Dynamic Response Test And Simulation Analysis Of Subway Tunnel Under The Impact Of Building (Structure) Demolition Collapse

In order to alleviate the increasingly serious urban traffic pressure,subway construction in major cities in China has made rapid progress.Under this background,more and more demolition projects of buildings(structures)near subway tunnels are carried out.Due to the significant differences between the impact of high-rise building demolition collapse bodies and other impact loads in terms of generation mechanism,propagation law and dynamic characteristics,the dynamic response mechanism of subway tunnels under collapse impact vibration is not clear yet,and the safety evaluation and protection are not scientific enough.This paper aims at the situation where there are subway tunnels near demolition blasting projects,and proposes a research method combining model test and numerical simulation.According to similarity theory,a scaled physical model is designed and fabricated,and an experimental scheme and a test scheme for dynamic response of subway tunnel under collapse impact load are formulated according to actual conditions.The dynamic strain and soil pressure of subway tunnel under impact load are collected.Meanwhile,ANSYS/LS-DYNA finite element software is used to numerically simulate the model test.Combined with the results of model test,the validity of numerical model materials,parameters and results are verified.The dynamic response of subway tunnel under collapse impact load is analyzed by combining numerical simulation with model test.At the same time,based on a 24-story frame structure building demolition blasting project which is only 6.5m away from subway tunnel,a systematic study on dynamic response characteristics of subway tunnel under collapse impact load is carried out by combining field test with numerical simulation.The current national standard “Blasting Safety Regulations”(GB67222-2014)on vibration influence safety evaluation standard for traffic tunnel is discussed.The main conclusions are as follows:1.The stress distribution of soil under collapse impact load is almost uniform,and the shock wave propagates on the soil surface mainly in the form of surface waves and in the soil in the form of body waves.After the stress wave reaches the subway tunnel,the stress distribution form changes,and stress concentration occurs on the contact surface between the tunnel and soil.2.The tunnel model undergoes elastic deformation under the impact of a 50 kg,30 m high falling load.The dynamic strain on the cross section is mainly circumferential strain and secondary axial strain.And under different working conditions,the tunnel model starts to show stress at different times.The tunnel model strain gradually decreases with the increase of horizontal impact distance.When impacted directly above,the tunnel model strain reaches the maximum,followed by the waist and bottom of the tunnel.And the dynamic response of the tunnel model shows relative lag as it moves further along the axis direction.3.The numerical simulation results of stress change law are consistent with field test results,and numerical difference is within error tolerance range.Combined with numerical simulation and model test results,validity of numerical model materials,parameters and results can be verified.Therefore,it is feasible to study dynamic response of underground tunnel under collapse impact load by numerical simulation method.4.Among column blasting,building seating,cut closure and tipping ground vibration,high-frequency vibration caused by blasting will cause larger vibration velocity for subway tunnel structure but no obvious additional stress;while lowfrequency collapse impact vibration during building cut closure will cause more obvious additional stress for subway tunnel segment.If subway tunnel segment structure has internal damage or construction defects,existing cracks may expand or delamination spalling may occur.Attention should be paid during blasting construction process.5.The vibration of subway tunnel caused by the collapse impact of blasting demolition of a 24 story frame structure building is equivalent to the structural vibration caused by the magnitude III earthquake intensity.There are no domestic evaluation standards for safety and influence of subway tunnels under collapse impact load;current Blasting Safety Regulations(GB6722-2014)followed by blasting design and construction units and Technical Specifications for Safety Protection of Urban Rail Transit Structures(CJJT 202-2013)followed by subway operation management units have not fully considered vibration load source location,vibration load source frequency characteristics as well as dynamic response characteristics of subway tunnel structure;they need to be further improved and refined.