Research on safety thickness to resist basal inrush failure in rock ground excavations subjected to a confined aquifer
The water inrush or instability failure at the deep excavation base is a common engineering disaster subjected to the action of lower confined water.In order to ensure the basal safety in deep excavations,setting enough safety thickness is the key to prevent such failure.Based on the plastic upper-bound analysis theory,the basal failure range was classified into upper passive zone and lower shear zone in this paper,and a basal inrush failure mechanism for excavations in rock ground was constructed.Then,based on the Hoek-Brown strength criterion,the analytical solutions for the basal failure surface equation,critical safety thickness and critical confined water pressure were derived.On this basis,the influence laws of passive-zone thickness,confined water pressure,rock-mass parameters and other factors on the basal safety thickness and failure range were obtained,and the validity of the proposed method was verified through a comparison with the existing research works and numerical simulation results.The research shows that the critical safety thickness is positively correlated with confined water pressures and rock empirical parameter,and negatively correlated with passive-zone thicknesses,rock empirical parameter,rock compressive strength,rock tensile strength and unit weight.
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