Pore Water Pressure
The pressure of water in the pores of the soil is called pore water pressure (u). The magnitude of pore water pressure depends on:
- the depth below the water table.
- the conditions of seepage flow.
Under hydrostatic conditions, no water flow takes place, and the pore pressure at a given point is given by
u = gw.h
where h = depth below water table or overlying water surface
It is convenient to think of pore water pressure as the pressure exerted by a column of water in an imaginary standpipe inserted at the given point.
The natural level of ground water is called the water table or the phreatic surface. Under conditions of no seepage flow, the water table is horizontal. The magnitude of the pore water pressure at the water table is zero. Below the water table, pore water pressures are positive.