i.
The porosity of the rocks.
ii.
The permeability of the rocks.
•ZONES OF UNDERGROUND WATER
•
With respect to the existence of water at different depths, the earth’s crust can be
divided into two major zones, namely
i.
Zone of rock fracture
ii.
Zone of rock flowage
•
Zone of rock fracture
Upon the zone of rock flowage, there lies the zone of rock fracture. In this
zone, the stresses are within the elastic limits, and depend upon porosity. The
maximum depth of this zone below the ground surface varies in the range of about
100m to 1000m or more.
•
Zone of rock flowage
The depth of the zone of rock flowage (i.e. the zone in which the rocks undergo
permanent deformation) is not accurately known, but is generally estimated as
many miles. Interstices are generally absent in this zone, because the stresses are
beyond the elastic limits, and the rocks remain in the state of plastic flow. Water
present in this zone is known as internal water, and a hydraulic engineer has
nothing to do with this water.
•TYPES OF AQUIFERS
• Aquifers are mainly of two types:
i.
Unconfined aquifers
ii.
Confined aquifers
•
Unconfined aquifers
Unconfined aquifers is the one in which water table forms the upper surface
of the zone of saturation. It is also known as water table aquifer or Phreatic aquifer
or non artesian aquifer.
The water table is not a stationary surfaces but it rises when more water
enters the aquifer from natural or artificial recharge, and it drops when recharge is
less and the previously stored water flows out towards springs, streams, wells, etc.
•
Confined aquifer
A confined aquifer is the one in which ground water is confined under
pressure greater than atmospheric pressure by overlying relatively impermeable
strata. It is also known as artesian aquifer or pressure aquifer.
A confined aquifer is analogous to a pipeline. In a well penetrating such an
aquifer, the water level will rise to the level of the local static pressure or artesian
head. Confined aquifers have small recharge area as compared with unconfined
aquifers.
•GEOLOGICAL CONTROLS OF GROUND
WATER MOVEMENT
•
1.
2.
3.
4.
Ground water movement in the one of aeration takes place under the influence of
gravity. But the factors influencing water movement in the zone of saturation are of
different kinds. Most of them are geological and are as follows:
The permeability of rocks in one of the most influencing factors of ground
water movement.
The most important geological control is the kind of secondary porosity
associated with the rocks. Well-developed joints, if present guide the movement
of ground water along their alignment. Sheet joints are sometimes very important
in this regard. Similarly, faults, if present, also influence the ground water to
move along them. This is the reason for the alignments of springs, noticed in
some places.
Attitude of bedding is also an important factor affecting ground water
movements. Generally, different sedimentary beds differ in their permeability;
some may be impermeable too. If such beds occur inclined or folded (into
anticlines and synclines) the percolated water moves along the bedding planes
only, i.e. not vertically downwards as usual under the influencing of gravity. The
artesian conditions occur in this way only.
The buried river channels and unconformities also influence the ground water
movement as they are more porous and permeable.
5.
Relatively small pockets of zones of saturation occur within the zone of aeration as
perched water bodies only due to the prevention of movements of vedose water by the
locally occurring impermeable formation.
6.
Occurrences of vertical or steeply inclined dolerite dyles, quartz veins, etc. Which
are relatively harder and resistance than the associated country rocks, may act as
barriers to the natural flow of ground water. This makes ground water occur in plenty
on one side of the dykes and very less on the other side.
7.
Hydraulic gradient (i.e. slope or difference in water table level) also affect the
ground water movement.
•GROUND WATER EXPLORATION
•
Ground water does not occur everywhere below the earth’s surface. “Ground
water prospecting” means searching for the ground water. Ground water
prospecting is a complicated process. It involves a detailed geological survey of the
area followed by more elaborate geophysical investigations.
There are two different approaches: One by water dividing and the others by
scientific studies. Water dividing is a simple, inexpensive and instantaneous method
in which some people endowed with some extraordinary sixth sense are capable of
pinpointing the places where ground water occurs. They do not make use of any
instrument except a small y-shaped twinge sometimes. Their findings, even if they
are true, do not represent any logic or reason. It is purely a personal ability which is
beyond questioning or analysis. Thus, as it has no scientific basis, it is improper, not
authentic and liable to cheating too.
The other method is scientific which stands up to scruting and reasoning. Standard
equipments, procedure and interpretation techniques enable it to be followed by anyone
carrying out ground water exploration.
Ground water investigations are of three kinds:
1. Geological Investigations
2. Geophysical Investigations
3. Hydrological Investigations.
•GROUND WATER IN CIVIL
ENGINEERING PROJECTS
•
i.
ii.
iii.
iv.
1.
The safety, economy, design and construction of all major civil engineering
projects like dams, reservoir, tunnels, bridges, highways, etc. are intimately related
to ground water conditions of the area in which projects are located. It is therefore,
a matter of importance that the projects engineer obtains fullest possible
information through direct and indirect exploration and investigations about,
Position of water table
Types of aquifers
Condition of aquifers
Hydraulics characteristics of rocks, etc.
Dams and Reservoir
The main purpose of constructing a dam across a river is to store water in the
form of reservoir on its upstream side. The whole idea of a dam would become
irrelevant if the foundation on which it is built are made of porous rocks or if a
stretch of a reservoir adversely. Also leaking water may initiate failure at the
abutments or even under the dam in a number of ways.
2. Tunnels
Tunnels are the underground passages, used either for traffic or for the conduct of
water. In the length of tunnels, following anyone of the situations may exist:
i. The entire length of tunnel is located above the water table.
ii. The entire length of tunnels is located below the water table.
iii. The alignment is partly above and partly below the water table.
Obliviously, the design, construction and maintenances of a dry tunnel will demand
entirely different types of considerations than for wet or partially wet tunnels. Thus, the
knowledge of ground water conditions around the tunnel alignments is very important.
3. Highways and cuts
Ground water may present very complex problems in laying out highways and air
fields. In either case, the site is considered unsafe and unsuitable if the water table is very
high. Some sort of reliable underground drainage system must be provided if the site has to be
selected at any cost.
Similarly, ground water is a major source of trouble for the stability of slopes. Many
slope failures especially in hilly areas are due to involvement of ground water. Soil creep and
liquefaction mainly occur due to ground water. The lubricating action of water along joints of
rocks is the major causes of landslides.