Study On Structural Response Characteristics Of Karst Tunnel With Heavy Rainfall Condition

With the rapid development of tunnel construction in China,there are more and more existing tunnels in karst areas.During tunnel operation,it will be affected by surface rainfall infiltration and groundwater seepage,and a large amount of karst water will converge behind the lining in a short time to form high water pressure.It will cause various water disasters,affecting the safety and service life of the lining structure.This thesis mainly combined some actual cases of lining water pressure disease of domestic main high water pressure karst tunnels,summarized three types of generalized models of karst tunnels,and sorts out various factors affecting lining water pressure.Based on the engineering example of Gao Jia Ping Tunnel of Zheng Wan High-speed Railway,using numerical analysis methods,The thesis mainly studied the influence of rainfall on the distribution characteristics of water pressure in the lining of karst tunnels,and probes into the changes of internal force of the lining structure under the pipe cavity mode.The main research contents and achievements were as follows:(1)Based on the karst development characteristics and disease characteristics of existing tunnels,the karst morphology prone to water pressure disease in karst tunnels during operation is summarized and classified,and the tunnel karst system is generalized into three models: homogeneous seepage model,local pipe cavity model and fracture conduction model.The main factors influencing tunnel water pressure are lining waterproof and drainage design mode and geological factors.(2)Based on three types of generalized models of karst system,a threedimensional seepage model of tunnel was established to explore the influence of different drainage conditions,different rainfall intensities on the distribution law of lining water pressure.The results show that when it rains,the tunnel arch is the most sensitive to the rainfall factor.When the tunnel drainage failure occurred,the water pressure at each position of the lining arch wall will increase after 72 hours of rainfall,and the water pressure at the arch wall will increase the most;The water pressure of the lining arch wall increases significantly with the increase of rainfall.When the drainage failure occurs,the water pressure at the arch wall of the lining is much greater than that at the rainfall of 50 mm/d 72 hours after the rainfall of 300 mm/d,and the increase of water pressure at the arch wall is the largest,22.6%.(3)When the tunnel is drained normally,Normal drainage can effectively reduce the lining water pressure.After the rainfall of 50 mm/d reaches 72 hours,the water pressure at the middle corner of the lining arch wall will be reduced by the largest amount,with a water pressure reduction rate of about 0.9.The water pressure at the inverted arch will be reduced by the smallest amount,with a water pressure reduction rate of about 0.1.(4)Established a three-dimensional tunnel load structure model to further explore the influence of different cavity diameter,cavity location and cavity head height on the internal force of lining structure.The results show that when there is a pipe type cavity around the tunnel,the inner side of the lining in contact with the cavity bears a large positive bending moment,which is the most unfavorable stress position of the lining structure;With the increase of cavity diameter and water head height,the internal force of lining increased significantly;The location of the cavity affects the distribution of the internal force of the lining.When the cavity is located at the tunnel vault,the lining structure has the smallest water pressure resistance capacity.