Activity of Regions Below GWT
There are two cases to be considered when deactivating a region below the GWT.
1) The soil subjected to excavation is completely enclosed by active beam elements. The beam is then considered to be impermeable and both the soil and water are removed (removing total stresses - inactive region is free of water). Owing to impermeability of the beam elements, the pore pressure distribution remains unchanged, see the figure.
Pore pressure distribution after removing soil from region enclosed by active beams
2) The removed soil is not enclosed by beam elements. In such case we assume that water in the excavated region is still active. This state is evident from the pore pressure distribution in the figure.
Pore pressure distribution after removing soil
Its effect can be removed by changing the ground water table.
Pore pressure distribution after modifying the ground water table