Safety Performance And Seismic Analysis Of Subway Station Reconstruction And Expansion

With the increase of national infrastructure investment,the revision of urban rail transit network is constantly changing,especially the increasing demand for transfer function between the new line station project and the existing operation station,resulting in a large number of transformation of the existing underground station structure.At present,domestic and foreign scholars have carried out a lot of research on the above-ground structural transformation and reinforcement projects,providing them with advanced theoretical and technical support.However,the underground structure is completely surrounded by the interior of the soil.Compared with the above-ground structure,the structure of the transformation site has special characteristics in the force.In view of this,relying on the transfer line 2 of Xi'an Metro Line 8 which has not been built,Study on safety performance of new line station construction close to existing station.emphasis is laid on the analysis of the structural internal force and displacement variation law of existing stations,ground settlement and mechanical behavior of foundation pit support structure during the construction of new stations.In addition,the construction mechanics characteristics and seismic performance of beam-column members and slabs around the station under different side wall renovation schemes are discussed.On this basis,based on different seismic mitigation measures,the seismic performance of the station is optimized,and the seismic absorption effect is compared.The main conclusions are as follows:(1)The maximum vertical displacement of existing station slab structure is positive during the construction of open-cut station.With the advance of construction,the maximum vertical displacement increases first and then decreases,with a peak value of 3.88 mm.The maximum uplift displacement distribution is transferred from side wall area A to side wall area B of transfer node.With the progress of construction,the range of uplift gradually expands.The maximum horizontal displacement distribution of plate structures undergoes a dynamic change from region C to B and then to C.With the increase of the distance between the beam and the construction site,the horizontal displacement decreases and the influence of the construction decreases.(2)The vertical uplift distribution of the long side wall of the underground diaphragm wall is small on both sides and large in the middle.With the depth of the excavation face,the maximum vertical uplift distribution moves down.The horizontal displacement of underground diaphragm wall presents standard internal convex support deformation,and the maximum value lies in the depth range of-10m~-15 m.With the advance of construction,the final accumulative deformation of long and short side walls is 8.33 mm and 7.29 mm,which are less than the deformation control standard value.The steel support produces an arched bending displacement form that approximates the compression bar,and the maximum vertical displacement and horizontal displacement are + 8.07 mm and + 8.07 mm,respectively.Maximum axial force produced by steel support during foundation pit construction is-1547.17 kN,and by checking the stability of the compression bar,it is less than the critical force Pcr=2831 kN,which meets the requirements of stability and strength.(3)Side wall openings increase the longitudinal and transverse internal forces of roof spans and Mid-slab spans adjacent to side wall openings.The distribution of extreme axial force in Fxx direction varies greatly with different opening forms,and the distribution of extreme axial force in Fyy direction is the same.There is a certain relationship between the extreme value of axial force at the weak position and various variable factors.From the angle of side wall reconstruction construction,the horizontal,vertical displacement and internal force of the station slab,the horizontal,vertical displacement and internal force of the beam and column are comprehensively analyzed.It is unanimously concluded that the square single-hole or multihole form and the vertical rectangle form are more reasonable opening schemes.In practical engineering,the form of small size and multiple holes should be chosen according to the size of passenger flow,so as to avoid the form of transverse rectangle or the situation of single hole size being too large.(4)Under the action of earthquake,the displacement values and distribution laws of the column and structural plate of the station are basically the same,and the size shows a certain regularity with the variable factors.The change of the opening scheme only affects the maximum axial force of the side wall of the structure(i.e.the axial force near the opening of the left side wall).In the transverse rectangular scheme,the extreme axial force of the side wall is larger than that of the square scheme,and excessively changing the length L of the hole will cause a drastic change in the axial force extreme value of the side wall;The internal force of the beam-column structure is more affected by the opening scheme than the side wall.Before the opening of the side wall,comprehensive analysis and consideration should be taken into account.When necessary,seismic strengthening treatment should be carried out on the parts of the beam-column with larger force.(5)From the calculation results,it can be seen that under the action of horizontal earthquake,the station structure mainly produces shear deformation in the X direction,reaching the peak value of positive and negative displacement at 7.70 s and 8.50 s respectively.After using the damping layer,the displacement of the foam concrete damping layer is reduced by 13.1%,the maximum principal stress is reduced by 13%,the rubber damping layer is reduced by 4.36%,and the maximum principal stress is reduced by 4.40%.It can be seen that with the increase of elastic modulus of damping materials,the effect of shock absorption becomes more obvious.