Research On Seepage Instability Mechanism And Application Of Water-Rich Fault Zone Under Excavation Disturbance-Seepage Coupling

The problem of seepage instability caused by the exposure of fault structural zones in underground engineering construction is an urgent problem to be solved.The expansion and failure of surrounding rock fractures caused by the change of hydraulic conditions and seepage state of water-rich fault zones under excavation disturbance is one of the key factors causing seepage instability.Existing studies have not coupled excavation disturbance and seepage,and have not revealed its inherent correlation and driving seepage instability characteristics from the mechanism.It is difficult to accurately describe the change process of excavation face and the deformation characteristics of rock mass in waterrich fault structural zone.In view of this,this dissertation takes the seepage instability disaster of water-rich fault as the research object.Through theoretical analysis,laboratory test and case analysis,it focuses on the seepage instability mechanism of crack propagation-through of rock mass in water-rich fault structural belt under excavation disturbance and seepage coupling,clarifies the formation process of dominant water inrush channel of seepage instability,and establishes the calculation model of safe rock wall thickness of crack propagation-seepage instability of rock mass under hydraulic fracturing.The applicability of the calculation model is verified by engineering cases.The main research contents and results of this dissertation are as follows:(1)Based on the comprehensive geological analysis of the development characteristics of the water-rich fault structural zone,the seepage instability disaster conditions of the water-rich fault structural zone are systematically summarized.It is considered that the main influencing factors of the seepage instability disaster of the water-rich fault structural zone are the change of the surrounding rock seepage conditions and the disturbance of the engineering excavation.The comprehensive identification and early warning system of the seepage instability disaster of the water-rich fault is established.Finally,the engineering example verifies that the identification system can better predict the precursor information of the fault seepage instability.(2)According to the engineering case analysis of seepage instability of water-rich fault,the indoor compression test of sandstone with prefabricated cracks under the coupling effect of dynamic load and seepage is further carried out.The initiation,coalescence and failure process of rock cracks under four loading forms of high and low strain rate loading,conventional loading,dynamic and static combination loading and loading and unloading are studied.The results show that the water wedge effect of high-water pressure on rock mass under dynamic load is the dominant factor causing seepage instability.Based on the whole process acoustic emission time domain and frequency domain parameters,the influence of dynamic load frequency amplitude and osmotic pressure on crack failure mode,stress intensity and seepage law are analyzed,and four critical stress calculation models during crack development are established.(3)According to the laboratory test results of rock mass crack penetration instability under seepage state,it is considered that the seepage instability of water-rich fault is caused by rock mass fracture instability under hydraulic fracturing.The stability state of water-rich fault fracture zone is studied by using friction coefficient method and in-situ stress test method.The initial damage theory and silo theory are further introduced to comprehensively analyze the seepage instability process of rock mass under excavation disturbance.The swallowtail catastrophe model of seepage instability of water-rich fault under initial damage-disturbanceseepage coupling is constructed.The judgment criterion and calculation parameters of critical state of seepage instability are proposed.The calculation formula of critical velocity is established when laminar flow changes into turbulent flow.(4)Based on the analysis of the role of the safety rock wall in the rock mass in front of the excavation,the whole safety rock wall is divided into three parts: the water-rich area,the main water-resisting area and the excavation disturbance area according to the seepage instability.Firstly,the critical water pressure of rock mass subjected to compression-shear or tension-shear failure under hydraulic fracturing is analyzed,and the calculation formula of rock mass thickness in the main water-resisting zone during crack coalescence failure is proposed.Secondly,the excavation disturbance load and seepage state parameters are introduced,and the catastrophe theoretical calculation model of rock wall thickness in excavation disturbance area under disturbance load-seepage coupling is established.(5)A similar material model test of fault seepage instability in a project is carried out.Combined with the water diversion loading platform and the stress control monitoring system,the influence of excavation disturbance and water seepage coupling on the water-rich fault fracture zone during the near-fault excavation of the project is simulated.The variation laws of fault displacement,stress and water flow in the excavation process are mainly studied.The test value and field engineering experience value of safety rock wall thickness are compared when the stress and hydraulic state changed suddenly,and the rationality and engineering applicability of the safety rock wall thickness calculation theory are verified.(6)Based on the analysis of the comprehensive identification and early warning method of fault seepage instability disaster,the control measures of seepage instability of water-rich fault considering the thickness of safety rock wall are proposed.Combined with the calculation and analysis results of the safe rock wall thickness in the water-rich fault structural zone of a high-speed railway tunnel project,the supplementary risk assessment of the excavation and excavation of the water-rich fault structural zone is carried out,and the preset seepage instability control measures are strengthened.The whole water pressure monitoring and well point dewatering test applied to the seepage instability of the water-rich fault in the tunnel are proposed,which effectively ensures the safe and smooth excavation process through the water-rich fault zone.