Study On Bearing Mechanism Of Tunnel Anchorage And Surrounding Rock Of Suspension Bridge

With the rapid development of traffic infrastructure in central and Western China,the bridge tunnel ratio of Expressway in mountainous areas is becoming larger and larger,and the number of long-span suspension bridges in deep valleys is increasing.As one of the main bearing structures of suspension bridges,the anchorage bears the huge tension from the main cable and plays an important role in the structural system of suspension bridges.Tunnel anchorage is a type of suspension bridge anchorage.Compared with gravity anchorage,it can fully mobilize the self bearing capacity of rock mass.In order to further clarify the bearing mechanical mechanism of the tunnel anchorage,analyze the influencing factors of the bearing capacity of the tunnel anchorage,and then put forward suggestions on the design optimization of the tunnel anchorage.Based on the science and technology plan project of Guizhou Provincial Department of Communications(No.: 2020-123-015),taking the Kaiyang tunnel anchor project of Kaizhouhu super large bridge as the background,this paper studies the bearing mechanism of tunnel anchor-surrounding rock by means of on-site test,theoretical analysis and numerical simulation.The main work contents and research results are as follows:(1)An automatic monitoring system for the internal force of the tunnel anchor support structure is established.Based on the monitoring data system,the stress state and change law of the anchor plug body and the front anchor chamber support structure during the construction process and the initial operation are analyzed.It is analyzed that the pull-out bearing capacity of the tunnel anchor mainly comes from the self weight of the anchor plug body and the clamping effect of the mountain.(2)Based on Mindlin formula and Mohr-Coulomb strength theory,the limit shear stress state of anchorage boundary on two-dimensional plane under different working conditions is analyzed.The results show that the tunnel anchorage boundary enters the plastic state under 6 times of pullout load,and the range of plastic zone develops rapidly with the increase of load.(3)The influence of parameters on the pull-out capacity of tunnel anchorage under the condition of anchor-rock synergistic bearing is analyzed.The influence laws of the angle between the anchor-rock boundary and the axis of the anchor plug,the width of the front anchor surface and the length of the axis of the anchor plug on the pull-out capacity of the anchor plug are obtained,and then the optimal design parameters of tunnel anchorage are put forward.(4)A three-dimensional numerical simulation model is established to study the displacement,stress and plastic zone development laws of the anchor plug and surrounding rock under different construction stages and multi-stage pull-out loads.The transfer mechanism and bearing capacity of the pull-out load in the rock mass under different working conditions are analyzed,and the mechanical response characteristics and ultimate bearing capacity of the tunnel anchorage are obtained.