Plasticity limit analysis of stability of embankment fill on layered soft soil ground

The stability of embankment fill on layered soft soil ground is analyzed. For each layer of soft soil, arbitrarily linearly increasing undrained shear strength with depth is considered. According to the deep-seated failure mode revealed from engineering practice, a logarithmic spiral and an arc combined rotational failure mechanism is constructed for the fulfillment of the kinematical admissibility based on the upper bound theory of plasticity limit analysis. The methods for the analysis of the critical embankment height, non-dimensional stability number, stability charts, the minimum factor of safety and the critical slip surface are established for rapid evaluation of the stability of embankment fill on layered soft soil ground. Comparisons are made of the calculated results with the measured ones from two case histories of field tests of embankment failure. It is shown that the minimum factor of safety derived from the proposed method is basically identical to the theoretical value of 1.0 of the minimum factor of safety for embankment instability. The critical slip surface determined by the proposed method is approximately consistent with the measured one. The applicability of the proposed method is thus verified.