Effective stresses:
In a deposit of fine sand the water table was at 3m below the ground surface but the sand up to a height of 1m above the water table was saturated by capillary rise. The sand above this height can be considered as dry. For the sand G_s = 2.65 and n = 40%. Calculate the effective stress at a depth 8m below the ground surface.
Solution
Effective stresses
NOTE
What is the pore water pressure?
Pore water pressure is the pressure of groundwater held between soil or rocks in the gaps (or ‘pores’) between particles. It is affected by the soil type, water flow conditions and level of the water table.
Effective stress can be defined as the stress that keeps particles together. In soil, it is the combined effect of pore water pressure and total stress that keeps it together. It can also be defined in equation form as the total stress minus the pore pressure.
Total stress at a point is defined as the sum of the stress exerted by the total weight (solids plus water) of the soil/rock and the load on the foundation.
