Seismic Response Characteristic And Calculation Method Of Subway Station In Loess

Loess is one of the most widely distributed soil in China, which is mainly located in the central and western earthquake-prone regions. Since the loess has a unique micro structure, i.e. columnar joints, macropore and weak-cementation structure, and is especially sensitive to the effect of water, the earthquake disaster occurred in the loess region is more serious. However, In recent years, the subway engineering in China’s central and western loess region begins to increase gradually. Since the subway station usually serves as a public place with a high population density and large amount of service facilities, the emergency evacuation fo r the customer in the subway station is more time-consuming. Once such a structure encounters an earthquake, the loss will be significant. However, until now, the techniques which are concerned with the seismic behavior of the subway station in loess area basing on the large shaking table test is still in a blank. Correspondingly, any reliable seismic calculation methods for designing the underground structures in loess area is still in a vacant. In this sense, It has a great value for both the academic and engineering field to study the seismic response characteristics and calculation method of the subway station in loess area. The main contents and conclusions in this thesis can be summarized as follows:(1) Initially, the dynamic triaxial tests were conducted to investigate the dynamic behaviors of both the intact loess and remolded loess. The experimental results demonstrate that the dynamic stress and strain curves of the remolded loess show a hardening mode under different experimental conditions: the dynamic stress increases with the increase of the dynamic strain, however, the Young’s modulus of the loess decreases in an hyperbolic manner with the dynamic strain. After that, the nonlinear dynamic characteristic curves for both the intact and remolded loess were obtained by using the nonlinear fitting analysis. The fitting results show that the dynamic shear modulus of the loess decreases with the increase of the shear strain, whereas the damping ratio shows a contrary trend with the shear strain. Such a result obtained in this paper can be used as a benchmark and reference for other experiments and numerical simulation of underground structure in loess field.(2) It is the first time to conduct the shaking table test for subway station in loess field. In the process of designing the shaking table test, a distortion index and its corresponding calculation method were proposed. Such a method can be used to comprehensively evaluate the severity level of the distortion effects generated in the experiment and to improve the reliability of the results obtained from the shaking table test. In the meantime, the mechanical properties of the micro-concrete were studied through the laboratory test. A reasonable micro-concrete mixture ratio was proposed to meet the si milar design of dynamic test. The data acquisition and sensor arrangement position has been optimized according to the results of the numerical simulation of the subway station. The seismic response and disaster characteristics of the loess site and subway station was analyzed based on the results obtained from the shaking table test. It was shown that the research results obtained in this paper can be used as a reliable data for the experimental and theoretical study of underground subway structures.(3) The corresponding numerical simulation, which considers the loess-structure interaction effect, was conducted and analyzed thoroughly for a subway station by using the FE software ABAQUS. A practical method, which is based on the Code for Design of Concrete Structures(GB50010-2010), was proposed to determine the plastic damage index of CDP model. The relevant formula for damage index was also given in this method as well. Meanwhile, a comparison study was carried out to investigate the effect of the artific ial boundary condition in the dynamic response of a subway station in loess area. Then, a modeling technique of coupling finite element with infinite element was put forward. The effects of several factors, including the calculation range of loess field, the interaction effect between the loess and subway station, the mesh size, element types and the input of the initial stress field of the loess filed, were analyzed. Finally, a numerical simulation for the shaking table test of subway station in the loess ground was carried out. The numerical results were compared with the experimental results, where the obtained results verified the reliability of the finite element model.(4) A finite element model was developed for the prototype structure of subway stati on. The internal force distribution, stress response and structure damage distribution of the prototype subway station were analyzed. Basing on the numerical results, several basic principles of seismic design and an enhanced seismic performance method for the subway station in loess area were proposed. Meanwhile, the paper also analyzes the anti-seismic calculation methods for the underground structures. The calculation parameters in the seismic design of the subway station in loess areas were analyzed. The capability of different simplified seismic calculation methods for the subway station was studied. A simplified method suitable for designing the subway station in loess area was put forward subsequently. It was shown that the research results in this paper can provide a reliable reference for the seismic design of underground subway structures in loess area.