Definition - What does Effective Stress mean?
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.
While adopting trenchless construction methods such as horizontal directional drilling (HDD), horizontal auger boring (HAB), direct pipe, microtunneling etc., it is necessary to derive the effective stress of the soil in the proposed project site to determine the kind of drilling technique suitable for the project and to prevent failure.
Trenchlesspedia explains Effective Stress
The total stress and pore water pressure depend on the position of the groundwater. Seasonal variations can cause the water table to move up or down, resulting in a change in the pore water pressure. When water level rises below the ground, pore water pressure increases causing a decrease in effective stresses; dip in the water level, decreases pore water pressure, increasing the effective stress of the soil.
In the case of a change in the water level above ground, effective stresses do not change because a rise or fall above ground will increase or decrease respectively both pore water pressure and total stress. Therefore if total stress and pore water pressure vary by the same amount, the effective stress does not change or is constant.