assumption of rankine theory of earth pressure / lateral earth pressure

 

Assumption Of Rankine’s earth pressure theories

 

Rankine’s theory of lateral earth pressure is applied to uniform cohesion less soil only. Later it was extended to include cohesive soils by Resal (1910) & Bell (1915).

Following are the assumption to rankine’s theory…

1. The soil mass is semi-infinite, homogeneous, dry & cohesion less.

2.The ground surface is a plane which may be horizontal and inclined.

3. The back of the wall is vertical and smooth.

4. The wall yields about the base and thus satisfies the deformation condition for plastic equilibrium.

However the retaining walls are constructed of masonry of concrete, and hence the back of the wall is never smooth. Due to this frictional forces develop. As a consequence of Rankine’s assumption of no existence of frictional forces at the wall face, the resultant pressure must be parallel to the surface of the backfill. The existence of the friction makes the resultant pressure inclined to the normal to the wall at an angle that approaches the friction angle between the soil and the wall.

The following cases of cohesion less backfill will now be considered:

1.  Dry or moist backfill with no surcharge.

2. Submerged backfill.

3. Backfill with uniform surcharge.

4. Backfill with sloping surface.

5. Inclined back and surcharge.