Research On Mechanical Properties And Stability Of Long-term Waterlogged Surrounding Rocks In Karst Tunnels After Water Gushed

In southwest China,the problem of karst water gushing in the tunnel construction process is prominent and has become a major problem in tunnel construction.This thesis takes the long-term water treatment program after karst water gushing in the Yingpan Mountain tunnel counter-slope slope work area of Huali Expressway as the engineering background,and uses data research,theoretical analysis,indoor test and numerical analysis to conduct an in-depth study on the mechanical properties of surrounding rocks after water gushing in extra-long water-rich karst tunnel and the change law of tunnel surrounding rock stability.The research contents and results mainly include.(1)Comprehensive research at home and abroad in water-rich karst areas of groundwater endowment characteristics and groundwater circulation characteristics,combined with this relying on the project karst lot groundwater development characteristics,inductive analysis of the Yingpan Mountain tunnel karst lot groundwater endowment characteristics,combined with Yingpan Mountain tunnel geology,hydrology and surge characteristics,the Yingpan Mountain tunnel surge water risk evaluation,the risk of each surge water-causing factors are ranked as follows: width of the fracture zone > pressure water pressure conditions > fold structure morphology > support measures > tunnel depth > diving groundwater level > construction disturbance > precipitation > joint fissure > tunnel length >temperature.(2)Indoor tests of physical and mechanical properties of surrounding rocks under different immersion lengths were completed,and physical and mechanical parameters(density,water content,permeability coefficient,compressive strength)and change laws of surrounding rocks under different immersion lengths were obtained,and the results showed that: the natural density and dry density of dolomite are greater than those of chert;the saturated water content of dolomite is much lower than that of chert;when the surrounding pressure is the same,the longer the immersion time of the specimen,the lower the peak The longer the specimen is immersed in water,the lower the peak compressive strength.The cohesion and internal friction angle of dolomite and chert generally show a decreasing trend with the increase of water immersion time.In addition,the effect of water immersion time on the physical and mechanical properties of the specimens was not equivalent,and the effect of water immersion time on the mechanical properties of the rocks was more persistent.(3)For the problem of the low success rate of core making for dolomite with jointed fracture development,we propose a method to prepare specimens for dolomite infiltration reinforcement using an acrylic resin in acetone to make samples and recover the mechanical parameters of rock samples upon successful sample preparation.Several groups tested by the optimized ratio of acrylic resin and acetone revealed an optimized solution mass fraction of 20% had the best effect on fractured dolomite reinforcement in the sampling location and increased the success rate of rock preparation from 15% to 54%.The physical and mechanical properties of the specimens were unaffected after immersion in pure acetone for 48 h.(4)Based on the longitudinal displacement mutation principle and the cusp mutation criterion,the minimum safety rock column thickness for different tunnel depths and different cavern water pressures of deeply buried high hydraulic pressure karst tunnels is determined by using theoretical and numerical analysis methods in conjunction with the dependent projects,and the minimum safety rock column thicknesses are obtained for cavern water pressure of 2MPa,2.5MPa,3MPa,and palm face displacement mutation at burial depths of 300 m,600m,and 900 m.The results show that the safety column thickness increases with the increase of cavern water pressure and tunnel burial depth,which provides technical support for the determination of the cavern treatment range.(5)Through numerical simulation analysis of the tunnel after the water surge surrounding rock stress evolution and stability law,based on the distribution of the plastic zone around the cave rock,stress and displacement change characteristics and combined with different burial depth of the tunnel,different cavern water pressure analysis of the tunnel surrounding rock stability change law,the results show that: the tunnel burial depths on the plastic strain effect is higher than the cavern water pressure;tunnel forward direction of the rock column by the tensile stress is funnel-shaped distribution,stress The value decreases from the palm surface to the forward direction;the horizontal displacement values of the tunnel arch settlement and the arch bottom rise and the tunnel arch waist area increase with the increase of tunnel depth and cavern water pressure.The results of the study guide determining the engineering treatment measures for the waterlogged section of the karst tunnel to ensure safe construction.