Abstract: The anisotropic properties of soft clays are closely related to the sedimentary environment and stress history. Based on a theoretical formula of anisotropic undrained shear strength which take soft clay characteristics into account, this paper analyzes the soft clay stability against basal heave with slip circle method with consideration of strength reduction on the failure surface. The considered strength reduction formula can be expressed as , which means shear strength on the failure surface equals to the undrained shear strength times the cosine value of effective internal friction angle. Stability against basal heave of excavation is studied. Based on a number of examples, the influences of geometrical factors such as the excavation depth H, embedded depth D, and relative distance of the lowest support to the pit bottom He/H are analyzed. Strength factors such as the effective internal friction angle , anisotropic strength ratio k and slope of heterogeneous shear strength versus depth are also investigated. Finally, the applicability of the formula is verified by the engineering example. This paper provides a new idea for the stability analysis against excavation basal heave.

Key words: sofy clay, undrained shear strength, the anisotropy strength ratio, the arc sliding method, principal stress axis angle