2014 Volume 2 Issue 1 Pages 7-24
The application of negative water pressure by vacuum in pumping wells results in a drawdown of groundwater table at excavation sites. Due to the vacuum, negative water pressure will propagate around the pumping well. As a result, a large potential gradient is induced and groundwater drawdown is enhanced. In the present paper, a numerical model for three-dimensional unconfined groundwater flow towards a pumping well (Deep Well, hereafter DW) is developed and evaluated. First, the accuracy of the model is confirmed by comparing the pumping rates at steady state given by the DW formula. Second, the numerical model for negative water pressure (hereafter, NWP) is described. The model can be used in practical applications together with the water balance equation to describe groundwater inflow and pumping rate in a pumping well so that time-dependent boundary conditions are considered with the three-dimensional groundwater flow equation. How the saturated-negative pressure zone develops around the pumping well is shown. Detailed relationships between water level, pumping rate, and propagation of the negative pressure zone are described and analyzed. The analyses show that the model results can be used to operate air and water pumps more efficiently for water balance and groundwater drawdown.