Study On Pushover Test And Numerical Simulation Of Seismic Response Of Underground Structures

Simplified seismic design methods and seismic response characteristics of underground subway structures were studied deeply by means of theoretical analysis,model test and numerical simulation in this paper.Referring to the loading model of the forced boundary displacement method,a new type of static pushover loading device for geotechnical engineering was developed,and horizontal unidirectional pushover test of soil-underground structure system was carried out based on the loading device,meanwhile some suggestions for lateral displacement mode of soil in static calculation were given.Combined with the finite element analyses of underground structure,the proposed method was verified,and the seismic collapse phenomenon of Daikai station was simulated.The main research work and achievements of this paper are as follows:1.Simplified seismic design methods of underground structure cross section were compared and analyzed.Seven common simplified seismic design methods of underground structure cross section were systematically combed.The calculation principle,analytical model,parameters,merit and demerit,application,collection of relevant specifications were introduced in detail.Based on the numerical results of underground structure dynamical response,the calculation errors of seven methods were tested with different buried depth,structural stiffness and soil stiffness.The results showed that the response displacement method had the highest accuracy,and the forced boundary displacement method could underestimate the structural response.2.The horizontal unidirectional pushover test of soil-underground structure was designed and completed by referring to the loading mode of applying lateral displacement to soil in the forced boundary displacement method.Two new types of static pushover loading devices for geotechnical engineering were designed,and the corresponding loading device was made according to the form of "Self-balancing type reaction frame +closed model box + two sliding plates".Two test models of particle concrete rectangular underground structure with and without central column were made respectively,and the pushover test was carried out according to the inverted triangle distribution displacement model.Mechanical mechanism,failure mode and shear strain attenuation characteristics of of underground structure under pushover action were studied,and experimental results explained the reason why the structural response was small in the forced boundary displacement method.3.The numerical simulation of horizontal unidirectional pushover test of soilunderground structure was carried out with finite element method.Firstly the rationality of the numerical model was verified by the experimental results,and then the checked numerical model was used to simulate the condition with coordinated deformation of the left and right sliding plates.It was clear that shear deformation occurred in underground structure during coordinated deformation condition,and the interlayer displacement angle attenuated by 8.2% compared with the lateral slide angle.The improved boundary displacement method could correct the lateral strain attenuation problem in the traditional method,and the calculation errors of three displacement distribution forms were analyzed by using the improved method.According to the error analysis results,it was recommended to adopt the lateral displacement distribution form of absolute peak horizontal displacement of each soil layer in the improved boundary displacement method.4.The three-dimensional finite element models of Daikai subway station and interval tunnel in Japan were established with finite element method,and the dynamical response characteristics and disaster process of subway station and tunnel were analyzed,meanwhile the internal mechanism of subway station collapse was studied deeply.The results showed that the high axial compression ratio of the central column confined the lateral deformation of the subway station,and the lateral deformation of the central column exceeded the limit during the earthquake,which led to the loss of the vertical bearing capacity of the central column,then subway station was destroyed.Hereby,the measure of reinforcing the middle column of subway station with square steel pipe to enhance its seismic capacity were proposed,and the seismic performance of subway station after reinforcement was analyzed numerically.