Underground water

paper about the underground water and its geotechnical problems and how to control it
This is a large and complex topic and I have to focus on some key points that you need it to finish the project of the tunneling subject that you're working on it

1. Cairo University
Faculty of engineering
4
th
year mining department




Underground water



Submitted To

Prof. Dr. Hassan Fahmy




Submitted By

Ahmed Mohamed Wassel

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Table of contents

1. Introduction. Page 3
2. WORLD’S WATER RESOURCES Page 4
3. The Water Cycle. Page 5
4. Underground water zones. Page 7
5. Groundwater Basics Page 9
6. OCCURRENCE OF GROUNDWATER Page 10
7. Hazards from ground water Page 14
8. Groundwater control Page 16
9. References Page 17

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1) Introduction
Groundwater
All water beneath the land surface is referred to as
underground water (or subsurface water).
Groundwater is the water that saturates the tiny spaces
between alluvial material (sand, gravel, silt, clay)
About 1% of the world's water supply is groundwater, but
this represents 22% of the Earth's supply of fresh water. It
is thus a crucial resource.
Groundwater has its origin in rainfall. Most of it is making
its way slowly back to the ocean, either directly through
the ground or by flowing out onto the surface and joining
streams.

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2) WORLD’S WATER RESOURCES
Of the global water resources, about 97.2% is salt water mainly
in oceans, and only 2.8% is available as fresh water at any time
on the planet earth. Out of this 2.8% of fresh water, about 2.2%
is available as surface water and 0.6% as ground water. Even out
of this 2.2% of surface water, 2.15% is fresh water in glaciers and
icecaps and only of the order of 0.01% is available in lakes and
streams, the remaining 0.04% being in other forms. Out of 0.6%
of stored ground water, only about 0.25% can be economically
extracted with the present drilling technology (the remaining
being at greater depths)

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3) THE WATER CYCLE

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 DURING PART OF THE WATER CYCLE, THE SUN HEATS UP
LIQUID WATER AND CHANGES IT TO A GAS BY THE
PROCESS OF EVAPORATION. WATER THAT EVAPORATE S
FROM EARTH’S OCEANS, LAKES, RIVERS, AND MOIST
SOIL RISES UP INTO THE ATMOSPHERE.


 The process of evaporation from plants is called transpiration. (In
other words, it’s like plants sweating.)



 AS WATER (IN THE FORM OF GAS) RISES HIGHER IN THE
ATMOSPHERE, IT STARTS TO COOL AND BECOME A
LIQUID AGAIN. THIS PROCESS IS CALLED
CONDENSATION. WHEN A LARGE AMOUNT OF WATER
VAPOR CONDENSES, IT RESULTS IN THE FORMATION OF
CLOUDS.


 WHEN THE WATER IN THE CLOUDS GETS TOO HEAVY,
THE WATER FALLS BACK TO THE EARTH. THIS IS
CALLED PRECIPITATION.

 WHEN RAIN FALLS ON THE LAND, SOME OF THE WATER
IS ABSORBED INTO THE GROUND FORMING POCKE TS OF
WATER CALLED GROUNDW ATER. MOST GROUNDWATER
EVENTUALLY RETURNS T O THE OCEAN. OTHER
PRECIPITATION RUNS DIRECTLY INTO STREAMS OR
RIVERS. WATER THAT COLLECTS IN RIVERS, STREAMS,
AND OCEANS IS CALLED RUNOFF.

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4) Underground water zones

UNDERGROUND WATER OCCURS IN TWO
DIFFERENT ZONES [ZONE OFAERATION & ZONE OF
SATURATION]

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 AERATION ZONE: THE ZONE ABOVE THE WATER TABLE IS KNOWN
AS THE ZONE OF AERATION (UNSATURATED OR VADOS E ZONE).
WHICH OCCURS IMMEDIA TELY BELOW THE LAND SURFACE IN
MOST AREAS, CONTAINS BOTH WATER AND AIR.
 The saturated zone: a zone in which all interconnected openings are full of
water .Water in the saturated zone is the only underground water that is
available to supply wells and springs and is the only water to which the name
ground water is correctly applied
Recharge of the saturated zone occurs by percolation of water from the land
surface through the unsaturated zone.
The unsaturated zone is, therefore, of great importance to ground-water
hydrology.
The unsaturated zone may be divided usefully into three parts:
The soil zone, the intermediate zone, and the upper part of the capillary fringe.
 THE SOIL ZONE EXTENDS FROM THE LAN D SURFACE TO A
MAXIMUM DEPTH OF A M ETER OR TWO AND IS THE ZONE THAT
SUPPORTS PLANT GROWT H THE POROSITY AND PERMEABILITY
OF THIS ZONE TEND TO BE HIGHER THAN THOSE OF THE
UNDERLYING MATERIAL .
 THE SOIL ZONE IS UNDERLAIN BY THE INTERMEDIATE ZONE,
WHICH DIFFERS IN THI CKNESS FROM PLACE TO PLACE
DEPENDING ON THE THI CKNESS OF THE SOIL ZONE AND THE
DEPTH TO THE CAPILLARY FRINGE.
 THE CAPILLARY FRINGE : THE SUBZONE BETWEEN THE
UNSATURATED AND SATU RATED ZONES. THE CAP ILLARY
FRINGE RESULTS FROM THE ATTRACTION BETWE EN WATER AND
ROCKS. REGION ABOVE WATER TABLE WHERE WA TER RISES DUE
TO CAPILLARY FORCES IN THE POROUS MEDIUM.
 THE WATER TABLE: IS THE LEVEL IN THE SATURATED ZONE AT
WHICH THE HYDRAULIC PRESSURE IS EQUAL TO ATMOSPHERIC
PRESSURE AND IS REPRESENTED BY THE W ATER LEVEL IN
UNUSED WELLS. BELOW THE WATER TABLE, THE HYDRAULIC
PRESSURE INCREASES WITH INCREASING DEPTH.

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5) GROUNDWATER BASICS
Beds of rock, sediment, and regolith with high porosity (% of
pore space) are better suited to holding groundwater.
Aquifers: Beds that hold large amounts of groundwater.
Types of pore space: Space between grains. (E.g Oglala aquifer.)
Permeability:
Just because pore space exists doesn't mean that water can flow
through it. Pores may be isolated.
Permeability: the ability of a solid to allow fluids to pass through.

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 AN AQUIFER is a geologic unit that can store and transmit
water at rates fast enough supply reasonable amounts to
wells. Unconsolidated sands and gravels, sandstones,
limestones and dolomites, basalt flows, and fractured
plutonic and metamorphic rocks are examples of rock units
known to be aquifers.
 A confining layer is a geologic unit having little or no
intrinsic permeability—less than about 10 Darcy. Confining
layers are sometimes subdivided into aquitards, quicludes,
and aquifuges.
 AN AQUIFUGE is an absolutely impermeable unit
that will not transmit any water.
 An aquitard is a layer of low permeability that can store
ground water and also transmit it slowly from one
aquifer to another.
 An aquiclude is A formation which contains water but
cannot transmit it rapidly enough to furnish a significant
supply to a well or spring.
 The term leaky confining layer is also applied to such
unit. Most authors now use the terms confining layer and
leaky confining layer.

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 Aquifer should yield a significant quantity of water. Thus Porosity and
 Permeability are key factors for a formation to be a good aquifer.
 Important aquifers are made of sedimentary rocks, however igneous and
 Metamorphic rocks may develop very good aquifers.
 Important aquifers may be categorized based on their geology into:
 Alluvial Deposits
 Carbonate Rocks
 Sandstone and Conglomerates
 Igneous and Metamorphic Rocks
 Volcanic Rocks
 Clay

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Aquifers are divided in terms of the nature of their presence to:
Water table or Unconfined Aquifer & Confined, or artesian aquifers

Water-table aquifer or unconfined aquifer is an aquifers with continuous layers
of materials of high intrinsic permeability extending from the land surface to the
base of the aquifer.


Confined, or artesian aquifers, are overlain by a confining layer and recharge to them
can occur either in a recharge area where the aquifer crops out or by slow
downward leakage through a leaky confining layer in the aquifer is under
pressure.

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The potentiometric surface is the representative surface of the level to which
water will rise in a well cased penetrating the confined aquifer (the term
piezometric was used in the past, but it has now been replaced by
potentiometric). If the potentiometric surface of an aquifer is above the land
surface, a flowing artesian well may occur.

A perched aquifer is a layer of saturated soil formed above the main water table
due to trapping water above impervious lenses. Perched aquifers are common in
glacial out wash, where lenses of clay formed in small glacial ponds are present.
Perched aquifers are usually not large; most would supply only enough water for
household use.

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7) Hazards from ground water:
 Porosity of rock :
The pore water can dissolve minerals of the adjacent rock. If it is not flowing,
then the dissolution process stops as soon as the saturation concentration is
reached. However, if fresh unsaturated water is constantly supplied, then the
dissolution does not stop. Thus, cavities (so-called karst) can develop, which can
endanger the stability of buildings1 and cause water inrushes in tunneling
Pore water can physico-chemically affect the rock and can cause some minerals
to swell. By altering the surface tension it can favour the propagation of cracks.
In particular, slates and shales can disintegrate (slake) at contact with water.
This is either due to an increase of the pressure of enclosed air, caused by the
Penetration of water, or to osmotic swelling of the clay minerals

 Pore pressure
The pressure p of groundwater is also expressed as pressure height p/γ
The principle of effective stresses, according to which deformation and strength
of soil are governed by the effective stresses exclusively, also applies to rock
 Inflow in the construction phase
Heading inflows occur when a water-bearing zone is penetrated during tunneling.
Appropriate resources (pumps etc.) must be available on site, because inflows are
very difficult to predict. Water inrush can be critical, especially if the tunnel is
headed downhill or starting from a shaft. The flow rate can be very high (cases
with more than 1,000 l/s are reported), but usually slows down quickly as the
water stored in the rock is depleted

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 To drain or to seal
Tunnels below the groundwater table can be either sealed or drained. Sealed
Tunnels do not influence the groundwater but their lining has to support the
full water pressure
 Drainage
Drainage affects the distribution of hydraulic head by attracting groundwater
and relieving the lining from hydrostatic pressure. The groundwater is then
Collected and appropriately discharged. This needs to be achieved in a
permanent way and maintenance must always be possible. It should be added that
there are tunnels, exclusively devoted to drainage, e.g. to stabilise a slope.
The drainage path of the groundwater is as follows:
1. The groundwater penetrates the shotcrete shell through fissures and adhoc
bored holes (to enhance the mobility of groundwater towards the drainage
system, radial boreholes may be drilled into the ground).
2. The interface drainage systems consist either of fleece (for low discharge) or
of composite geosynthetics or air-gap membranes (for high discharge) and are
placed in the interspace between shotcrete and concrete lining. There are many
types of geosynthetics (so-called geospacers), designed to provide a stable
interspace for water discharge


Generally the ground water may be static ground water or
flowing water in this case it causes a dynamic load

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8) Groundwater control:
 Drainage ore pumping the water from the tunnel
 Prevent the water flow in the tunnel section by air compression or
freezing the water
 Cement: Portland cement is preferably used for watertight
concrete, while blast furnace slag cement produces less heat but
needs longer time for setting.
 Shrinkage: Only a part of the mixing water is chemically bonded
(corresponding to ca 25% of the cement mass). The remaining
water occupies the pores. Thus, a low water content helps to keep
the porosity small. Shrinkage is due to the evaporation of the free
water. Thin parts are more prone to shrinkage, their length
reduction corresponds to the one caused by a temperature
reduction of 15 - 20◦C
 Hydration heat: This is produced during the setting process. The
subsequent cooling may lead to incompatible stressing and, thus,
to fissures. Remedies are late dismantling of formwork, heat
isolating formwork, cooling of the aggregates and of the mixing
water and long (10 - 14 days) moistening of the concrete.

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9) References:
 Basic Ground-Water Hydrology [R. Heath, 1987]
 Advances in Hydrogeology, 2013 [Shlomo P. Neuman,
Alberto Guadagnini, Monica Riva, Phoolendra K.
Mishra, Kristopher L. Kuhlman]
 Geotechnical Engineering of Dams, 1st ed. [Robin Fell,
Patrick MacGregor, D. Stapledon] (Geo Pedia)
 Tunneling and Tunnel Mechanics

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