Research On Water Pressure Distribution Pattern Of Mountain Tunnel Based On The Physical Simulation

As a nonnegligible key factor in the analysis of mountain tunnels’ construction,the external hydraulic pressure can have a critical influence on the tunnel siting scheme or its own design scheme.Because of the difficulty of monitoring external hydraulic pressure and the lack of external hydraulic pressure calculating method of tunnel based on the engineering verifications,the estimation of external water pressure mainly relies on experience to reduce hydrostatic pressure or adopt pure theoretical formulas,so estimating value and actual value often differs very far.Consequently,based on the brief discussion and summarization of theoretical foundation that can be used to simplify and analyze mountain tunnels physical simulation experiment-Theoretical system of seepage model for equivalent continuous medium of groundwater,the paper focuses on analyzing and discussing the application conditions of the groundwater equivalent continuous medium seepage model in fractured rock mass: The Rev value exists and the sample size is not smaller than the Rev value and the seepage is stable.Then,based on the analysis and summarization of the previous relevant research results andthrough the argument by example and the contrast argument,the analysis obtains thathydrogeological structure and boundary conditions included in hydrogeological dominating key factors of seepage in the tunnel area has dominant function over the external hydraulic pressure of the tunnel.And finally,taking a tunnel respectively lying in equal head at both sides of the tunnel axis with homogeneous rock mass hydrogeological dominating key factors(A1)and equal head at both sides of the tunnel axis with near horizontal homogeneous layered hydrogeological dominating key factors(B1)as the study object,the paper concludes that the distribution regularity of the external water pressure under the condition of the full drainage tunnel without lining,no drainage with full blocking and the lining with blocking and drainage as followed through the approximate equivalent static mechanics physical simulation experiments.1 Under the condition of full drainage tunnel without lining,no matter which of the two types of hydrogeological dominating key factorsthe tunnel lies in,the near field external water pressure has a greater reduction in the hydrostatic pressure of the corresponding depth in relation to the boundary head.However,the corresponding problem is excessive quantity of water gushing,which is prone to ecological and environmental geological problems in the longer term,and the smaller the overall permeability of surrounding rocks is under the same boundary water level,the greater the external hydraulic pressure of tunnel near-field is.2 No matter tunnel lies in A1 type of hydrogeological dominating key factors or in B1 type of hydrogeological dominating key factors,because the form characteristic of water level above the tunnel is influenced greatly by the permeability of rock mass surrounding the tunnel,which is not easy to form a near horizontal water level.Thus under the condition of full drainage tunnel without lining,only under the circumstance of low-permeability surrounding rock mass could Axisymmetric Analytic method be suitable for estimating the piezometric head of the lining.3 Under the condition of no drainage with full blocking,the external hydraulic pressure value of the tunnel is the hydrostatic pressure value of its corresponding position,which relates only to the buried depth of the tunnel.4 When taking measures of lining with blocking and drainage to tunnel,no matter tunnel lies in A1 typeof hydrogeological dominating key factors or in B1 type of hydrogeological dominating key factors,piezometric heads at any point of the lining surface in the same working condition are all approximately equal to each other and its reduction degree is less than that of the same position under the same working condition except without lining.5 Under the condition of lining with blocking and drainage,using Axisymmetric Analytic method to estimate the piezometric head of tunnel lining surface when the the tunnel lies in A1 type of hydrogeological dominating key factors,the estimation values are smaller than the measured values and the errors are not more than 2% if the boundary water level is not more than 114 m high in relation to the center of the tunnel and the permeability of the lining is not more than 0.008m/d.6 Under the condition of lining with blocking and drainage,based on conclusions above and combining the data of working condition,the hypothesis and comparative analysis methods are used to know that Axisymmetric Analytic method could be adopted to estimate the piezometric head on the lining surface of the tunneland thekw could be taken as the permeability coefficient of permeability media at the bottm when tunnel lies in B1 type of hydrogeological dominating key factors and in permeability media at the bottom.