Research On Key Issues In Pseudo-static Test Of Soil Model Box For Seismic Performance Of Underground Structures

With the development of underground space and the large-scale construction of underground structures such as subways and tunnels,the seismic performance of underground structures has became a focused research.Compared with the rich results of the research on the seismic performance of the aboveground structures,the research on the seismic performance underground structures,especially the experimental study,is still far behind.The pseudo-static test of soil model box for seismic performance of underground structure,which can reflect the interaction of soil and structure reasonably,is a kind of experimental techniques suitable for the study of seismic performance of underground structures.However,due to the many unresolved key issues,the pseudo-static test of underground structure is still in the exploratory stage.In this paper,the method of numerical simulation is adopted to establish the finite element model of the soil model box pseudo-static test of the underground structure,and the key issues in the test and their influence on the test results are studied.The main research contents are as follows:1.According to the pseudo-static test plan of the soil model box of the underground structure,a reasonable finite element model was established,and the influence of the important parameters of the soil size in the test was studied.The results show that the surrounding soils of the structure have an impact on the seismic performance of the structure for all underground structures with different buried depths and different structural forms.Therefore,the surrounding soils of the underground structure should not be ignored in the pseudo-static test.2.For typical shallow and deep underground single-span and double-span structures,multiple sets of numerical models are established for pseudo-static tests under different size of soil beside the structure and different size of soil under the structure.By comparing the results of the numeri cal simulation with the results of the Pushover analysis method of the underground structure,the influence of the soil size on the seismic performance of the structure and the stress and deformation of the soil is analyzed.The suitable range of dimensionless soil size in the soil box of the underground structure is given.3.For deep underground structures,limited by the size of the soil model box,it is difficult to completely simulate the real soil size above the structure in the pseudo-static test.This paper proposes a method of covering the surface of the soil on the structure with steel plates and applying equivalent loads to replace part of the overlying soil.The feasibility of the method is verified by numerical simulation.Besides,it is found that the size of the soil above the structure will also affect the model test results,and the appropriate range of the dimensionless soil size above the structure is giv en.4.In order to verify the applicability of the pro posed suitable soil size in the soil model box test for the seismic performance of the underground structure under reciprocating loading conditions,numerical simulations were carried out on the pseudo-static test of the soil model box under reciprocating loading conditions.Taking a shallow-buried single-span structure as an example,the effectiveness of the proposed scheme is proved through comparative analysis of numerical simulation.