Permeability of soil

1. Permeability of Soil & Seepage Analysis
Geo-Technical Engineering-1
Aldel Education Trust
St John College of Engineering and Management, Palghar
Mr. Naveen H

2. Detailed Syllabus
○ Introduction about groundwater flow: water table, types of aquifers, types of
soil water, explanation of surface tension with capillary rise in small diameter
tubes, capillary rise in soils
○ Definition of hydraulic head, hydraulic gradient, Darcy’s law, laminar flow
through soil, validity of Darcy’s law.
○ Definition of permeability of soil, numerical values for different types of soils,
determination of coefficient of permeability of soil in lab using constant head
and variable head methods. Determination of in-situ permeability with
pumping out and pumping in test. Permeability from indirect methods e.g.
empirical equation & from consolidation data

3. Detailed Syllabus
● Permeability of stratified soil deposits
● Definition of seepage and its importance for the study of analysis &
design of hydraulic structures. Derivation of Laplace equation for two-
dimensional flow, its analytical solution representation by stream &
potential function; Graphical representation by flow net, definition of flow
line, equipotential lines, flow channel, field, characteristics of flow net, use
of flow net
● Solution of Laplace equation by other methods e. g. numerical methods

4. Introduction about groundwater flow
Water present in the voids of soil mass is called soil water. It can be classified
in several ways given below:
a. Broad Classification
● Free Water
● Held Water
➢ Structural Water
➢ Adsorbed Water
➢ Capillary Water

5. Types of Soil water
b. Classification on Phenomenological basis
● Ground Water
● Capillary Water
● Adsorbed Water
● Infiltered Water
c. Classification on Structural Aspect
● Pore Water
● Solvate Water
● Adsorbed Water
● Structural Water

6. Ground water

7. Ground water
It is subsurface water that fills the voids continuously and is subjected to no forces other
than gravity. Hence this water is also known as gravitational water or Free water.
It is that water which is lifted up by surface tension above
the free ground water surface.This water is in suspended
condition within which the interstices and pores of
capillary size of the soil.
The capillary water fill all the pores in the soil, to a certain
distance above the water table- this distance being known
as zone of capillary saturation.
Capillary Water

8. Adsorbed Water
Adsorbed water comprises of
(i) Hygroscopic water
(ii) Film water
Hygroscopic water : Hygroscopic water r contact water or surface bound moisture is that
water which the soil particles freely adsorb from atmosphere by the physical forces of
attraction and is held by the forces of adhesion
film water : film is attached to the surface of the soil particles as a film on the layer of
hygroscopic film.
Infiltrated water : it is that portion of a surface of precipitation which soaks into ground
moving towards through air containing zones. it is subjected to capillary force.
Pore water :

9. Capillary Water
Capillary water is water held in the
micropores of the soil, and is the water that
composes the soil solution. Capillary water
is held in the soil because the surface
tension properties (cohesion and
adhesion) of the soil micropores are
stronger than the force of gravity.
However, as the soil dries out, the pore
size increases and gravity starts to turn
capillary water into gravitational water and
it moves down.

10. Surface tension
Surface tension of water is the property which exists
in the surface film of water tending to contract the
contained volume into a form having a minimum
superficial area possible.
The molecules on surface of a liquid are attracted by
other molecules on the surface and inside the body
of the liquid. Because there is no pull from outside,
the surface molecules are pulled towards the inside
of the liquid mass tending to reduce the surface the
to a minimum.

11. Seepage Analysis-Laplace Analysis.
Derivation of Laplace equation for two- dimensional flow
Derivation of Laplace equation for two- dimensional flow

12. Flow Net
Flow line : A Flow net is a graphical representation of
flow of water through a soil mass. It is a curvilinear
net formed by the combination of flow lines and
equipotential lines. A line along which a water particle
moves through a permeable soil medium.
Equipotential lines: Flow lines represent the path of
flow along which the water will seep through the soil.
Equipotential lines are formed by connecting the
points of equal total head.
Flow channel: Strip between any two adjacent Flow
lines.
NOTE:Flow Lines and Equipotential Lines must meet at right angles

13. Properties of flow net are as follows:
● The angle of intersection between each flow line and an equipotential line
must be 90o which means they should be orthogonal to each other.
● Two flow lines or two equipotential lines can never cross each other.
● Equal quantity of seepage occurs in each flow channel. A flow channel is a
space between two flow lines.
● Head loss is the same between two adjacent potential lines.
● Flow nets are drawn based on the boundary conditions only. They are
independent of the permeability of soil and the head causing flow.
● The space formed between two flow lines and two equipotential lines is called
a flow field. It should be in a square form.
● Either flow lines or equipotential lines are smoothly drawn curves

14. Flow net

15. Graphical Method