Evaluation of stability against basal heave for excavations in clay overlying a confined aquifer

Base instability caused by high artesian pressure is one of the most serious threats to braced excavations in an aquifer-aquitard system. Accordingly, this study conducted stability analysis utilizing the finite element method with shear strength reduction (SSRFEM). The SSRFEM model was established to investigate base stability for braced excavations in clay overlying a confined aquifer for both undrained and drained conditions. Then, the failure mechanisms of the braced excavations in the clay overlying the confined aquifer were investigated systematically. Numerical simulation results revealed three typical failure mechanisms corresponding to different artesian pressures: circular sliding, overall upwards movement, and the combined mode. Excavation width is an essential factor affecting the critical artesian pressure, while the wall strength and the embedment depth of the wall have little effect. Finally, a new simplified method for evaluating the base stability against hydraulic uplift was proposed. The effectiveness of the proposed method within the scope of application was demonstrated by comparing it to SSRFEM and the pressure balance method. The results obtained by the pressure balance method are conservative, especially for narrow excavations.