Abstract
Five embankments were rapidly constructed on an alluvial marine clay under a very low factor of safety. One embankment failed and two others must have been on the verge of failure. A stability analysis with the total stress method for each embankment was reported by Hanzawa et al. (1980) and showed quite good agreement with the field behaviour of embankments when the undrained strength of the clay was evaluated from the modified Bjerrum's method in considerations of the effects of anisotropy and strain rate.In this paper, a stability analysis with the effective stress method as well as comparison of measured and predicted excess pore water pressure is presented. Excess pore water pressure was predicted using pore pressure coefficient, A-value in consideration of the effect of strain rate on pore pressure behaviour and the predicted values showed good agreement with the measured values in spite of the fact that piezometers were installed in considerably different types of clay. Strength parameters, c' and φ' of the clay are discussed in detail in the light of fundamental properties of normally consolidated aged clay and a procedure for determining c' and φ' for short term stability analysis is proposed. Factors of safety obtained by the effective stress method were 20% to 30% higher than the reasonable values evaluated from the field behaviour of each embankment and strongly suggested the necessity to take consideration of the effects of anisotropy and strain rate in determining c' and φ' for practical stability problems.
