Experiment And Mechanism Study On Stress-seepage Evolution In Rock Mass Rupture During Water Inrush In Tunnels

With the rapid development of the national economy,now China is the country with the fastest,largest scale and most difficult tunnel construction globally.In order to optimize the national transportation network and maintain national security and unity,with the advancement of the "Sichuan-Tibet Railway" and "One Belt One Road"strategy,southwest mountainous areas and strong karst areas with extremely complex geological conditions have gradually become the focus of national major projects These tunnel projects generally have significant characteristics such as large buried depth,long tunnel line,and complex hydrogeological condition.In the geological survey stage,it is often difficult to conduct detailed and accurate exploration of the geological conditions along the tunnel.This shortage greatly increases the risk of major disasters such as water and mud inrush during the tunnel construction period,and unexpected water inrush disaster becomes a key factor affecting construction safety and costs.The excavation disturbance and high seepage pressure caused the damage of surrounding rock,and following seepage catastrophe is important reasons for the tunnel water inrush.This dissertation focuses on the water inrush disasters that severely restrict the construction of deep and long tunnels,comprehensively adopts theoretical research,numerical simulation,indoor experiment and model test and other methods to study the scientific problem that disaster prevention and mitigation of water inrush in tunnels.Research on the stress-seepage evolution mechanism of rock mass rupture during water inrush in tunnels has achieved the following research results:(1)The stress characteristics of water-resisting rock mass under construction disturbance are analyzed,and the "three zones" division method of water-resisting rock mass based on the stress field’s evolution is proposed.The stress-seepage coupling test of water-resisting rock mass under the loading and unloading stress path is carried out based on the MTS system.The influence of loading and unloading rates on the rock mass’s strength and deformation characteristics is also analyzed,and the characteristic stresses during the progressive failure of the rock mass are determined as well.The energy evolution in the process of progressive failure of rock mass and the correlation characteristics of rock deformation and permeability evolution are studied,and the creep fracture mechanism of rock mass failure under high seepage pressure is revealed.It is believed that high seepage pressure is an important point causing the rock mass failure.(2)A novel experimental method for stimulating fractured rock masses with high-pressure fluid is proposed.Shear-flow tests with a single fracture under hydraulic-mechanical coupling are carried out,and the permeability evolution before and after shear slip under different confining pressures is obtained.The fracture permeability is jointly affected by fracture roughness,effective stress,and shear displacement.The linkage evolution mechanism of high effective stress,shear displacement and fracture permeability under confining pressure is analyzed.The greater the effective stress,the smaller the fracture permeability is.When the effective stress is constant,there is a critical threshold of shear displacement that affects the permeability change.A model for the permeability evolution of a single-fractured rock mass under the action of shear displacement is proposed,which reveals the permeability evolution of the single-fractured rock mass under the action of shear displacement.(3)Based on the three-dimensional fluid-solid coupling similarity theory,the fluid-solid coupling similar materials that meet the rock masses’ hydraulic and physical properties are developed.An innovative high water pressure loading and sealing technology are proposed.A test system that can simulate seepage changes in tunnel excavation under complex geological conditions is developed and produced.Two different model tests to research the seepage failure of rock mass during water inrush in the tunne!are carried out by combining the mentioned similar material and model system.The distribution of the seepage field of the rock mass under different seepage pressures is studied,and the stress-seepage evolution trend in the water inrush disaster of the water-insulating rock mass rupture is obtained.The stress-seepage evolution of water-resisting rock mass during tunnel excavation is revealed.(4)The structure of water-resisting rock mass and corresponding water inrush failure types are analyzed systematically,and the theoretical analysis of rock mass stress-damage-seepage interaction is carried out.The porosity is used to characterize the damage of the rock mass,and the permeability evolution with the damage variables during the progressive failure of the rock mass is analyzed.The hydraulic fracturing characteristics of single and multiple cracks and the critical water pressure are studied based on fracture mechanics.The influence of the stress coefficient and the crack inclination angle on the critical water pressure are studied,and the water-resisting rock mass’s stress evolution characteristics during the construction process are studied based on numerical simulation.The influence of excavation disturbance and high seepage pressure on the resisting ability of rock mass is analyzed.The seepage failure mechanism of water-resisting rock mass during water inrush caused by excavation disturbance and high seepage pressure is also revealed.This dissertation ’s research results are beneficial to enrich the theoretical system of tunnel water inrush disaster and provide scientific basis and academic support for the prevention and mitigation of water inrush and mud in tunnel engineering.