Seismic Isolation Effects Of Underground Structure And Influence Of Soft And Hard Stratum Boundary

Although the underground structure has good seismic performance,the seismic Countermeasures of the subway station and the seismic response of the underground structure under special geological conditions are still important research topics of seismic engineering.During the earthquake,the deformation of the underground structure is mainly controlled by the relative displacement of the surrounding strata.On the other hand,the stratum displacement at the boundary of soft and hard stratum is relatively concentrated,which has a negative impact on the stress of underground structure.In this paper,based on the analysis of seismic analysis methods of underground structure,the structural deformation and internal force of underground rectangular frame structure under simple earthquake load are calculated,and the dynamic time history method,response displacement method and response acceleration method are used respectively.The effectiveness of response acceleration method is confirmed through the comparison of the three calculation results.Then,taking Taiyuan subway station as an example,using the method of response acceleration,the paper analyzes and compares the isolation effect of the location and thickness of the isolation layer on the subway station.Finally,the dynamic time history method is used to calculate and analyze the influence of soft and hard stratum boundary on the stress of tunnel lining structure.The main conclusions are as follows.(1)With the results of dynamic time history method as reference,the response acceleration method has better calculation accuracy than the response displacement method in the calculation of structural deformation and internal force,and the practicability of the response acceleration method is clear.(2)By using the method of response acceleration,it is clear that it is one of the effective methods for the seismic measures of subway station to set up the isolation layer which is easy to deform in the surrounding strata.The isolation layer can reduce the axial force and bending moment of subway station structure,and has obvious isolation effect.(3)Through the comparative analysis of the isolation effect of six different locations of the isolation layer,it is concluded that when the isolation layer is set around the subway station and the buried depth exceeds 1 m of the station,the maximum bending moment of the structure is reduced most obviously under this condition,which is 40.7%lower than that without the isolation layer.(4)Through comparative analysis of the isolation effect of five different thickness of the isolation layer,we can see that with the increase of the thickness of the isolation layer,the isolation effect has an increasing trend.When the thickness of the isolation layer is set to 1 m,the maximum bending moment of the structure is reduced most obviously,which is 20.9% lower than that of the structure without the isolation layer.However,when the thickness is more than 0.5m,the effect increase is not obvious.In the specific design,the construction and economic factors should be considered comprehensively,and the reasonable thickness of the isolation layer should be selected.(5)Compared with the dynamic time history method,it is clear that the relative position of soft and hard stratum boundary and lining structure has obvious influence on the deformation and stress of lining structure.When the boundary of soft and hard stratum is in the side wall,the lining stress is the largest,while when the overall displacement of the tunnel is the largest,the lining stress is not necessarily the largest,and the displacement difference at the soft and hard boundary plays a major role.