Wellpoint Dewatering
Wellpoint Dewatering is the most versatile and common form of dewatering able to cope with the low flows from silty sands to the larger flows from course sands and gravels. Wellpoints are installed (jetted in) using high pressure water at approximately 1m intervals on each side of the trench or working area to be dewatered. The wellpoints are connected via a flexible hose swinger to a common header pipe, which in turn is connected to a vacuum primed dewatering pump.
A typical dewatering set is 50 to 68 wellpoints connected to one 150mm (6”) dewatering pump. More than one pump can be used or additional wellpoints added to increase the water drawdown. When pipelaying the dewatering wellpoints are removed and reinstalled daily ahead of the pipeline installation. We prefer to use steel pipe wellpoint spears rather than plastic PVC as galvanized steel spears are stronger and more robust.
Advantages
- Flexibility: the same equipment can be used around small and large excavations
- Quick to install in many soil conditions
- Close spacing (1.5 to 2m typically) promotes effective drawdowns in stratified soils.
Limitations
- A suction lift of 5 to 6m in sands and gravels can be achieved but this may be limited to 3.5 to 4.5m in fine-grained soils
- Headermain can cause access restrictions on site
