Expansion Of Water Inrush Channel,Minimum Rock Thickness And Escape Routes Optimization Of Karst Tunnel

Water(mud)inrush is one of the main geological disasters during the karst tunnel construction.The occurrence frequency and death toll caused by water(mud)inrush are both on the top levels in serious tunnel accidents at home and abroad.So in this thesis,the expansion mechanism of water inrush channel,minimum rock thickness between excavation opening and filling-type karst cave,and escape routes optimization after water inrush from the karst tunnel are systematically investigated by theoretical analysis,numerical simulation and engineering projects.Moreover,as for the Qiyueshan karst tunnel,solute transport characteristics and groundwater connection structures of karst water tracing,risk evaluation of water and mud inrush are further researched by field tests,numerical simulation,theoretical analysis and engineering application.(1)Considering the effects of water erosion,seepage force and soil cohesion,three-dimensional force analysis for the soil particle on the side wall of water inrush channel is conducted.The critical condition for incipient particle motion is established.The incipient flow velocity for sliding instability and rolling instability of the particle is deduced respectively.The criterion of incipient particle motion is proposed.The expansion mechanism of water inrush channel is revealed.The influencing factors of the incipient flow velocity are analyzed and the rules of particle loss are discussed.Finally,through the analysis of particle-fluid coupling and calculation of DEM-CFD coupling,numerical simulation for the incipient particle motion and channel expansion is implemented,and the proposed mechanism of incipient particle motion is verified.(2)Four typical karst cave locations(i.e.,at the top,bottom,lateral and front of the tunnel),two types of filled karst caves,with water and with water-mud mixture,are studied,to estimate the required thickness of supporting rock stratum in order to prevent water and mud inrush under earthquake conditions.Generalized models and computational techniques are developed for such conditions.The models consider the shear,bending and punching failures of the supporting rock stratum against the pressure from filling materials in the karst caves.Combined with quasi-static and dynamic theories,computational models are developed to estimate the minimum safety thickness of the rock stratum between the excavation opening and the filling-type karst cave.The factors governing the minimum safety thickness of the supporting rock stratum to resist water and mud inrush from the karst caves are analyzed.Finally,the theoretical models and computational methods are verified with case studies.(3)Numerical simulation of the gas-liquid two-phase flow is carried out by using the FLUENT software to probe water flow characteristics after water inrush.Eight common cases of water inrush from the working face and the floor during double-line tunnel excavation are researched.The variation rules of velocity,pressure and water volume fraction in the tunnels after water inrush are analyzed.The optimized escape routine is respectively formulated for the eight water inrush cases.The water movement laws under the conditions of different excavation situations and different water inrush positions are further discussed by comparing the above case studies.(4)The solute transport characteristics and groundwater connection structures of karst water tracing are studied by numerical simulation and field tracer tests.The simulation method of solute transport is first proposed.Then five kinds of representative geological models of karst water tracing are built,and the process of solute transport is simulated in the FLUENT software.The variation characteristics of solute transport under the conditions of straight pipeline,bend,depression,waterfall and branch pipeline are analyzed based on the simulation results.The effects of the pipeline width.flow velocity,size of the bend,depression depth,the number of bends,depressions and waterfalls,and path difference of the branch pipeline on the tracer curve are discussed.General laws of groundwater connection tracer curve are summarized.Finally,according to field test results,the groundwater connection structures are analyzed and speculated in detail by the flow velocity and local monitoring curve.(5)In order to effectively control the water and mud inrush risk and guarantee the safety of tunnel construction,an unascertained measure model of water and mud inrush risk evaluation is established based on the unascertained measure theory.First,according to geological factors and engineering factors in tunnel zone,unfavorable geology,formation lithology,ground water level,topography and geomorphology,attitude of rocks,contact zones between soluble rock and non-soluble rock,crack in rock stratum,surrounding rock grade,construction technology level,and management level are selected as risk evaluation indexes of water and mud inrush,which constitutes the index system of water and mud inrush risk evaluation.Through collecting and collating information of typical water and mud inrush examples of karst tunnels,the uncertainty measure function of each evaluation index is obtained based on the measured data.Meanwhile,the index weight of each factor is ascertained by the entropy-information theory,and the risk grade of water and mud inrush is judged by the credible degree recognition criteria.In engineering application,the water and mud inrush risk of the Qiyueshan karst tunnel is evaluated based on the established unascertained measure model.