| "Dolomite sandification" is a special karst phenomenon,which is manifested as: the strength of the rock mass is reduced,and a large number of pores are formed,but the integrity of the rock mass can be maintained.After disturbance,sandified dolomite is easy to loosen and become a mixture of dolomite sand and silt.Under seepage pressure,it is prone to produce seepage deformation,resulting in water inrush and sand inrush,which poses great challenges and risks to construction.At present,there are few researches on tunnels in sandified dolomite stratum at home and abroad,especially on the catastrophic mechanism of the tunnel face.In view of the above problems,this paper relies on the Chengdu-Kunming Railway Jixin Tunnel to conduct relevant research through field investigation,indoor experiment,numerical simulation and theoretical analysis.This paper reveals the macro and micro mechanisms of dolomite sandification,obtains the influence of multiple factors on the stability of the tunnel face,including sandification degree,depth of burial,and water pressure,and ascertains the catastrophic characteristics and evolution rules of the tunnel face in the case of partial erosion of the surrounding rock in front of the tunnel.Furthermore,through the comprehensive analysis of the influence of various hazard factors and their interrelationships,the catastrophic mechanism of the tunnel face of the tunnel in the water-rich sandified dolomite stratum is formed.The research content aims to provide reference for future research.The main contents are as follows:(1)According to the site survey and sampling of the Jixin Tunnel,the mineral composition of the sample was obtained through microscope observation.The sandification level of dolomite was divided into slight,moderate,and severe according to the situation of the tunnel face.At the same time,the macroscopic characteristics and mechanism of dolomite sandification were explored.The microstructure of sandified parts was observed by scanning electron microscope experiment,and its structure and dissolution failure were analyzed,revealing the microscopic characteristics and mechanism of dolomite sandification.(2)A three-dimensional fluid-solid coupling calculation model was established to analyze the development law of plastic zone and the variation of displacement and stress in front of the tunnel face in the dolomite stratum with different sandification levels under different buried depths and water pressure.Based on this,the distribution range and migration law of the balance zone were determined,and the evolution process of the tunnel face from stability to catastrophe under the influence of multiple factors was revealed.(3)According to the particle gradation obtained by the screening test,the triaxial test conditions were designed to obtain the sandified dolomite parameters under different fine particle loss conditions.Through the establishment of a three-dimensional discrete element calculation model,the three-step method excavation simulation was carried out for each working condition.According to the analysis of the displacement of the surrounding rock in front of the tunnel face,the development model of the disturbance zone and the failure zone was obtained.Through the analysis of stress,the variation of stress in time and space is obtained.Thus,the catastrophic characteristics and evolution mechanism of the tunnel face in the case of partial erosion were formed.(4)In the end,the hazard factors of the tunnel face were described,and then the judgment matrix was constructed by the analytic hierarchy process,and their weights were calculated and compared.Through analyzing the interrelationship among four key factors,including groundwater,sandification,construction,and in-situ stress,the tunnel face disaster mechanism of the tunnel in the water-rich sandified dolomite formation was obtained,and corresponding construction suggestions were put forward based on the disaster mechanism. |
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