Abstract: The seepage analyses in unsaturated soils are performed at a ground anchor supported deep excavation site by using MIDAS GTS finite element software under the different precipitation conditions. In order to simulate the matric suction dissipation in the unsaturated soils, two rainfall modes are considered in the numerical analysis: transient storm rain and prolonged light rain showers. Under a short period of intensive storm rain, a transient saturated soil zone will be developed underneath the slope surface and the matric suction at deeper soil has little change, whereas, the prolonged light rain showers will gradually saturate the entire slope. The pore water pressure developed from the prolonged rain fall is then introduced into the excavated slope model and the stability is analyzed by using the strength reduction method. It is concluded that the prolonged rainfall has larger impact on the stability of the supporting structures and overall stability of deep excavations.

Key words: transient and intensive storm rains, prolonged light rain showers, MIDAS GTS, slope stability