The Basal Heave Stability Analysis of Braced Excavations in Soft Soils Using Numerical Methods

Basal heave instability is one of the deep excavation failures in soft clay. This type of instability usually occurs immediately after excavation and should be controlled according to a short term analysis (undrained). In order to evaluate the base stability of excavations, numerous equations have been developed by various researchers based on the limit equilibrium theory. The differences among these methods are in terms of the failure mechanisms and simplified assumptions. Despite extensive academic and practical use of these equations, some uncertainties can yield results with doubtful levels of accuracy. In this paper, the basal heave stability is evaluated using the finite element method, and the results are compared with the safety factor obtained from equations based on limit equilibrium analyses such as the Terzaghi equation (which considers wall embedded depth), the Eide et al. equation and the Japan Code method (resisting moment). Using a sensitivity analysis, the effect of various parameters on the results from these methods is then investigated. The results indicate that the safety factors from the numerical analyses are in good agreement with those obtained from the resisting moment method. Moreover, using the Terzaghi equation in basal heave stability analyses yields underestimated results.