Characteristics of ground settlement due to combined actions of groundwater drawdown and enclosure wall movement

When a foundation pit is hydraulically connected with surroundings, the dewatering inside the excavation would both induce water-level decline and enclosure wall deflection, which together cause ground settlement outside the excavation. However, the current studies have not fully revealed the settlement behaviour under the combined actions of the above two factors; meanwhile, the individual effect of the two factors on the ground settlement is still indistinguishable. In this study, in situ pumping test and numerical simulations were both conducted to ascertain the above issues. Specifically, a fluid–solid coupling numerical model was developed to simulate a practical foundation pit dewatering test; measured ground settlement and groundwater drawdown were adopted to validate the numerical model; then, a series of numerical simulations were performed to revel the characteristics of ground settlement due to the combined actions of groundwater drawdown and wall movement; on this basis, the individual impacts of the two factors on the ground settlement were separated. Results show that the settlement ratio caused only by enclosure wall movement (ηb) varies in the range of 2.5–43%, depending on the pumping location, pumping time and hydraulic connectivity in strata; ηb is overall greater during the pumping of phreatic aquifer compared to the pumping of confined aquifer, while with the pumping time elapsed, ηb would both decrease apparently regardless of the pumping location.