| Karst landscapes are widely distributed in southwest China,and karst tunnels are prone to water and mud bursts during construction,which seriously threaten the safety of personnel and construction equipment.It is of great significance to investigate the characteristics of karst development and to study the influence of karst area on tunnel surrounding rocks,which are important for the research of prevention and control measures of karst tunnel sudden water disaster.This thesis takes Yiliang tunnel as the base project and analyzes the degree of influence of different control factors on the development of tunnel karst.Combining with theoretical analysis methods,the relationship equation between the safety thickness of the anti-surge rock body in front of the palm face and the cavern water pressure is derived.Based on the flow-solid coupling calculation method,numerical simulation software is used to analyze the influence law of water-rich cavern on the stability of the surrounding rock of the double-hole tunnel under different working conditions.According to the actual construction situation of Yiliang tunnel,the overrunning pipe shed support grouting parameters of the karst section of the tunnel are optimized.The main research contents and results are as follows:(1)The analysis of engineering geological characteristics of Yiliang tunnel reveals that the basic conditions for the occurrence of karst disaster in tunnel karst section are erosive groundwater,soluble rock and abundant infiltration and circulation pathways.karst development is influenced by stratigraphic lithology,geological structure and groundwater flow,which intensifies the intensity of karst development and increases the risk of tunnel sudden water disaster.(2)The karst water has a weakening effect on the anti-surge rock body,which mainly includes softening by dissolution and expansion by scouring,due to the different damage modes of the rock body when the sudden water occurs at the palm face of the tunnel,the damage of the anti-surge rock body is divided into overall tensile damage and shear damage.Rock body tensile damage is analyzed by strength theory and mutation theory,and shear damage is analyzed by strength theory considering the weakening of karst water,which simplifies the antisurge rock body in front of the tunnel palm face into elastic beam and plate mechanical model,and establishes the relationship between cavern water pressure and the safe thickness of the antisurge rock body.(3)The numerical model of fluid-solid coupling in karst tunnel excavation is established by using finite element difference software,which reveals the influence of water-bearing cavities with different locations,diameters and water pressures on the stability of the surrounding rock of the double-hole tunnel.It is concluded that the cavity located in the middle of the tunnel has a greater influence on the stability of the surrounding rock,and the risk of damage to the surrounding rock of the tunnel increases as the diameter of the cavity increases,the thickness of the anti-burst thickness decreases and the water pressure increases.By analyzing the displacement,principal stress,and plastic zone changes of surrounding rock under various working conditions,the results show that the displacement at the arch waist near the karst cave side,the principal stress at the arch foot and arch shoulder,and the plastic zone area changes of the tunnel surrounding rock are greatly affected by the karst cave.(4)For the treatment of karst geological hazards in Yiliang tunnel,the principle of combining drainage and plugging and over-support is proposed.By analyzing the advantages and disadvantages of different advanced support methods,this thesis selects advanced pipe shed support as the support method for karst sections,and optimizes the thickness of the grouting reinforcement area,and a reasonable grouting thickness of 1m was proposed. |
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