Abstract
A three-dimensional slope stability problem involving a spherical failure surface in clay is often used in the literature as a benchmark example against which numerical models are validated. In the existing research literature, the analytical expression has been obtained for the factors of safety by assuming plane-strain mechanisms during slope failure. And the hypothesis does not comply with the actual project due to the size effect of slope and surrounding constraints placed on the slope. This paper compares and analyzes the results of the existing research literature. And the three analytical expressions under the three kinds of rotational model have been given for the factors of safety. In practice, the value of factor of stability obtained by numerical model should be in a range which is determined by rotational model of failure body. In this paper, when subtended angel is equal to 60° , the value of factor of stability obtained by numerical model for benchmark example should be reasonable in the range from 1.191 to 1.588.