Shaking table test for near-valley subway station - Part Ⅱ: Seismic response of the station

Abstract

With the expansion of metro lines in cities especially in megacities, the number of tunnels and subway stations built near urban valley are rapidly growing. However, the influence mechanism of valley on the nearby subway station, which is due to the strong spatial variability of local valley topography during earthquakes, has not been well-understood. In this paper, a series of 1g shaking table tests is performed to investigate the seismic performance of a typical two-story, three-span subway station nearby the valley topography. The stratum is simulated by synthetic model soil (a mixture of sand and sawdust) and the model structure is made by granular concrete with galvanized steel wires. Note that this is done according to the similitude ratio design to ensure the consistency of the structure-soil flexibility ratio between the prototype and the model. The arc-shaped valley topography with three kinds of depth-to-width ratios, i.e. 1/3, 1/4, and 1/8, are designed and fabricated, and a subway station test without valley site was also considered and taken as a comparative benchmark to better understand the seismic response of the subway station affected by the valley topography under harmonic motions and actual seismic records. Result shows that the acceleration response of the top slab of the near-valley structure is significantly larger than that of the case without valley site, and what's more interesting, the subway station exhibits strong lateral racking under the horizontal transverse motion. The active dynamic earth pressure on the sidewall of the near-valley structure is dramatically increasing due to the valley topographic effect. The bending moments of the sidewall close to the local valley is also significantly amplified compared to the benchmark test without valley site, except for the moments of central columns. Results also indicate that, the acceleration amplitude at the top slab gradually increases with the depth-to-width ratio of the valley, and the lateral racking of the near-valley structure is more pronounced when near the valley with a larger depth-to-width ratio under earthquakes.