Stability And Reliability Study Of Tunnel Anchorage

In recent years,tunnel anchor has been widely used in major suspension bridges due to its advantages of small earthwork excavation,friendly environment,low cost and strong bearing capacity.With its extensive application in engineering,it is particularly important to study the overall safety of tunnel anchor structure.Based on the National Natural Science Foundation of China,starting from the working mechanism of tunnel anchor,combined with the mechanical parameters of surrounding rock in the anchorage area of a Yangtze River Bridge tunnel,this paper studies the stability of this type of tunnel during the anchorage stage and the influence law of its influencing factors by means of theoretical analysis and numerical simulation,and applies the method of neural network and first-order reliability analysis to this type of tunnel.The reliability of anchor safe operation is studied.The main research results and work are as follows:(1)Based on the analysis of the geological conditions of a tunnel anchorage project of the Yangtze River Bridge,combined with the field monitoring data,and using the method of orthogonal test,theoretical analysis,numerical simulation and neural network,the reasonable inversion of the mechanical parameters of surrounding rock is carried out,and the elastic modulus of surrounding rock E=4297 MPa,cohesion c=524.75 kPa,internal friction angle phi=35.2 degrees are obtained.(2)Considering the topographic characteristics of mountain body,the load-bearing stability of actual tunnel anchor engineering is studied by three-dimensional numerical simulation.The results show that under the design load,the deformation values of anchor plug,surrounding rock and slope support all meet the requirements of the code;the stress of surrounding rock is mainly shear stress,and there is no plastic zone.Under the action of overload,the tunnel anchor mainly drives the deformation of the area above 15 meters at the bottom of the anchor plug body;with the increase of load,the peak shear stress of surrounding rock gradually shifts from the anchor surface behind the anchor plug body to the rock mass near the anchor-rock interface about 5 meters away from the anchor surface.(3)Based on the working mechanism of tunnel anchor,the influencing factors(including the depth of tunnel anchor,the length of front anchor chamber,the spacing of anchor plug,the expansion angle of anchor plug,the inclination angle of anchor plug,the length of anchor plug and the quality of surrounding rock of anchor site)and the influencing law are studied by numerical simulation.The deformation,stress and the distribution law of plastic zone of surrounding rock under different design parameters are obtained and knotted.Based on the sensitivity analysis of the design parameters by grey correlation method,it is concluded that the sensitivity degree of the safety factor of tunnel anchor to the design parameters is ranked as follows: the length of anchor plug(0.84)>the length of front anchor chamber(0.78)>the buried depth of anchor plug(0.74)>the distance between anchor plugs(0.73)>the expansion angle of anchor plug(0.72).(4)The limit state equation of tunnel anchor reliability research is constructed by using BP neural network,and the failure probability(1.35%)and reliability probability(98.65%)of tunnel anchor are calculated by combining the first-order reliability analysis method,which meets the requirement of target reliability(98%).The influencing factors of tunnel anchor reliability are analyzed,and the variation rules of tunnel anchor reliability under different influencing factors are obtained.