Study On Seepage Chracteristics With Mass Loss Of Broken Rock In Mountaintunnel Containing Fault

With the rapid development of our country’s infrastructure,a large number of high-risk tunnels are to be built,and these tunnels have the remarkable characteristics of long tunnel length,high stress,high water pressure and complicated geological structure.Water inrush from fault fractured zone is a major geological hazard occurring at high frequency in the process of tunnel construction.It has great influence on tunnel construction safety,once disaster occurs,it will cause delay in construction period and even endanger the safety of construction personnel.The essence of water inrush in fault fracture zone is the variable mass seepage problem of fractured rock mass,Therefore,the study of the variable mass percolation behavior of the fractured rock is of great practical significance for the prevention and control water inrush accident in the fault zone.In this paper,the key factors inducing water inrush from the fault are determined by analytic hierarchy process(AHP),the fractured rock mass of fault was taken as the research object,this paper studies a series of research on the multi parameter response to the full water condition,the filling particle size distribution,fault structure,fault depth exposed by the tunnel based on the combination of model test and numerical simulation,some research results have been achieved through the relevant research and play a positive role in guiding engineering practice.(1)There are lots of influencing factors water inrush from fault,in this paper,the main influencing factors are analyzed and classied.A hierarchical structure model of the influencing factors of the water inrush was set up and the judgement matrix was constructed based on the basic principle of analytic hierarchy process(AHP),The importance degree of the factors was calculated and the consistency check was carried out.Finally,the key factors inducing water inrush from the fault were determined.(2)Independently developed a visualized model test device for variable-mass percolation in fractured rock mass,including a water supply device,an acrylic glass tube receiving device,a water inrush collection device and a support.With this device,a seepage model test was conducted using the particle size distribution(continuous gradation,missing gradation),water-rich conditions,and gradation of engineering examples as the research variables,described and analyzed the variable mass loss phenomenon of various experiments during the multi-parameter response,obtained the key parameters describing the variable mass flow,such as the composition structure of lost mass,the time-varying law of lost mass,the time of water inrush,and the amount of settlement,summarized the variable mass flow characteristics of different sample structures.(3)A multi-physics simulation software COMSOL Multiphysics was used to establish a seepage model based on the coupling of Darcy’s law and PDE.Numerical calculations were conducted using water pressure and initial porosity as research variables,the dynamic changes of porosity and permeability in the model were obtained.The time demarcation point of the change of seepage state is analyzed.This point is also the demarcation point of the change of seepage parameter.The numerical simulation results are compared with experimental research results,and the rationality of the experimental research and numerical simulation research was verified.(4)A variable mass flow seepage model for faults in tunnels was established based on the Darcy-Brinkman-Navier-Stokes equations.The numerical calculations of the study variables were carried out in terms of water-rich conditions(water pressure,location of confined water layer),fault fracture zone(fault zone width,dip,and permeability),and tunnel exposure depth.Numerical simulations have obtained the characteristics of flow velocity and distribution of flow lines in different flow fields,the variation law of flow velocity on the axis,the characteristics of water pressure changes in different regions,and the law of changes in water pressure on the axis,which provide a useful reference for revealing the macroscopic features of the flow fields in the process of fault water inrush.(5)Based on the results of model tests and numerical simulations,the effects of fault filler particles(dominated by the fine-grained group,dominated by the homogeneous-grained group,dominated by the coarse-grained group),and the water-rich conditions(velocity,water pressure)on variable mass flow characteristics were summarized,reveals the variable mass seepage of the broken rock mass of the water-rich fault.