DRAWDOWN OF GROUND WATER CONTROL SYSTEM IN DEEP EXCAVATION SUR-ROUNDED BY CUTOFF WALLS: NUMERICAL INVESTIGATION-Paper

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The study uses three-dimensional finite-difference modeling in MODFLOW to investigate groundwater drawdown around a partially penetrating well inside a square excavation enclosed by partially penetrating cutoff walls. The modeled setting is a homogeneous, isotropic, unconfined sand aquifer. More than 550 analyses examine the effects of well and wall penetration, aquifer depth, excavation size, soil permeability, pumping rate, and well position.<br /><br />The results show that drawdown generally increases when the well is closer to a cutoff wall, the excavation is smaller, the aquifer is shallower relative to wall penetration, soil permeability is lower, or pumping rate is higher. A shallower well—relative to the wall—also tends to produce greater drawdown; extending the well deeper than the wall has little additional effect in many cases. Well-position effects are more pronounced in smaller excavations. For a centrally located well, drawdown profiles in different directions are nearly equal.<br /><br />The cutoff wall creates an abrupt change in drawdown across its boundary. This change follows the same general trends as overall drawdown: it is greater when the well is closer to the wall, the excavation is smaller, permeability is lower, or pumping is higher.<br /><br />The authors present this parametric investigation as a basis for developing a simplified semi-empirical method to estimate drawdown for this type of dewatering system.

Keywords

groundwater drawdown

MODFLOW

finite-difference modeling

partially penetrating well

cutoff walls

unconfined sand aquifer

dewatering system

aquifer permeability

pumping rate

excavation size