Study On Seismic Response Characteristics Of Unsymmetrical Loading Neighborhood Tunnel With Shallow Depth

In the southwestern region of China,the geological conditions are complex and the earthquakes are frequent.Some areas of southwestern China are the high intensity seismic region,so it is necessary to solve the problem of tunnel stability under earthquake.For the special terrain and geological conditions,bridge and tunnel lap way and other factors,distance between the left hole and the right hole can not guarantee to meet the requirements of the specification,so many unsymmetrical loading neighborhood tunnel with shallow depth were constructed.Because the response of this tunnel form is not clear under the earthquake,it is also rarely reported in the literature.Therefore,the shaking table model test was used to simulate the response of the unsymmetrical loading neighborhood tunnel with shallow depth,and its response was investigated under the earthquake.In this thesis,the large-scale shaking table test of unsymmetrical loading neighborhood tunnel with shallow depth was based on the National Natural Science Foundation of China project" Seismic catastrophe behavior and anti-seismic performance evaluation of rock slope containing underground caverns"("No.51204125").The response law of tunnel under the action of Wenchuan wave with different directions and different acceleration peaks were analyzed by Midas GTS/NX software.The main contents and conclusions are shown as follows:(1)The large-scale shaking table model test was carried out,and the acceleration and dynamic strain response of the unsymmetrical loading neighborhood tunnel with shallow depth model in different directions and different acceleration peaks of Wenchuan seismic wave were obtained.The incident direction of seismic wave has great influence on the acceleration of tunnel lining,and the influence of Z direction seismic wave is greater than X direction,and the influence of XZ bidirectional seismic wave is greater than one direction.The acceleration response of the left tunnel is larger than right tunnel.Due to the shallow depth,and near the sloping slope,the wave field splitting phenomenon is produced between the left part of left tunnel and the sloping slope.Different types of waves are superimposed to form complex wave fields,and they greatly influence the acceleration of the tunnel lining.The acceleration response of the dome and the arch of the right tunnel are more intense,we should pay special attention during the design under the earthquake.(2)Lining strain is greatly affected by the peak of seismic acceleration.Under the action of earthquake,the tunnel lining is subjected to tension and compression cyclic loading,tension is dominated.The dynamic strain of the right tunnel is larger than that of the left tunnel.Because the overlying strata are thick,under the action of earthquake,the arch foot is the most dangerous area with tension and compression strain changing drastically.In the reinforcement of the lining,the left tunnel should take asymmetric reinforcement,in the vicinity of the temporary surface of the appropriate increase in the rate of reinforcement.The arch of the tunnel should be equipped with two-way reinforcement to prevent tension and compression damage.(3)The three-dimensional numerical model of unsymmetrical loading neighborhood tunnel with shallow depth was established.The acceleration and internal forces of the tunnels under the same working conditions were obtained,and the reliability of the numerical model was verified by comparing the acceleration of the tunnel lining.The axial force,bending moment and shear force of the tunnel cross section and longitudinal direction,they were calculated by the numerical model under the earthquake.The internal force of the arch foot in the cross section of the tunnel is the largest,and the internal force value in the longitudinal direction of the tunnel is not changed greatly.