Vertical stress in soil mass

In fluids forces acting on a point are same in all  the directions. But in soil it's not like that. 

To develop this theory we have 2 assumptions,
1). Soil plane is horizontal
2). dry soil condition














Vertical stress (total stress) at considered point A from a height of h,

Basically soil is particulated medium, (medium with small particles have all 3 phases solid, air and water) for such soil condition we need to use gamma wet instead of gamma dry.

But below the water table there is no air therefore, for soil under water table we need to use gamma sat.