Settlement mechanism of soils induced by local pressure-relief of confined aquifer and parameter analysis

By carrying out the in-situ pumping tests on confined aquifer in Tianjin, it is found that the settlement of soils of overlying confined aquifer gradually increases up to down during local relieving, meanwhile, heave appeares in underlying soils. Further analysis, by using three-dimensional fluid-solid coupling numerical model, indicates that the soil-arch effect will form in soils, which has no drawdown and overlies confined aquifer during its local relieving, in the meantime, the additional tensile stress and tensile deformation appeare there, and moreover, the seepage force is the reason why the soils underlying the confined aquifer heave. Furthermore, the law of ground movement induced by long-term local pressure-relief of confined aquifer under different water supplies and site conditions is studied, and the location of the maximum soil settlement under each condition is obtained. The maximum soil settlement appears at the top of stratum which has drawdown under arbitrary water supply conditions, relieving time and permeability ranges of the overlying aquitard. Because the spatial effect of the overlying soils of confined aquifer induced by local pressure-relief of the confined aquifer cannot be taken into account using the layering summation method (LSM), it will underestimate the settlement of soils below the ground surface during its relieving if LSM is adopted based on the settlement correction factor derived from the pumping tests.