Research On The Seismic Response Of Underground Structures Considering The Soil And Structure Contact

The soil-structure interface for underground structure may deform uncontinuously like separating and sliding when suffering from earthquake action. For its special ability of transmitting stress and strain between the adjacent parts, the mechanical characteristics of interface have great effects on load and deformation behavior of the soil and structure. This paper proposed a constitutive model for soil-structure interface by analyzing deformation mechanism of the contact surface. This model is able to depict the strain hardening and softening behavior, and has been integrated in the general finite element package ABAQUS. The seismic analysis underground model Dakai has been built to simulate contact influences on structure via a great many cases, and some regularities are got. The mainly work and achievements are listed as follow:(1) Based on the analysis of deformation properties of soil-structure interface, the shear mobilized plan of the soil on the interface corresponding to octahedral plane under 3D stress states of unit body, the tangential stress-strain relation is established by applying the 3D elastoplastic constitutive model for soils to the octahedral plane. The normal compressive deformation of the soil on the interface is similar to that of sidelimit condition. Therefore, the normal stress-strain relation of the soil on the interface is established on the basis of the loading-deformation relation under the side-limit condition. Comparisons between the proposed constitutive model and test results of the soil on the interface indicate that the model is capable of reasonably describe the tangential and normal deformation rules of the soil on the surface. Moreover, the strain softening behavior can be depicted by the OCR. Furthermore, the proposed model is integrated in the general finite element package ABAQUS via FRIC to simulate the deformation process of the soil on the interface. The simulations show that the proposed model is able to reflect the nonlinear mechanical behavior of the soil-structure interface.(2) Based on the understanding of sliding failure of contact interface, two kinds of friction coefficients are chosen, while the friction coefficients is m=0.2 and m=0.4. The contact influence on the seismic response of underground structures is analysised considering relative modulus of structure-soil, three material constitutive relations under two kinds of friction coefficients in time domain integral nonlinear finite element model. The material constitutive relations are elastic-soil with elastic-structure, elastoplastic-soil with elastic-structure and elastoplastic-soil with elastoplastic-structure separately. The maximum deformation time between the peak acceleration time and the peak displacement time and the peak velocity time is extracted to analysis. The results show that when elastic-soil contacted with elastic-structure, the average difference of middle column displacement angle between m=0.2 and tie contact is about 5%, and the value is about 2% between m=0.4 and tie. when elastoplastic-soil contacted with elastic-structure, the average difference of middle column displacement angle between m=0.2 and tie contact is about 41%, and the value is about 10% between m=0.4 and tie.when elastoplastic-soil contacted with elastoplastic-structure, the average difference of middle column displacement angle between m=0.2 and tie contact is about 52%, and the value is about 40% between m=0.4 and tie.(3) The contact influence on the seismic response of underground structures at various restraint of the surrounding rock is analysised by changing buried depth of the underground structure, The results show that the influence is great in shallow-buried structure, while the influence is small in deep-buried structure, and the middle column displacement angle decreased with the increase of the relative modulus of structure-soil when the buried depth of the underground structure is certain. The peak acceleration time is the control time to the shallow-buried structure, while the peak displacement time is the control time to the deep-buried structure,and the peak acceleration time is the control time to the shallow-buried structure, while the peak displacement time is the control time to the deep-buried structure. It is because that the restraint degree of the soil gets larger as the buried depth of the underground structure increases, and the natural vibration characteristic of the structure is changed.(4) The seismic response of underground structure decreases with the increase of the relative modulus of structure-soil when elastic-soil contacted with elastic-structure and elastoplastic-soil contacted with elastic-structure for this paper, and when elastoplastic-soil contacted with elastoplastic-structure, the seismic response of underground structure increases when the relative modulus of structure-soil increases first, and then basically unchanged, and then decreases.