Study On The Bottom Drum-shape Deformation Characteristics Of Railway Tunnel With Slightly Slant Stratiform Surrounding Rock Under Horizontal Stress

With the rapid development of railway tunnels in China,more tunnels pass through complex geological conditions.The phenomena like bottom drum occurs frequently in the process of construction and operation.Based on the a tunnel in Suicheng Line of Hurong Railway,,this paper studies the bottom drum characteristics of the gently inclined layered surrounding rock under different horizontal stresses through the analysis of geological structure and in-situ stress characteristics of the tunnel bottom drum section.It is very important for the understanding of the mechanism of tunnel bottom drum and control of the bottom drum.It can also provide experience for tunnel design under similar circumstances.The main contents and achievements are as follows:(1)By analyzing the geological structure and the characteristics of in-situ stress,found that the rock at the bottom of the tunnel is a kind of gently inclined stratified structure in a geostress environment dominated by horizontal stress.(2)By studying the vertical displacement of stratified rock mass at the bottom of the tunnel under different horizontal stresses,found that the vertical displacement of rock increases linearly with the increase of horizontal stress.When the horizontal stress is greater than 8 MPa,the vertical displacement changes faster.Then discussed deformation form of stratified rock and the range of uplift.(3)By studying the vertical displacement of tunnel lining structure under different horizontal stresses,obtained the variation law of vertical displacement of lining structure,and discussed relationship of bottom lining structure displacement of the double-line inverted arch tunnel,double-line inverse-arch tunnel and single-line inverted-arch tunnel.(4)Obtained the stress distribution law of lining structure and the failure situation of lining structure under different horizontal through the stress analysis of tunnel lining structure under different horizontal stress.(5)By calculating the safety factor of tunnel lining structure,found that the safety factor decreases with the increase of horizontal structural stress.Obtained critical value of horizontal stress to satisfy the safety factor of the tunnel without inverted arch,and predicted.the critical value of horizontal stress of tunnel with inverted arch.(6)Through the reinforcement calculation of the tunnel lining structure,found that under the same horizontal structural stress,the maximum amount of reinforcement is needed in the single line invert tunnel,the second is the double line inverted arch tunnel,and the least is the double line non-inverted arch tunnel.According to requirement of tunnel lining structure of safety factor through reinforcement,put forward the horizontal stress range.(7)Obtained the vertical displacement variation characteristics of tunnel bottom,arch roof and bottom layered rock of tunnel with double lines inverted arch under different lateral pressure coefficients by studying the characteristics of bottom heave of tunnel under different lateral pressure coefficients,λ < 1 and λ > 1.(8)Verified the accuracy of the model and the validity of the data by comparing the simulation results with the field displacement monitoring data.