Using partial penetrating wells and curtains to lower the water level of confined aquifer of gravel

• We perform pump tests to verify anisotropy of confined aquifer of gravel.
• We perform numerical simulation to inverse hydraulic parameters.
• Co-work of anisotropic aquifer, partial penetrating wells and curtains is utilized.
• We perform numerical simulation to determine the location and length of well screen.
• 4 m long short well screens embedded by partial penetrating curtain is suggested.

To address the difficulties of penetrating and dewatering of a deep and thick confined aquifer of gravel, a dewatering approach that considers the anisotropic hydraulic conductivity of aquifer, co-work of partial penetrating curtains, and partial penetrating pumping wells was developed. Using the deep foundation pit of the southern ventilation shaft of Metro Line 1 in Hangzhou, China, as an example, a numerical simulation model based on finite difference method was established to invert the parameters and determine the co-work of partial penetrating curtains and wells. The anisotropic characteristic of the aquifer indicated that the three-dimensional flow caused by partial penetrating wells produced bigger drawdown. By co-working with the partial penetrating wells, the partial penetrating curtains changed the horizontal flow to a vertical one, lengthened the flow path, and consumed more energy to produce bigger drawdown. Three simulation schemes with different lengths, depths of well screen, and pumping rates were performed. The results indicated that a short screen for the pumping well embedded by curtains resulted in the biggest drawdown with minimum pumping rate. Based on numerical simulations, four pumping wells with 4 m-long screens embedded by curtains were installed inside the excavation zone. The water level declined to the required drawdown, which indicated that the approach is feasible and can provide solutions to problems on similar projects.