| With the rapid development of high-speed railway construction,high-speed trains put forward higher requirements for track smoothness.Due to the influence of complex factors such as lithology,geological structure and groundwater,the high-speed railway tunnel built in the western mountainous area of China often has the problem of tunnel inverted arch uplift.The elevation of tunnel inverted arch will directly affect the smoothness of high-speed railway track,and even affect the driving safety of high-speed railway trains in serious cases.Therefore,it has important engineering application value to study the mechanism of inverted arch uplift in complex mountain tunnel.Based on the background of the high-speed railway project under construction in Chongqing,on the basis of comprehensive analysis of engineering geological conditions such as stratum lithology and geological structure along the railway line,the factors affecting the uplift of tunnel inverted arch are systematically studied by means of laboratory test and numerical simulation.The main research contents and results are as follows :(1)Through the analysis of the engineering examples of the inverted arch deformation of 15 tunnels,it is concluded that the main reasons affecting the uplift of the tunnel inverted arch include groundwater,surrounding rock expansion,ground stress and construction quality problems.The tunnel area with inverted arch uplift is characterized by mudstone,shale,argillaceous sandstone and other soft rocks.(2)The uplift types of inverted arch at the bottom of the tunnel are summarized and classified.According to the different geological environments(surrounding rock properties,geological conditions,and stress states),they are mainly divided into extrusion flow type,water swelling type,shear dislocation type,and flexure fold type.Based on the strength deterioration theory of surrounding rock,the deterioration process of surrounding rock and the evolution law of tunnel inverted arch are discussed and analyzed.(3)The expansion rate of 32 rock samples in the engineering area was tested,and six expansion force tests were carried out.The maximum limit expansion rate was 2.29 %,and the maximum expansion force was 1.3 MPa.On this basis,combined with wave velocity test,the exponential function relationship between expansion rate and wave velocity is established.Based on the disintegration test,the fracture development of mudstone after encountering water was studied,and the time-history curve of rock disintegration and the change relationship of fracture width were analyzed.(4)The orthogonal experiment is designed,and the numerical simulation method is used to study the influence of groundwater,ground stress,expansion force and the thickness of mudstone at the bottom of the tunnel on the uplift of the tunnel.From large to small,the influence is ground stress,expansion force,groundwater and the thickness of mudstone at the bottom of the tunnel.(5)Numerical simulation and theoretical study show that the degradation of groundwater is closely related to time.When the surrounding rock strength of the tunnel affected by groundwater decreases by 20 % ～ 30 %,the uplift of the inverted arch will increase rapidly;when the degradation range of tunnel surrounding rock increases to 3 times the hole diameter,the amount of inverted arch lifting increases rapidly,and the increase of inverted arch lifting is not obvious at 3-5 times the hole diameter.(6)Taking the inverted arch lifting disease of a tunnel in Chongqing as an example,a comprehensive study was carried out combined with field data,test results,theoretical analysis and numerical simulation methods.The results show that in the process of tunnel excavation,due to the combined action of multiple factors such as geostress and low surrounding rock strength,the load borne by the tunnel lining is increased,resulting in the cracking of the tunnel top and the uplift of the inverted arch. |
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