In this method (Figure 212), the positive contribution of the backfill to the stability of the dam comes from the weight of the backfill above the downstream face of the dam (WR) and from the horizontal ‘at rest’ pressure F generated on the ab plane (Novak 1996). The weight WR is calculated as the product of the backfill density and the area defined by (abcde) of the backfill and its depth (e). The resultant WR is located at the centre of gravity of the area A.

WR = γΑ  e   

Figure 212 Earth pressure ‘at rest’

The horizontal force F acting at h/3 above the base is given by the equation:


Where Ko is the lateral pressure coefficient at rest and h and H are defined in Figure 212. This method is easy to apply but has some drawbacks. In fact, it does not consider the friction at the backfill-concrete interface and the inclination of the F force.