Undrained stability of pit-in-pit braced excavations under hydraulic uplift

Pit-in-pit (PIP) excavations in an aquifer–aquitard system likely undergo catastrophic failures under the hydraulic uplift, associated undrained stability problem, however, has not been well analyzed past. To this end, a hypothetical model of PIP braced excavation typical soil layers Shanghai, China is developed using finite element limit analysis (FELA) tool. The FELA solutions safety factors (FSs) against uplift are verified with results from strength reduction technique (SRFEA) and existing design approaches. Subsequently, employed to identify triggering failure mechanisms subjected uplift. A series parametric studies considering various geometric configurations excavation, shear strengths aquitard, artesian pressures carried out. sensitivities relevant parameters further assessed multivariate adaptive regression splines (MARS) that capable accurately capturing nonlinear relationships between set input variables output multi-dimensions. MARS-based equation used for predicting FS finally presented artificial dataset practical uses.