Shaking table test for near-valley underground station: Influence of diaphragm walls

Diaphragm walls are commonly employed as a permanent support for the building of metro stations near urban valley, and in conjunction with the interior sidewalls of the station structure to withstand the pressure from surrounding soils. Despite their prevalent use, the effect of underground diaphragm walls on the seismic response of stations is not yet fully understood. In this paper, a series of 1-g shaking table tests is designed to investigate the seismic response of a near-valley station with underground diaphragm walls within the elastic range. Modeling the stratum-structure-diaphragm walls system is accomplished by employing granular concrete reinforced with galvanized steel wires and synthetic model soils, and a station without diaphragm walls is included, serving as a benchmark for comparative analysis to understand the influence of diaphragm walls on the seismic behavior of the station. The experiment was designed for three depth-to-width ratios (DWRs), i.e. 1/3, 1/4, and 1/8, of arc-shaped valley topography, as well as the seismic excitations for the test include actual seismic records with the amplitude of 0.2 g, 0.4 g, and 0.8 g, respectively. Results show that the underground diaphragm walls enhance the lateral stiffness of the near-valley station compared to structures without diaphragm walls, and thus significantly reducing the racking deformation of structure during earthquakes. The presence of diaphragm wall would decrease the amplification of dynamic earth pressure caused by valley effect at the structural sidewalls, and significantly reduce the lateral vibration and shear effect of the station near a valley with a larger DWR. Notably, bending moment response at the connection between the diaphragm walls and structural sidewalls are dramatically amplified under strong seismic loading, and such adverse effects gradually increase with the DWR of the valley.