Study On Seepage State And Bearing Capacity Of Cracked Lining Under Water Pressure

As China’s infrastructure continues to improve,the existing tunnels have entered the decades-long operation and maintenance phase,and the geological conditions of the mountain tunnels are complex,which determines the high water pressure problem during both the operation and the tunnel construction period.High water pressure not only affects the traffic safety in the tunnel,but also has an adverse effect on the toughness of the lining structure,aggravating the stress distribution of the cracked lining structure,cracking,corrosion of steel reinforcement,short-circuiting of electrical equipment in the tunnel,freezing and swelling of the structure in the cold region and other problems.There is less research on the water seepage state of cracked lining structures under water pressure at home and abroad,and research in this area is urgently needed.In addition,the design parameters of the lining structure can be adjusted in time for the construction phase to prevent the effect of water pressure on the lining structure.This paper relies on the National Key Research and Development Program(2017YFC0806000)Topic 10,"Existing Urban Tunnel Damage Rapid Location and Post-Disaster Rapid Diagnosis Technologies and Equipment",and adopts theoretical analysis,numerical simulation and model test to explore the water seepage state of cracked lining structure under water pressure,and the bearing performance of water pressure at different parts of the lining structure,and discusses the water seepage assessment criteria of tunnel under water pressure at different parts.The main findings are as follows:(1)Based on similar theory,the homemade splitting small scale test block simulates the uneven and uneven cross-section of the cracked lining structure,fixed the test piece and applied water pressure by cavitation acoustic seismic test system and precision pressurized water pump respectively,explored the relationship between different crack widths and stable water pressure and the relationship between crack width and flow velocity,analyzed the relationship between water pressure and flow velocity and the relationship between water injection pressure and stable water pressure,and obtained the maximum stable water pressure that can be achieved by different crack widths and the law of flow velocity change under stable water pressure conditions.(2)The results of the model test analysis,using FLUENT numerical simulation software,perfected the conditions under which the test equipment could not be tested.Ignoring the uneven material and shape of the specimen in the model test,the Cronos high-precision scanner was used to obtain the three-dimensional coordinates of the section and only consider the form of the section of the specimen,to explore the flow rate values of 500-800 kpa for a crack width of 0.6mm,400-800 kpa for a crack width of 0.8mm and 300-800 kpa for a crack width of 1mm.Based on the above-mentioned model tests and numerical simulations,the flow velocity-hydraulic pressure relationship curves were fitted to obtain the water pressure range of the lining structure under different crack width conditions and under different seepage conditions.(3)Based on load-structure theory,using Midas GTS-NX finite element software,the lining structure model was established under Class V fenestration conditions,considering that the cracks of the lining structure are distributed at the gable top,gable shoulders,gable feet and wall corners,and the stress characteristics and safety coefficient changes of the lining structure under different water pressure are investigated.(4)According to the above laws of variation of safety coefficients of different structure locations,the water leakage assessment criteria in the Highway Tunnel Maintenance Code are supplemented by the degree of influence of water pressure on the lining structure under different conditions of water seepage at the position of the vault,shoulder,foot of the vault and corner of the wall,and the assessment criteria are refined to assess whether the existing tunnel is in a state of structural damage or water seepage affecting the traffic after the disaster.