Introduction

This example simulates an excavation in stages below the water table. The prime objective is to look at the change in pore-water pressures, and the possibility of creating negative pore-water pressures due to the unloading.

A secondary purpose is to demonstrate and check on the use of a moving hydraulic boundary condition on the excavation face. The pore-water pressures on the excavation face are unknown – they could be negative, or it is possible that a seepage face could develop.
Regardless, a special algorithm is required to establish the correct boundary condition as part of the solution.