The Research On Some Chemical And Physical Test Methods In The Analysis Of The Seismic Response Of Highway Bridge And Tunnel Lap Structures And The Influence Of Structural Parameters

In the face of complex terrain and geomorphological conditions,the repair,strengthening,or reconstruction of the bridge-cum-tunnel lap structure in a highway after severe earthquake damage is often difficult and costly.Currently,there are relatively few studies on the dynamic response,dynamic damage characteristics,and structural design parameters of highway bridge-cum-tunnel lap structures in soft rock strata,both domestically and internationally.The related seismic design,seismic mitigation technology,and seismic damage assessment work lack the necessary theoretical support and need improvement.Therefore,this paper aims to provide reference suggestions for the design and engineering application of seismic mitigation of highway bridge-cum-tunnel lap structures in soft rock strata by conducting a series of research works,including shaking table model tests and analysis of structural parameters using theoretical analysis,shaking table tests,and numerical simulations.The research work conducted in this paper and the main research findings are as follows:(1)According to the similarity theory and model test method,the shaking table test of bridge-tunnel overlapping structure with geometric ratio of 1:50 in soft rock stratum is designed,and the purpose and content of the test,the determination of similarity constants,the preparation of the test model,the arrangement of sensors and the seismic loading scheme are introduced.(2)The effect of different excitation peaks on the acceleration response and strain response characteristics of the tunnel lining of the bridge-tunnel lap structure under EL Centro seismic waves is investigated based on the shaking table test results.The test results indicate that the acceleration values of the tunnel lining structure at each measurement point have a significant amplification effect compared to the seismic wave input.They increase significantly with the increase of the peak excitation and the elevation of the measurement point.The tunnel lining structure of the bridge-tunnel lap section mainly experiences tensile deformation along the tunnel depth(longitudinal direction),with the shoulder and the top of the arch being the parts with the maximum deformation in the standard and expanded sections of the lining,respectively.The maximum tensile strains in the tunnel lining structure are found in the standard section near the arch waist and in the elevated arch away from the opening.However,in the expanded section,the maximum tensile strains are found at the top of the arch,but the strain values at all measured points of the lining in the standard section are significantly larger than those in the expanded section.(3)A three-dimensional numerical analysis model of the bridge-cum-tunnel lap structure in soft rock strata is established using the finite element software Midas GTS/NX.The seismic dynamic response characteristics,catastrophic behavior,and variation law of the bridge-cum-tunnel lap structure under the action of EL Centro waves with different excitation strengths are analyzed.(4)The study results indicate that changing a certain structure or design parameter alone has little or no significant effect on the seismic response or catastrophic behavior of bridge-tunnel lap structures in soft rock strata.The combined effect of different combinations of structural parameters should be thoroughly studied to improve the seismic performance of bridge-tunnel lap structures.(5)The results of the shaking table tests and numerical simulations suggest several recommendations.In the design of the tunnel lining structure of the bridge-cum-tunnel lap section of a highway in earthquake zones with strong dynamic soft rock strata,it is advised to strengthen the longitudinal tensile design of the tunnel lining,enhance the seismic design standards and durability requirements of the tunnel lining structure in the standard section adjacent to the enlarged section,increase the lining thickness,pile diameter,and vibration damping layer thickness,or adjust the design parameters of the bridge-cum-tunnel lap structure and the tunnel lining structure.These measures aim to reduce the seismic dynamic response and adverse mechanical effects and meet the requirements of force deformation and overall stability of the tunnel lining under the adverse effects of strong ground vibration.