- What is the difference between the lateral earth pressure of water and soil?
- The shear strength of water is zero, hence but the shear strength of the soil is not zero hence
- For all material where “K” is constant. For water K, but for soil „K‟ depend upon the type of soil, the direction of wall movement, and the amount of wall movement.
- Retaining wall is used to retain the soil as the soil can‟t be self retain if the angle is greater than “angle of repose”.
- In the design of these retaining structures, it becomes imperative to know the magnitude and line of action of earth pressure, where earth pressure is the lateral force exerted by the soil on any structure retaining the soil
Lateral earth pressure is the pressure that soil exerts in the horizontal direction. … Active Earth Pressure Active earth pressure occurs when the wall tilts away from the soil. (for example a typical free-standing retaining wall) • In Active earth pressure the value of K is minimum.
Type of Lateral Earth Pressure
(A) Earth Pressure At Rest⇒ Wall does not move at all i.e zero lateral strain.
(B) Active Earth Pressure⇒ Wall moves away from the backfill soil. The pressure on the wall get reduced and after
a particular displacement of the wall the pressure reaches a minimum value.
(C) Passive Earth pressure⇒ Wall moves towards the backfill soil. The pressure on the wall increases and reaches
a maximum value.
Earth Pressure at Rest
Under conditions where there is no lateral strain within the groundmass, the value of the lateral soil pressure is commonly called the lateral earth pressure at rest (K0). Sometimes it is also defined as the neutral lateral earth pressure or the lateral earth pressure at consolidated equilibrium.
- At rest, lateral pressure is the value of the pressure existing in a soil deposit in its natural state that has not
- been yielding laterally.
- Normally consolidated soils are soils at rest.
- The lateral strain is 0 when the soil is at rest.
- depend upon (a) formation of soil deposit (b) Angle of friction (c) Density Index (d) Stress history
- For Cohesionless soil or NC soil.
- When soil is at rest, it is not in Limiting equilibrium but it is in Elastic Equilibrium.
- for various soil is (a) Dense sand =0.45 (b) Loose sand=0.5 (c) N.C Clays=0.65 (d) O.C Clays=2.5-4
Limiting Equilibrium or Plastic Equilibrium ⇒ When every part of a soil mass is just on the verge of failure the soil
is said to be in limiting equilibrium or Plastic equilibrium. The soil at rest is not in limiting equilibrium but soil at the active state and passive state is in limiting or plastic equilibrium.
Active Earth Pressure
Active earth pressure is the earth’s pressure when the wall retaining the soil moves away from backfill. Because of the movement of wall soil mass adjacent to the retaining wall tends to break away from remaining soil mass. Passive earth pressure is the earth pressure exerted when the wall moves towards the backfill.
- If there is a movement of the wall away from the soil, it decreases as the soil fall below. decreases to a minimum value such that a state of plastic equilibrium develops.
- since the active state is developed by a decreasing of this must be the minor principal stress and the vertical stress is a major principal stress.
Passive Earth Pressure
- If the movement of the wall is towards the soil, there will be lateral compression of the soil, and the value of will increases until a state of plastic equilibrium develops.
- Since passive state develops with an increase in, this must be major principal stress and is minor
- principal stress.
- Inactive as well as passive remains the same, but there is a change in h.