Seismic Response Analysis And Damping Layer Effect Study Of Shallow Buried Brick Earth Tunnel

In recent years,with the accelerated pace of infrastructure construction in China,the scale of underground construction has grown rapidly and gradually become an important part of the infrastructure.Among them,the number of tunnel projects and human defense projects has been in the forefront in the world,but a large number of projects face problems such as earthquake damage in use,which has caused incalculable human and economic losses,so the corresponding research on seismic mitigation is imperative.In this paper,based on a shallow buried brick and soil tunnel project in Yantai,the research on the dynamic response law of the tunnel is carried out,and the seismic damping layer is arranged,and the parameters for setting the damping layer suitable for this project are proposed.The specific work is as follows.(1)The finite element method was used to calculate the bearing capacity of this shallow buried brick soil tunnel,and the stability and seismic weakness location of the lining structure as it is now was analyzed.According to the span,burial depth and current status of the lining of this shallow buried brick earth tunnel project,13 typical cross-sections were selected to establish a two-dimensional finite element model.The axial force,shear force and bending moment of each cross-section lining were derived using the load structure method,and compared with the code calculated compressive bearing capacity,shear bearing capacity and seismic bearing capacity of unreinforced masonry members respectively.The results show that all components of the lining meet the bearing capacity requirements,but the vault top,the bottom of the side walls and the masonry intersection are weaker and should be focused in the seismic response analysis.(2)A three-dimensional finite element model is established,and the dynamic response law of shallow buried brick soil tunnel is analyzed by the dynamic time course method,and the effects of different burial depths,different lining elastic moduli and different peak acceleration of seismic waves are derived.The results show that: increasing the burial depth can significantly reduce the peak displacement,while the stress and internal force values are significantly reduced.The maximum displacement values at different burial depths are all at the top of the arch,followed by the bottom of the sidewall and the masonry material intersection.The peak internal force occurs at the bottom of the sidewall,followed by the top of the arch and the intersection;the change of the elastic modulus does not affect the deformation law of the lining.With the increase of elastic modulus,the peak displacement decreases,and the seismic load increases from the stress change;with the increase of peak acceleration of seismic wave,the peak acceleration of lining also increases,and the maximum acceleration value appears at the top of the arch,and the maximum principal stress and peak displacement of the top and bottom of the arch are obviously larger than the rest of the parts.The seismic damping layer of foam concrete material was set,and the seismic damping effect of the damping layer with different elastic modulus and different thickness was studied.The finite element calculation results show that the damping layer can effectively absorb the seismic wave energy and reduce the lining seismic damage.The seismic damping effect of damping layer thickness gradually increases with the decrease of elastic modulus,and the higher thickness can effectively control the lining deformation.After adopting the foam concrete damping layer with lower modulus of elasticity and higher thickness,the maximum principal stress and displacement peak of the lining structure are reduced significantly,and then a reasonable seismic solution is selected: the recommended thickness of the damping layer is 15 cm,the maximum principal stress is reduced by 19.94% and the displacement peak is reduced by15.03%;the recommended modulus of elasticity of the damping layer material is 500 MPa,the maximum principal stress is reduced by The proposed modulus of elasticity of the damping layer material is 500 MPa,and the maximum principal stress is reduced by15.61% and the peak displacement is reduced by 16.42%.In addition,local thickening of the seismic damping layer in the weak area can effectively reduce the seismic response.