Study On Prediction Method Of Grouting Water Blocking Effect In High Water Pressure Mountain Tunnel

The grouting and plugging of water is a common measure to prevent and control the flooding of mountain tunnels.The effect of plugging water is very important to the construction and operation safety of high water pressure tunnels.In order to understand accurately the water inrush state of tunnel construction environment after grouting,and to guide grouting construction and tunnel drainage system design in theory,this paper deduces the permeability coefficient formula of rock mass in grouting area and replaces the inrush water quantity estimation model through theoretical analysis.The calculation of the effect of grouting and plugging in high water pressure tunnel is realized,and the feasibility of the model is verified by the case of water grouting prevention and control in water rich area.At the same time,considering the change of seepage force,the change of permeability coefficient of surrounding rock after excavation of high pressure tunnel is analyzed and studied.Numerical simulation software is used to establish the calculation conditions,and the influence of the setting parameters of the grouting ring on the seepage flow field and the effect of grouting blocking water in the tunnel is analyzed.The main research work and conclusions are as follows:（1）Study on Permeability Coefficient Distribution Law of Surrounding Rock Considering Variation of Seepage Water Pressure.Based on the theory of groundwater dynamics,the calculation formula of groundwater seepage pressure is deduced,and its application feasibility is verified by Flac^3D.The expression of surrounding rock permeability coefficient considering the influence of seepage water pressure is obtained,and the coupling variation characteristics of rock mass permeability coefficient are analyzed by an example.The calculation of permeability coefficient of surrounding rock of high water pressure tunnel should consider not only the coupling effect of stress field and seepage field in surrounding rock,but also the change of fracture state and seepage force as influencing factors.（2）Analysis of water reducing effect of grouting in high water pressure tunnel.Flac³DD is used to study the variation of seepage field and water inflow in tunnel surrounding rock under different grouting circle thickness and permeability coefficient.Considering the economic factors,when the permeability coefficient of grouting ring is constant,the thickness of grouting ring is not the bigger the better,but there is an optimal thickness of grouting ring.When the thickness is bigger than this value,the effect of increasing thickness on the improvement of seepage field and water plugging effect of surrounding rock is not obvious.If the thickness of grouting ring is assumed to be unchanged,the smaller the permeability coefficient of grouting ring is,the more obvious the improvement effect of grouting on seepage field and water plugging effect of tunnel surrounding rock is.（3）Study on prediction model of grouting water shutoff in high water pressure tunnel.On the basis of basic assumptions,a simplified fracture calculation model around grouting hole is established,and the variation law of porosity in grouting area before and after grouting is analyzed.Based on cubic law,the formula for calculating permeability coefficient of surrounding rock after grouting is deduced.The surrounding rock of tunnel is simplified as an ideal equivalent continuum medium model,and the prediction model of grouting water plugging effect is deduced by using groundwater seepage theory.The model can be used for preliminary calculation and prediction of water shutoff effect of grouting.（4）Engineering feasibility verification of grouting water shutoff prediction model.Based on the engineering geological data and the summary report of water inrush and breakage section of Tiefengshan No.2 tunnel,the relevant calculation parameters and grouting parameters of tunnel surrounding rock are summarized and selected.Taking the change values of water inrush before and after grouting as the research object,the change values of water inrush calculated by the model and the measured water inrush before and after grouting are compared and analyzed,and the high-pressure tunnel is verified.The engineering feasibility of the prediction model of grouting water shutoff.