| With the development of national infrastructure construction and the in-depth implementation of "Road and Belt" strategy,China’s transportation,hydropower and other major engineering construction focus is shifting to the western mountainous and karst areas with extremely complicated topography and geology.These tunnel projects are generally characterized by large buried depth,long tunnel line and complex hydrogeological conditions,which lead to many geological disasters in tunnel construction,among which water inrush and mud inrush is one of the main geological disasters in tunnel construction.In this paper,based on Chengdu-Lanzhou railway tunnel project,indepth study on the water inrush mechanism and risk control were carried out,by theoretical analysis,numerical simulation,laboratory experiment,software development and field test.Some research results of important theoretical value and project significance were summarized,listed as follows:(1)Based on the failure and instability types of filling medium,the seepage model and mechanical model of different failure modes were put forward and the development process of seepage failure were revealed.For permeable failure,seepage erosion model was established,the relationship of flow velocity in seepage channel was derived,considering the seepage channel flow characteristics and the stress of the soil particle moving characteristics,the critical hydraulic gradient calculation methods of contact erosion were proposed.For sliding failure,the instability criterion and minimum safe thickness criterion based on strength condition were proposed,The influence of different factors on critical length was analyzed(2)According to the case of water inrush and mud gush in Yangjiaping tunnel,similar materials of filling medium were prepared,seepage instability test were carried out by using 3D model test system and the whole process of water inrush and mud inrush induced by filling medium seepage instability were simulated.By analyzing the water inflow content,particle loss content,porosity and permeability evolution characteristics,the influence of clay content and seepage loading rate on the seepage instability process of filling medium structure were studied.The whole seepage process was divided into three stages:initial seepage stage,accelerated seepage stage and stable seepage stage,the seepage characteristics of each stage were described in detail.The grain size distribution and basic mechanical parameters of different parts of filling medium before and after seepage test were compared and analyzed,which revealed the progressive evolution law of seepage instability of filling medium structure.(3)Based on the basic principle of discrete element method,combined with the microstructure and cementation characteristics of filling medium,a variable bond strength model of filling medium was proposed.Through numerical simulation,the variation law of particle displacement field and contact strength between particles in the process of direct shear test was revealed.The influences of contact stiffness,bond radius,unit bond strength and particle friction coefficient on the macroscopic parameters of shear strength,cohesion and internal friction angle of filling medium were analyzed.The bond weaken criterion considering hydraulic erosion was also proposed.Finally,a simulation analysis method for fluid-solid coupling in twophase media was developed based on DEM-CFD method.By conducting filling medium seepage numerical simulation test,the flow field,porosity,particle loss,erosion rate and particle force variation under different clay content and seepage loading rate were studied,and the seepage instability evolution process of filling medium were simulated,which providing a numerical simulation method for the water inrush evolution process of tunnel filling disaster induced structure.(4)Based on the geological survey information,conventional advanced prediction,tunnel induced polarization method,targeted boreholes,combined with real-time dynamic information of tunnel construction,"Two-stage" comprehensive assessment method for tunnel water inrush disaster was put forward.According to the different evaluation results of different stages,the dynamic control and construction decision scheme to deal with water inrush disaster were proposed.Then the risk assessment method of tunnel water inrush was integrated with corresponding control measures,and the software of tunnel water inrush disaster assessment system was developed.Relevant research results have been successfully applied in the highrisk water inrush section of Yuelongmen tunnel in chengdu-Lanzhou Railway. |
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