Water level response in wells to dynamic shaking in confined unconsolidated sediments: A laboratory study

Abstract

This paper focuses on laboratory experiments designed to investigate the influence of dynamic shaking on water level fluctuations in boreholes completed in unconsolidated sediments. A large flume filled with natural sandy sediments was subjected to horizontal dynamic loading at different frequencies (0.5–15 Hz) and accelerations (0.1 g, 0.15 g, 0.25 g and 0.5 g), generated by a shaking table. Thus, the change in characteristics of the water and saturated sediments were investigated, i.e. how water levels and hydraulic properties change with time, are of significant interest. A range of different of water level changes following oscillating pore pressure for hydrostatic and hydrodynamic (flowing) conditions were observed: oscillation, step-rise, step-rise with oscillation, and step-drop with oscillation, similar to those observed in the field after earthquakes. We found that water level declines occur when the imposed frequency is less than 2 Hz, while the magnitude of acceleration shows weak correlation with the water level change when it is less than 0.5 g. Sinusoidal wave propagation reduces hydraulic conductivity first sharply, stabilizes, and is then followed by a constant value with a slight increase. Heterogeneous consolidation, mechanical resonance, compaction, dilation, and re-packing of the grain structure may constitute physically plausible mechanisms for water level fluctuations and hydraulic parameter adjustment. Laboratory experiments can therefore provide an insight and a quantitative process-oriented approach to better understand groundwater level response to seismic waves.