Experimental investigation on the blocking of groundwater seepage from a waterproof curtain during pumped dewatering in an excavation

The interaction between a waterproof curtain and withdrawal wells (or simply, the wall-well effect) is a key factor in controlling the environmental effects that occur during the dewatering of foundation pits. A series of laboratory investigations was conducted to study the changes in groundwater level during dewatering. The influence of the buried depth of the waterproof curtain placed in a dewatering confined aquifer (D), and the filter length of the pumping well (L), is investigated. Based on the laboratory test results, numerical simulations are used to analyse the ground settlement. The relationship between the approximate hydraulic gradients on both sides of the wall (Delta i), or the ground settlement outside the excavation (S), using ratio R-D (D divided by the thickness of the confined aquifer) or ratio R-L (L divided by the thickness of the confined aquifer), can be simulated using a Boltzmann curve. The value of Delta i increases while S decreases with an increase in R-D, whereas Delta i decreases while S increases with an increase in R-L. The value of the contraflexure point of the Boltzmann curve is regarded as the effective value of R-D or R-L. Based on a comprehensive consideration, R-D is suggested to be equal to or larger than the effective value, and R-L is suggested to be equal to or lesser than the effective value.