A modified Prandtl upper-bound solution of basal stability for narrow-deep excavations in undrained clay

Abstract

In recent years, the construction of narrow-deep excavations has been steadily developing. Narrow-deep excavations exhibit a clear size effect in the basal heave stability analysis. However, the classical Prandtl mechanism ignores the size effect and influence of the inserted depth of wall penetration. Based on this, a modified Prandtl failure mechanism that considers the above factors was proposed in this study. Subsequently, a practical equation was derived to simplify the analysis process and obtain the safety factor against basal heave. The upper-bound solution provides a convenient and concise method for basal heave stability analysis of narrow excavations in undrained clay, and its feasibility was verified by comparing it with the results obtained by finite element limit analysis. The results showed that the proposed failure mechanism can provide a better upper-bound solution for the safety factor of the basal stability of narrow excavations than the classical Prandtl failure mechanism.