Effect of negative excess pore-water pressure on the stability of excavated slopes

Abstract

The generation of Negative Excess Pore-Water Pressure (NEPWP) due to the excavation of saturated soils under undrained conditions and the following dissipation of this phenomenon over time may result in different shortand 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 the excavation are lower than the ultimate equilibrium values, leading to the reduction of the average effective stresses in the slope and subsequently threatening the stability in the long term. In this research, the stability of three benchmark civil and mining excavations has been studied, considering the effects of 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, a fully-coupled hydro-geomechanical formulation has been employed. Results show that in general, higher removal of stress levels leads 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.

Study on Seepage Characteristics of Grouting Slurry for Water-Absorbing Mudstone with Rough Fissure

“…The interaction between rocks and water has always been a hot topic of research both domestically and internationally, such as the mechanical properties of water-bearing rocks [3][4][5], the water-rock coupling seepage characteristics [6,7] and the softening mechanism of rocks when encountering water [8][9][10]. Mudstone is a common special soft rock system, and has a certain water absorption ability because its mineral composition contains a large amount of clay minerals such as kaolinite, illite and montmorillonite, and due to capillary phenomenon and the presence of internal fissures in mudstone, the fissured mudstone exhibits strong water absorption [11].…”