Seismic Response Analysis And Shock Absorption Technology Research Of Tunnel-working Shaft Structure Under End Reinforcemen

With the severe damage suffered by tunnels in several rare and mega earthquakes in recent years,seismic analysis of tunnel structures has received more and more attention,and the study of the performance of tunnel structures under earthquake action has become an important research topic.The shafts of shield tunnels are more susceptible to seismic damage than ordinary tunnel linings due to the complex structure type and sudden changes in structural stiffness caused by cross-sectional discontinuities,especially in the current mega shield tunnels,which may inevitably be close to or even cross seismic faults,and the shafts will be under the action of near-field impulses,making them a weak link in the seismic performance of the tunnel.In the process of shield initiation and reception,the end reinforcement of the connection section between the shaft and the shield tunnel can avoid the occurrence of accidents such as destabilization of the excavation critical surface and ground subsidence,but the effect of such construction measures on the seismic performance of the tunnel-shaft structure during operation needs further study.In this paper,based on the tunnel-shaft project of a high-intensity largediameter submarine shield tunnel,a three-dimensional refined model of the tunnel-shaft considering end reinforcement is established to predict more accurately the dynamic response of the tunnel-shaft structure under seismic action and to investigate the effect of seismic mitigation measures,and to study the dynamic response of the tunnel-shaft structure under different seismic actions including near-field impulse action,mainly are as follows:(1)The effect of end reinforcement on the seismic performance of the tunnel-shaft structure was investigated by analyzing the dynamic response of the tunnel-shaft structure with and without end reinforcement under different seismic intensities.It is found that the stiffness difference between the shaft and the pipe ring connection is reduced due to the soil reinforcement,which reduces the inter-ring tension between the end ring and the internal force of the ring joint and lining.However,the seismic performance of the tunnel at the end of the end reinforcement is changed due to the change of soil,which needs special attention.(2)To address the problem of excessive inter-ring tension and stress concentration in the area near the two ends of shield tunnel end reinforcement,the energy dissipation node scheme based on SMA is adopted.The feasibility of the damping scheme is verified by the seismic response analysis of the tunnel-shaft structure.The seismic response monitoring scheme of the damping node is proposed to verify its damping mechanism and damping effect,which provides a reference for the subsequent SMA damping design.(3)In view of the fact that the shield tunnel may pass through the seismic fault or fault fracture zone,the shaft may be in the near-fault working state.Considering the near-field pulsetype ground motion as the ground motion input,the response mechanism and performance law of the tunnel-shaft structure under the near-field pulse-type ground motion are investigated,and the damping scheme of the tunnel-shaft structure under the near-field pulse-type ground motion is proposed.