Study On Seismic Response Of Asymmetric Double-Arch Tunnel

With the rapid development of China's transport infrastructure construction,the number of tunnel and underground engineering and the speed of construction in China have become the largest and the fastest around the world.At the same time,there have been many earthquakes in our country in recent years,more and more underground projects are facing the threat of earthquake, so the anti-seismic research of underground engineering become imperative nowadays.Based on an underground excavation tunnel, the seismic dynamic response of asymmetric double-arch tunnel was studied by methods of numerical calculation,and the anti-seismic measures which is suitable for this project was studied and put forward eventually.The main work and research results of this paper are as follows:(1)Based on the analysis of the existing examples of tunnel seismic damage, the seismic damage form, influencing factors and damage mechanism of the tunnel are summarized.(2)Through the numerical simulation, the seismic dynamic response characteristics of asymmetric double-arch tunnel are studied. The results show that: The absolute displacement of the top of the mid-partition was larger, the absolute displacement of the tunnel Invert in the large arch tunnel was smaller; Compared with the same location, the peak value of the displacement of the large arch tunnel was smaller than that of the small arch tunnel;The relative horizontal displacement of the vault and the invert and the relative displacement of the arch in the large arch tunnel are larger than those in the small arch tunnel; The bending moment of the skewback near the mid-partition was the biggest, which means this location is easy to be destroyed in the earthquake; The skewback and spandrel near the surrounding rock in the large arch tunnel and the small arch tunnel are under great pressure, where the concrete prone to compressive failure; the top and bottom of the mid-partition withstand greater shear, where the concrete prone to shear failure; the tensile stress of invert and skewback near the mid-partition in the large arch tunnel and small arch tunnel are larger,where the concrete prone to tension failure; the spandrel and the skewback near the surrounding rock and the mid-partition are subjected to greater compressive stress, and the concrete is easy to crush; the plastic zone of the surrounding rock was all the tensile failure,rather than shear damage; the plastic zone of the surrounding rock was mainly distributed in the vault, the invert, the right spandrel of the large arch tunnel, the left spandrel, the left skewback of the small arch tunnel,and the top and bottom of the mid-partition.(3)The effect of two anti-seismic measures of shock-absorbing layer and grouting reinforcement was studied by numerical calculation. The results show that: setting the shock-absorbing layer increases the peak value of the bending moment of the top and bottom structures of the mid-partition; the peak value of the moments of the vault and the invert of the large arch tunnel was greatly reduced; the peak value of the moments of the small arch tunnels are increased in different degrees; the peak value of the axial force of the lining structure of the large arch tunnel and the small arch tunnel was generally reduced; the peak value of the shear strength of the largest lining structure on the same cross section was greatly reduced, so that the shear force on the same section was more uniform; the peak value of the bending moment of the mid-partition by the side of the large arch tunnel lining has a greater increase after the grouting reinforcement measures, while the other side of the small arch tunnel was slightly reduced; the peak value of the moments of the vault, the arch and the invert of the large arch tunnel are reduced, and the same location was the opposite of the small arch tunnel; the peak values of the axial forces at the two skewbacks of the mid-partition are reduced, while the peak values of the axial force of the skewbacks away from the mid-partition increases; the variation of the peak values of the shear forces was small after the grouting reinforcement measures. The effect of grouting reinforcement on the internal force response and displacement response of the structure is obvious. The larger the grouting range,the greater the maximum displacement and the internal force decrease.However, with the increase of the thickness of the grouting, the influence of the increase of the grouting thickness on the displacement response and the internal force response is weakened, and the decrease of the displacement and the internal force is getting smaller and smaller,which means the grouting reinforcement has the optimal thickness.Prom the simulation results in this paper, the optimum thickness of grouting is 1.8m.