Study On The Deterioration Law Of Sandy Soil Surrounding Rock At Tunnel Bottom Under The Coupling Action Of Train Dynamic Load And Groundwater

In recent years,China’s heavy-haul railway transportation technology has developed rapidly,and the train speed and axle load have been increasing.The vibration and impact effects of the train dynamic load on the tunnel bottom structure gradually increase.The heavy-haul railway has the characteristics of large axle load,large total weight,high traffic density and large traffic volume,so that the rock mass at the bottom of the heavy-haul railway tunnel is subjected to greater dynamic action than that of the ordinary railway.When the heavy-load train runs in the tunnel,the vibration load generated is transmitted to the invert through the layers and produces downward instantaneous pressure on the surrounding rock at the bottom of the tunnel.The reciprocating action of the dynamic load causes a small gap between the inverted arch and the surrounding rock,and the groundwater will gradually infiltrate and fill these gaps.The reciprocating vibration of the heavy-load train will cause transient high water pressure in the underground water at the bottom of the tunnel.High-speed water will wash and erode the loose and softened particles on the surface of tunnel bottom surrounding rock,resulting in the migration and loss of particles in tunnel bottom surrounding rock,and the decrease of the physical and mechanical parameters of surrounding rock.The weakened support conditions of the tunnel bottom structure aggravate the damage,which in turn aggravate the deterioration of the surrounding rock at the tunnel bottom.The interaction between the two eventually leads to the void phenomenon of the surrounding rock at the tunnel bottom,leading to a series of tunnel bottom diseases such as mud-churning and base subsidence.At present,the problem of heavy haul railway tunnel bottom disease has been very prominent in China.In order to effectively reduce or avoid the tunnel bottom diseases of heavy-haul railway tunnels,this paper studies the deterioration law of sandy soil surrounding rock under the coupling action of train dynamic load-groundwater by means of literature research,numerical simulation and theoretical analysis,and mainly obtains the following results:1.This paper summarized the dynamic response characteristics of tunnel basement structure and surrounding rock under the dynamic load of heavy-load trains.Two deterioration mechanisms of sand liquefaction and surrounding rock particle migration and loss of sandy soil at tunnel bottom under the coupling action of train dynamic load and groundwater were analyzed.A CFD-DEM coupling analysis method for the deterioration of sandy soil surrounding rock at tunnel bottom under the coupling action of train dynamic load and groundwater was established.2.In this paper,the loss of surrounding rock particles in sandy soil at tunnel bottom under the coupling action of train dynamic load-groundwater was divided into two modes:erosion loss and seepage loss.Through literature investigation and theoretical analysis,the "initial velocity" of surrounding rock particles of sandy soil at the tunnel bottom under the action of scouring was obtained,and the corresponding calculation method of surrounding rock loss rate was established.From the microscopic point of view,the stress condition of the surrounding rock particles of sandy soil under the action of seepage was analyzed.According to the limit stress equilibrium state,the calculation formula of the critical hydraulic slope corresponding to the starting of the surrounding rock particles of sandy soil was established.The critical hydraulic slope of surrounding rock particles in sandy soil under upward seepage was analyzed,and the process of starting and losing of surrounding rock particles in sandy soil under upward seepage was simulated by using CFD-DEM coupling analysis method.3.The permeability and migration of fine particles in the surrounding rock of sandy soil under the action of seepage were analyzed.Based on the law of erosion and deposition of fine particles in the surrounding rock of sandy soil,a method for calculating the loss rate of surrounding rock under seepage was established.The established calculation method was used to analyze the rule of surrounding rock loss of sandy soil at tunnel bottom under the coupling action of train dynamic load-groundwater.By reducing the elastic reaction coefficient of surrounding rock to simulate the deterioration of surrounding rock.The influence law of the deterioration of surrounding rock on the force and safety of tunnel structure was analyzed,and the control standard of the loss rate of surrounding rock with sandy soil at tunnel bottom was put forward.