Abstract: The design of braced excavations in soft clays is usually controlled by the short-term undrained stability.The principal stress axial rotation induced by excavation and the undrained anisotropic soil strength were taken into consideration.Assuming the Prandtl soil slip failure modes and considering the anisotropic soil strength recommended by Casagrande and Carillo and the non-homogeneous feature of soft soil,a calculation method for evaluating the basal stability was proposed based on the upper bound analysis.It was indicated by the numerical results that the basal stability was significantly influenced by the anisotropy ratio of soil,the plane geometry of the excavation as well as the thickness of soft soil layer between excavation base and hard stratum.The results were also compared with those calculated by numerical methods.The present method was verified by the field observations of braced excavations.