Effective Stresses Due to Geostatic Stress Fields
The effective stress in a soil mass not subjected to external loads is found from the unit weight of the soil and the depth of groundwater. Consider a soil element at a depth z below the ground surface, with the groundwater level (GWL) at ground surface (Figure. The total vertical stress is
Values of x for a silt at different
degrees of saturation.
Soil element at a depth z with groundwater
level (a) at ground level and (b) below ground level.
The porewater pressure is
and the effective stress is
If the GWL is at a depth zw below ground level (Fig. , then
The effective stress is