Abstract：Using standard stress path triaxial system，STDTTS+UNSAT(7 kN/1 700 kPa) production of GDS，UK，a series of laboratory tests are conducted with undisturbed muddy clay samples obtained from Shanghai. Time-dependent properties and pore water pressure in passive zone and active zone in excavation are researched. It is shown that three stages appear under unloading：weakening stage，constant speed stage and accelerating stage. Creep curve is in weakening stage when unloading is small and then changes from weakening stage to constant speed stage with the increase of unloading. Soil sample is damaged quickly at high unloading stress level with deformation sharply increased. However，it is not found that creep curve of soil changes with time from constant speed stage to accelerating stage directly. Parameter of pore water pressure is not constant and changes with time. Pore water pressure decreases under unloading whether in passive zone or in active zone of excavation，then increases to the maximum value in undrained creep stage and safety ratio is the smallest at this time.
