Technical University of Mombasa
DCE 2202 GEOTECHNOLOGY II
Lecturer : Jackson Muruda
Email :
LATERAL EARTH PRESSURE
Introduction:
Structure in the ground or in contact with natural ground or fill material may be subjected
to either vertical and horizontal pressures (or forces) from the ground.
The lateral pressures and forces in the ground are related to the vertical pressures and
forces and a knowledge of both sets of forces is needed in order to design structure in the
ground.
Lateral earth pressures may be very large, even at fairly shallow depths. Unless adequately
accounted for in design they will cause failure of the structure.
Lateral earth pressures are frequently encountered in the design of basements (cellass) and
retaining structure although they are also important in many other types of structures such
as pipes and tunnels.
DEFINITIONS
1. ACTIVE PRESSURE
Occurs when a structure (e.g. a vertical retaining wall) moves away under the action of
pressure from retained soil. The lateral pressure from the soil reduces to a minimum
value:
THE ACTIVE EARTH PRESSURE
1
,2. PASSIVE PRESSURE
Occurs when a structure (e.g. a vertical retaining wall) is pushed towards a mass of
retained soil.
The lateral resisting pressure from the soil increases to a maximum value]
THE PASSIVE EARTH PRESSURE.
3. AT REST PRESSURE
Is pressure on a structure (e.g. vertical retaining wall) when there is no movement of the
structure relative to the soil mass.
Elastic and Plastic Equilibrium
A body is said to be in a state of elastic equilibrium when a small increase in a stress acting on
the body causes a corresponding small increase in strain.
The relationship between the amount of strain induced and the causative stress is known as
elastic modulus, e.g. Yong’s direct stress modulus (E), shear modulus (G), volumetric Bulk
modulus (K).
While in a state of elastic equilibrium, the stresses at any point in the body may be represented
by Mohr’s circle of stress.
2
, The shear stress acting on a given plane at angle is given by the ordinate to the circle as
shown.
In an increasing-stress situation a surface of shear failure will develop as the shear stress at
some point in the body reaches the limiting value of shear strength of the material.
Subsequently, a small increase in stress will cause a steady increase in the corresponding
strain, producing a condition known as plastic slow.
Immediately prior to the onset of the plastic flow condition the body is said to be in a state of
plastic equilibrium.
Thus a state of plastic equilibrium implies a set of limiting condition prior to failure.
In fact, two such sets of conditions can arise within a mass of soil or other granular materials
depending on the nature of the lateral strain. The weight of a soil mass generally produces
lateral expansion, leading to a plastic equilibrium and failure condition which is described as
active.
On the other hand, lateral compression tends to be resisted by the weight of soil, so that
subsequently a passive condition is reached.
In design of earth-retaining structures it is necessary first to evaluate the magnitude and
distribution of lateral earth pressures in relation to particular sets of structural conditions.
There are two main theories of earth pressure, one due to Rankine (1857) and the other by
Coulomb (1776).
3
DCE 2202 GEOTECHNOLOGY II
Lecturer : Jackson Muruda
Email :
LATERAL EARTH PRESSURE
Introduction:
Structure in the ground or in contact with natural ground or fill material may be subjected
to either vertical and horizontal pressures (or forces) from the ground.
The lateral pressures and forces in the ground are related to the vertical pressures and
forces and a knowledge of both sets of forces is needed in order to design structure in the
ground.
Lateral earth pressures may be very large, even at fairly shallow depths. Unless adequately
accounted for in design they will cause failure of the structure.
Lateral earth pressures are frequently encountered in the design of basements (cellass) and
retaining structure although they are also important in many other types of structures such
as pipes and tunnels.
DEFINITIONS
1. ACTIVE PRESSURE
Occurs when a structure (e.g. a vertical retaining wall) moves away under the action of
pressure from retained soil. The lateral pressure from the soil reduces to a minimum
value:
THE ACTIVE EARTH PRESSURE
1
,2. PASSIVE PRESSURE
Occurs when a structure (e.g. a vertical retaining wall) is pushed towards a mass of
retained soil.
The lateral resisting pressure from the soil increases to a maximum value]
THE PASSIVE EARTH PRESSURE.
3. AT REST PRESSURE
Is pressure on a structure (e.g. vertical retaining wall) when there is no movement of the
structure relative to the soil mass.
Elastic and Plastic Equilibrium
A body is said to be in a state of elastic equilibrium when a small increase in a stress acting on
the body causes a corresponding small increase in strain.
The relationship between the amount of strain induced and the causative stress is known as
elastic modulus, e.g. Yong’s direct stress modulus (E), shear modulus (G), volumetric Bulk
modulus (K).
While in a state of elastic equilibrium, the stresses at any point in the body may be represented
by Mohr’s circle of stress.
2
, The shear stress acting on a given plane at angle is given by the ordinate to the circle as
shown.
In an increasing-stress situation a surface of shear failure will develop as the shear stress at
some point in the body reaches the limiting value of shear strength of the material.
Subsequently, a small increase in stress will cause a steady increase in the corresponding
strain, producing a condition known as plastic slow.
Immediately prior to the onset of the plastic flow condition the body is said to be in a state of
plastic equilibrium.
Thus a state of plastic equilibrium implies a set of limiting condition prior to failure.
In fact, two such sets of conditions can arise within a mass of soil or other granular materials
depending on the nature of the lateral strain. The weight of a soil mass generally produces
lateral expansion, leading to a plastic equilibrium and failure condition which is described as
active.
On the other hand, lateral compression tends to be resisted by the weight of soil, so that
subsequently a passive condition is reached.
In design of earth-retaining structures it is necessary first to evaluate the magnitude and
distribution of lateral earth pressures in relation to particular sets of structural conditions.
There are two main theories of earth pressure, one due to Rankine (1857) and the other by
Coulomb (1776).
3
