Cairo University Faculty of engineering 4th year mining department

Underground water

Submitted To

Prof. Dr. Hassan Fahmy

Submitted By

Ahmed Mohamed Wassel

2 | P a g e

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

3 | P a g e

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.

4 | P a g e

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)

5 | P a g e

3) THE WATER CYCLE

6 | P a g e

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 EVAPORATES

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 POCKETS OF

WATER CALLED GROUNDWATER. MOST GROUNDWATER

EVENTUALLY RETURNS TO THE OCEAN. OTHER

PRECIPITATION RUNS DIRECTLY INTO STREAMS OR

RIVERS. WATER THAT COLLECTS IN RIVERS, STREAMS,

AND OCEANS IS CALLED RUNOFF.

7 | P a g e

4) Underground water zones UNDERGROUND WATER OCCURS IN TWO DIFFERENT ZONES [ZONE OFAERATION & ZONE OF SATURATION]

8 | P a g e

AERATION ZONE: THE ZONE ABOVE THE WATER TABLE IS KNOWN

AS THE ZONE OF AERATION (UNSATURATED OR VADOSE ZONE).

WHICH OCCURS IMMEDIATELY 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 LAND SURFACE TO A

MAXIMUM DEPTH OF A METER OR TWO AND IS THE ZONE THAT

SUPPORTS PLANT GROWTH 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 THICKNESS FROM PLACE TO PLACE

DEPENDING ON THE THICKNESS OF THE SOIL ZONE AND THE

DEPTH TO THE CAPILLARY FRINGE.

THE CAPILLARY FRINGE: THE SUBZONE BETWEEN THE

UNSATURATED AND SATURATED ZONES. THE CAPILLARY

FRINGE RESULTS FROM THE ATTRACTION BETWEEN WATER AND

ROCKS. REGION ABOVE WATER TABLE WHERE WATER 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 WATER LEVEL IN

UNUSED WELLS. BELOW THE WATER TABLE, THE HYDRAULIC

PRESSURE INCREASES WITH INCREASING DEPTH.

9 | P a g e

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.

10 | P a g e

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.

11 | P a g e

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

12 | P a g e

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.

13 | P a g e

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.

14 | P a g e

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

15 | P a g e

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

16 | P a g e

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.

17 | P a g e

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

_____________________________________________