Generation of negative excess pore-water pressure (NEPWP) due to the excavation of saturated soils under undrained conditions and the dissipation that follows over time may result in different short- and long-term slope instability. The NEPWP generated due to excavation gradually decreases towards equilibrium or, in some cases, steady seepage. Hence, total pore-water pressures immediately after excavation are lower than the ultimate equilibrium values, leading to a reduction of the average effective stresses in the slope and subsequently threatening stability in the long term. In this research study, the stability of three benchmark civil and mining excavations has been studied, considering the effects of the generation and dissipation of NEPWP. A series of numerical simulations are conducted to determine the role of in situ stresses and time in NEPWP dissipation as well as the consequent effects on the stability of the excavated slopes. To conduct a realistic time-dependent transient analysis, fully coupled hydro-geomechanical formulation has been employed. Results show that in general, higher removal of stress levels lead to higher NEPWP generation and higher factor of safety values in the short term. Thereafter, the dissipation of NEPWP threatens the long-term stability of the excavation.
Financial support for this research has been provided by Earth Resources Regulation of the Victorian State Government Department of Economic Development, Jobs, Transport and Resources . The authors wish to acknowledge the support provided by the staff of the Yallourn Open Cut Brown Coal Mine, Energy Australia . The first author is funded by the Australian Government Research training program and Geotechnical and Hydrological Research Group (GHERG) scholarship programme at Federation University Australia . The authors are also grateful for the technical advice and assistance of Mr. Wayne Powrie (GHERG, Federation University Australia).