Groundwater Control Dewatering for trenches up to 6 metres deep either by : sump pumping or ; sump pumping or ; well pointing well pointing

Sump pumping or Well Pointing The choice and the effectiveness of the method depends on : nature of the soil nature of the soil the proportions of the trench the proportions of the trench the degree of groundwater drawndown the degree of groundwater drawndown

Sump pumping or Well Pointing pumping tests may be required to determine the final choice of the method to be used pumping tests may be required to determine the final choice of the method to be used If neither sump pumping or well pointing is practicable, other control methods must be considered. If neither sump pumping or well pointing is practicable, other control methods must be considered. Approximate zones of application of various dewatering processes are shown in the figure below. Approximate zones of application of various dewatering processes are shown in the figure below.

Sump Pumping..\Teaching_Notes\TEMP_WK\multimedia\Grdwaterctrl-dewatering0.jpg..\Teaching_Notes\TEMP_WK\multimedia\Grdwaterctrl-dewatering0.jpg

Sump Pumping simple and cheap to install simple and cheap to install for highly permeable soils e.g. gravels, moderately permeable sand-gravel mixtures for highly permeable soils e.g. gravels, moderately permeable sand-gravel mixtures used with watertight trench sheeting to limit the groundwater flow used with watertight trench sheeting to limit the groundwater flow

Well-pointing..\Teaching_Notes\TEMP_WK\multimedia\Grdwaterctrl- dewatering1.jpg..\Teaching_Notes\TEMP_WK\multimedia\Grdwaterctrl- dewatering1.jpg..\Teaching_Notes\TEMP_WK\multimedia\Grdwaterctrl- dewatering1.jpg

Well-pointing installed at 0.6 to 2.0 metres centres on one or both sides of the trench installed at 0.6 to 2.0 metres centres on one or both sides of the trench effective in lowering the water by 4 to 6 metres effective in lowering the water by 4 to 6 metres good use for in sands, heavy flows in permeable ground e.g. gravels good use for in sands, heavy flows in permeable ground e.g. gravels

Well-pointing not good for impermeable clay not good for impermeable clay efficiency increased by ‘ sanding in ’ the well point and riser using a column of sharp sand efficiency increased by ‘ sanding in ’ the well point and riser using a column of sharp sand

Uses of Different Well Point Systems single-sided well point for uniformly graded sand single-sided well point for uniformly graded sand double sided well point for soils of medium permeability, sand overlying clay, fine-grained soil double sided well point for soils of medium permeability, sand overlying clay, fine-grained soil double sided multi-stage well-point system for sands, sand-gravel mixtures. The method increases effective depth of drawdown but requires careful planning double sided multi-stage well-point system for sands, sand-gravel mixtures. The method increases effective depth of drawdown but requires careful planning

Uses of Different Well Point Systems..\Teaching_Notes\TEMP_WK\multimedia\Grdwaterctrl-dewatering2.jpg..\Teaching_Notes\TEMP_WK\multimedia\Grdwaterctrl-dewatering2.jpg..\Teaching_Notes\TEMP_WK\multimedia\Grdwaterctrl-dewatering2.jpg..\Teaching_Notes\TEMP_WK\multimedia\Grdwaterctrl-dewatering3.jpg..\Teaching_Notes\TEMP_WK\multimedia\Grdwaterctrl-dewatering3.jpg..\Teaching_Notes\TEMP_WK\multimedia\Grdwaterctrl-dewatering3.jpg