The hetergeneity of soil is a common phenomenon in geotechnical engineering. In view of the characteristic of the soil stability during excavation in soft clay

an upper-bound limit analysis method is used to solve the problem of basal stability in heterogeneous soft soil. The applicability of the upper-bound method is discussed to ensure that it obeys the requirements of the limit analysis theorems. Prandtl mode of the bearing capacity of foundation is then adopted to construct a kinematically admissible velocity field for the upper-bound method. Based on the kinematically admissible velocity field

the calculation formulas for the basal stability in heterogeneous soft soil are established. With the proposed formulas

the effect of the soil strength

the width of foundation pit

the depth of retaining wall and the location of the hard stratum on the stability coefficient are discussed. The basal stability of several cases is studied and the calculated safety factors are compared with those obtained by other methods. The comparison demonstrates the applicability of the upper-bound method used in this paper.