drained shear strength

[gwkwong]

I am confused with basic principal of drained shear strength.

In drained condition, the pore water pressure dissipate and the load will be carried by the soil grain itself. In this case, the effective soil density is the total density of the soil. But if the soil is below the groundwater level, we will have to use the total soil density minus the density of the water to get the effective density of the soil. So what is the mechanism behind this, where the soil is submerged but yet "drained".

 

[BigH]

It is drained in the sense that it has no excess porewater pressures from loadings or changes of stress (or, in the case of heavilly overconsolidated clays, negative porewater pressures).

 

[GeoDocinFL]

"Drained" and "Undrained" do not refer to whether the soil voids contain water. Rather, "drained" refers to a soil state whereby all excess pore pressure has dissipated (generally, long-term conditions). "Undrained" refers to a soil state where excess pore pressure exists (generally, short-term conditions, or the state that exists immediately after loading).