Abstract: Studies have shown that the deposition environment and stress history of different soft clays are different, and so are their anisotropic laws. However, in the current studies, researchers often use a unified law to describe the anisotropic characteristics of different soft clays. To deal with it, a theoretical formula for anisotropic undrained strength is deduced by means of comparison and theoretical analyses based on the results of Hangzhou soft clay from hollow cylinder apparatus (HCA) test and other conventional results from the literatures. Considering two upper limit methods and strength reduction on the failure surface, the stability against basal heave of soft clay excavations is obtained and discussed in terms of application. The influences of geometrical factors such as the depth ratio H/B, embedded length D, friction characteristics of the interface between walls and clays, together with the effective friction, anisotropic strength ratio k and strength heterogeneity, are discussed. Finally, the applicability of the proposed formula is verified from engineering cases.