An Investigation on Stability Analysis of Cut Slopes in Clays

Abstract

When a cut slope is constructed in a saturated clay ground, pore water pressure decreases instantly due to unloading. With time, the ground will expand gradually and the pore water pressure will rise towards long-term state. During this process, air may be absorbed into the slope; consequently, an unsaturated zone appears in the vicinity of the ground surface. In simulating such a swelling process, most existing FE methods neglect the air ingress into the slope and the whole analysis region is assumed saturated. However, this assumption leads to erroneous results, i.e., the factors of safety for assumed slip circles may increase with time; this is discussed in the first half of the text on the basis of illustrative examples. It is inferred that the erroneous results come from the improper assumption of the only saturated analysis. Hence, in the last half of the paper we employ a three-phase saturated-unsaturated model incorporated with an elasto-plastic constitutive relation to take into account the appearance of the unsaturated zone during swelling. This model is applicable not only for saturated problems but also for unsaturated ones. The results indicate that the proposed method can correctly represent the soil behavior of cut slopes, therefore, leading to the conclusion that the only saturated analyses are not adequate for cut slope problems.