Study On Seismic Response Characteristics Of Shallow Unbalanced Pressure Tunnel

The previous earthquake damages show that the seismic damage of the tunnel section of the bias tunnel with poor geological conditions and uneven force is more serious,the seismic fortification problem of the tunnel entrance section becomes the key to the construction.Based on the characteristics of shallow bias tunnel,the seismic response characteristics of the entrance section of shallow bias tunnel are studied through data investigation,shaking table model test and numerical simulation.The main contents include:(1)Through the analysis and statistics of the seismic damage characteristics of the tunnel portal section,it is concluded that the seismic damage of the tunnel entrance section is mainly the following three types: Collapse,landslide on the slope of the edge of the cave,damage to the tunnel door structure and damage to the lining structure of the portal section;The factors affecting the degree of earthquake damage are analyzed.(2)The shaking table model test of shallow buried tunnel is carried out.Considering the bias effect of the tunnel slope,the peak value of different seismic waves is input under one-way excitation,and the acceleration time history and strain time history of the monitoring point are analyzed.The study found that the peak acceleration of the slope slope increases with the increase of the elevation,and the internal acceleration of the surrounding rock changes with the elevation.At the same elevation point,the acceleration peak of the slope is greater than the internal acceleration peak of the surrounding rock;When the input acceleration is 0.05g~0.3g,the acceleration peak of each monitoring point has obvious amplification effect;The peak acceleration of surrounding rock outside the arch shoulder of tunnel shows that the peak acceleration of the overhead side is larger than that of the hillside.Due to the existence of the 60°slope of the portal section,the acceleration effect of the rock outside the arch of the portal section is significantly larger than that of the tunnel.The bending moment of the lining is affected by the cyclic load inthe positive and negative directions,and the axial force is subjected to the tensile and compressive cyclic load.The bending moment and the axial force are both greater than the arch shoulder at the arch.(3)The finite element software was used to establish the numerical calculation model under the conditions of unbiased and different bias angles(20°、30°、40°).Based on the results of the shaking table model test,the internal force,acceleration and displacement response of the shallow buried tunnel are analyzed.It is concluded that the eccentric pressure will increase the peak acceleration of the surrounding rock of the lining,the peak acceleration of the upslope section of the tunnel entrance is larger than that of the eccentric pressure section,the magnification factor of the acceleration of the monitoring points on the empty side is larger than that on the hillside,and the effect of the eccentric pressure at the arch shoulder is more obvious than that at the arch foot.The larger the bias angle,the more obvious the acceleration amplification effect,the bias will increase the displacement,and the added value of the arched shoulder and the arch of the biasing section is more obvious.Under the action of earthquake,the internal force of the lining is obvious,and the internal force of the right arm of the biasing section is large,which is the key part of seismic fortification.