Generalized modes and academic criterions of water inrush from paleo-sinkholes

According to locational relations between a paleo-sinkhole and a working face or tunnel, the modes of paleo-sinkhole-caused water inrush (hereinafter referred to as water inrush from paleo-sinkholes) are divided into the mode of water inrush from roof/floor and the mode from rib as well as four sub-modes, including the thin plate sub-mode of water inrush, the shear failure sub-mode, the thick wall cylinder submode and the hydro-fracture sub-mode. The thin plate sub-mode is applicable to the circumstance where the key layer of cylinder cover is complete and has small thickness, and its criterion of water inrush is the limit bending moment. The shear failure sub-mode is applicable to the circumstance where the key layer of cylinder cover has big thickness, and its criterion of water inrush is a quadratic parabola equation. In the thick wall cylinder water inrush mode, the elastic limit pressures that may lead to failure of the thick wall cylinder are different as the different yield empirical rules, but all are in direct proportion with the strength of rock stratum. The hydro-fracture sub-mode of water inrush describes the type of water inrush that occurs due to the interconnection between underground water and other inherent structures through hydro-fracture when the paleo-sinkhole is far from the working face or tunnel. The critical hydro-fracture pressure may be calculated by reference to the formula used for calculating hydro-fracture. It is indicated by an actual example that the water inrush modes and their criteria are simple and feasible, conform to the realities and have sufficient accuracy.