Abstract: To investigate the stability of the expressway embankment on soft ground, the whole arc method is used to deduce a limit equilibrium equation with coupling variables of internal friction angle and cohesion .The effect of internal friction angle on the tangential direction of slip surface is then assumed equivalent to cohesion effect, and the concept of equivalent cohesion is proposed. Based on the limit equilibrium equation and the equivalent cohesion, a procedure to calculate the optimal section size of loading berm is developed. The proposed procedure is used to design the section size of the loading berm and to determine the safety factor for a expressway embankment, and the calculated results are compared with the method from the code. The results show that because the combining effect of internal friction angle and cohesion is considered, the proposed procedure has a greater advantage in acquiring the optimal section size of loading berm than the method recommended by the code, in which only cohesion is considered. The safety factor calculated by the proposed method is 1.05, which agrees well with the results obtained with the method from the code. The proposed method can avoid the shortcomings of traditional methods that require experience in determining the size of berm.

Key words: loading berm, fill embankment, soft ground, sliding surface, stability analysis