Abstract:In China, various transportation facilities have been built on a large scale. Sea-crossing tunnel projects are constructed in many coastal cities, and many underground structures are built on the soft soil foundation in the south region. These are all underground structures on saturated soil, and China lies in the Pacific Ring of Fire, with many cities located in the high-intensity earthquake zone, so the seismic security of underground structures such as tunnels and subway stations is an important subject. The key is to make an accurate calculation of the dynamic response of the underground structure to the earthquake load. The dynamic response of an underground structure in a saturated soil site is very different from that in other types of soil sites. Therefore, the seismic response of underground structure in the saturated soil should be studied with the right calculation model and analyzing method. At present, one widely used method is numerical simulation and calculation. Depending on the soil calculation model it employs, the analytic method can be classified into three types: the total stress method, simplified effective stress method, and fluid-solid coupling dynamic model method. The fluid-solid coupling model, which takes into account the coupling of fluid-solid dynamic response, is a theoretically complete calculation model. Therefore, the method based on the fluid-solid coupling dynamic model is theoretically sound and more accurate. In general, the dynamic response of an underground structure in a saturated soil site needs further study. In this paper, the seismic response of an underground structure in saturated soil is studied based on the fluid-solid coupling dynamic model and ABAQUS in order to get a complete view of the characteristics and rules of the seismic response. We conduct a simulated calculation of the seismic response of an underground structure in saturated soil, with the site soil simulated by the pore pressure element deduced from the fluid-solid coupling dynamic model of fluid-saturated porous media. The example chooses the seismic record of the N-S components of the Ninghe earthquake (magnitude 6.9 aftershock of the Tangshan earthquake) as the seismic input. From the calculation, we obtain the distribution chart of soil pore pressure, vertical displacement of soil-tunnel system, and von Mises stress on the structure. The calculation results illustrate that by the end of the seismic input, the stress distribution is symmetrical. The stress distribution concentrates in the base area of the two sides, and the water pressure mainly distributes in the base and side areas. The pore pressure and vertical displacement of the site soil are maximal in the base area and decrease gradually in the side area. With increase of depth, the vertical displacement of the site soil decreases gradually. The pore pressure and vertical displacement of the site soil distribute symmetrically. The greatest seismic response occurs when the acceleration of the input earthquake wave reaches the maximum. The calculation results also indicate that the pore pressure element deduced from the fluidvsolid coupling dynamic model of the fluid-saturated porous model can be employed as an effective calculation model for the study of all types of underground structures in saturated soil sites.
