Study On Stability And Mechanical Characteristics Of Tunnel In Layered Soft Rock

The tunnels built in layered soft rock are often faced with the problems of large deformation of surrounding rock and eccentric load on supporting structure,which may lead to collapse of tunnel,large displacement and distortion of steel arch frame,cracking of lining,and will seriously affect the safety of tunnels.According to the design plan of Zhengzhou-Wanzhou high-speed railway,there are 23 layered soft rock tunnels located in Hubei Province.Taking one of the tunnels ??Baokang Tunnel as research object,the mechanical characteristics of layered soft rock tunnel were studied by means of field investigation,field monitoring,laboratory test,and numerical simulation in this paper.Following results have been achieved:(1)The disease information of 13 tunnels in layered soft rock in China were collected,and the correlation of the diseases with the geological conditions of surrounding rock were analyzed.(2)To study the mechanical properties,strength index and failure mode of layered rock,the uniaxial and triaxial compression tests of shale samples from Baokang tunnel with layer angles of 0°,30°,60°and 90°were carried out.The results show that the largest of the elastic modulus is at 0°,the second is at 30 °and 60 °,the lowest is at 90 °;the largest of the compressive strength is at 0°,the second is at 60°,and the lowest is at 30°or 90°.The elastic modulus of the shale increases with its compressive strength and the confining pressure applied.The failure modes are divided into tensile split failure along the layer plane at 0°,shear slip failure along the plane at 30°,and shear failure crossing the layer plane at 60°and 90°.(3)Two sections with typical layered surrounding rock characteristics were selected in Baokang tunnel to measure the surrounding rock pressure,the internal force of steel arch frame and the stress of steel bar in the lining.The measurement results show that the largest pressure and displacement occur at the arch of tunnel.The displacement and pressure on the right side of the tunnel are generally larger than those on the left side,so the pressure on the tunnel is asymmetric.In addition,the stress in the arch part of the steel supporting structure is greater than that in the side wall and the foot.The maximum stress in the steel supporting structure is 320 MPa,which is greater than the design strength of the steel.(4)Using ABAQUS finite element software,the two-dimensional calculation of layered soft rock tunnel is carried out,and the influence of the inclination angle of the layer on the stress and deformation of surrounding rock and primary support is studied.The results show that the displacement on the top of tunnel is larger than that of side wall and foot.when the inclination angle ? is between 45° and 60°,the bias effect is the most significant,and the displacement and force of the reverse tilting side are generally greater than that of the forward tilting side;? is between 75° and 90°,that is,when the rock layer is steep,the tunnel is in the most disadvantageous state.