Stability And Dynamic Response Analysis Of Tunnel Anchorage Of A Large Bridge Under Complex Geological Conditions

The tunnel anchorage project of a large suspension bridge has some problems,such as uneven thickness of weak interlayer cataclastic rock in surrounding rock,small net distance between tunnel anchorage and adjacent railway tunnel,and anchorage site located in earthquake fault zone.Therefore,the study on the stability and dynamic response of tunnel anchorage system under the condition of complex weak interlayer and high seismic intensity is of great significance to the safety of engineering and the promotion and application of tunnel anchorage in complex geological conditions.In this paper,a refined model of unbonded steel bundle anchoring system with complex weak intercalation is established to comprehensively evaluate the bearing capacity of tunnel anchorage system under weak intercalation from three aspects: deformation stability of tunnel anchorage,mechanical properties of anchor rock interface and mechanical stability of anchorage system.At the same time,the influence of tunnel anchorage construction on adjacent railway tunnel is proved,and the dynamic response characteristics of tunnel anchorage system under different earthquake intensity are deeply analyzed.The main work and conclusions are as follows:1.The anchoring mechanism,failure mode and bearing capacity calculation theory of tunnel anchorage are summarized,and the deformation stability of tunnel anchorage and surrounding rock,mechanical properties of anchor rock interface and stress stability of anchorage system should be considered comprehensively when evaluating the stability of tunnel anchorage system;The failure criterion of tunnel anchorage system is determined.2.Aiming at the problem that the current simplified push-back method cannot take into account the tensile strength of the steel bundle inside the anchor plug body,a refined model of the anchorage system containing unbonded steel bundle is established.The stability of the tunnel anchor is evaluated by comprehensive evaluation method,and the applicability and safety of the tunnel anchor under the complex weak interlayer condition are demonstrated and calculated.The results show that the bearing capacity of the bolt-rock combination of tunnel anchorage is much greater than that of the anchorage system,and its stability is controlled by the tensile ultimate bearing capacity of the steel bundle in the anchorage system.The comprehensive bearing capacity of the tunnel anchorage system is 2.3 times of the design main cable force.3.The overall displacement of tunnel anchorage on the downstream side is larger than that on the upstream side.The overall curve of the center of anchor surface behind the tunnel anchorage,surrounding rock between anchors and surrounding rock outside the anchor presents a "double hump shape" with high left and low right.The compressive stress and frictional resistance at the interface of the anchor plug are abrupt in the weak interlayer area,and the interface stress in the weak interlayer area is obviously less than that in other areas.4.weak interlayer to control deformation and failure of tunnel anchorage anchor the overall displacement of tunnel,anchor rock relative displacement and the interface stress influence significantly,lower the anchor-bearing capacity of rock association of about 33%,anchor body displacement increases about 43% overall.It is suggested that the contact part between the weak interlayer and the tunnel anchor structure should be reinforced by grouting or anti-slip teeth should be set up.5.Simulate the construction process of tunnel anchorage,analyze the force and deformation of tunnel structure during tunnel anchorage chamber excavation and main cable force exerted by tunnel anchorage,and calculate the safety factor of tunnel second lining.The results show that the tunnel settlement increases and the internal force decreases when the anchor is excavated to the weak interlayer,but it has little influence on the safety factor of the tunnel lining structure.Within 5 times of the designed main cable force,it is safe and stable adjacent to the railway tunnel,while over 10 times of the designed main cable force,the safety factor of the second lining of the tunnel does not meet the requirements of the code.6.Synthetic artificial waves of three seismic intensity levels are used to analyze the dynamic response of tunnel anchorages by time-history analysis.It is found that the higher the earthquake magnitude is,the stronger the response of acceleration,displacement and relative displacement of anchor rock is.The stability of tunnel anchorage is good under the action of earthquake and design earthquake.Under the action of rare earthquakes,the dislocation trend between anchor rocks increases,and negative friction resistance appears at the interface of anchor plug body,with the maximum negative friction resistance reaching1.1MPa.The weak parts of tunnel anchorage are rear anchor surface,front anchor surface and loose cable saddle support.7.Under the action of rare earthquakes,the yield failure of rock mass in anchor site is a process of gradual expansion and accumulation.The plastic zone starts from the overlapping area of weak interlayer and tunnel anchorage,and gradually extends to the non-weak interlayer area.