For most shallow excavations and pipelines vacuum wellpoints offer an economical and effective method of groundwater control.
Wellpoint dewatering systems typically consist of a series of small diameter uPVC or steel riser pipes, that has a filter intake element at the base, that are installed at close centres (typically 1.0m to 2.0m centres) around an excavation or alongside a pipeline trench.
In turn individual wellpoints are connected via flexible control swings at the surface to a collection pipe or header main (galvanised steel or HDPE). This is connected to a vacuum pump (centrifugal or piston type) that abstracts groundwater to a discharge point. Typically, a single pump will operate ~100 lin.m of header main.
Although ground conditions will dictate the dewatering design wellpoints are effective for most excavations up to 5m-6m deep. In fine soil conditions or deeper excavations, the wellpoint system is installed from, and pump positioned at a reduced ground level. For greater depths, if space permits, multi-stage systems can be installed.
Wellpoints are predominantly used for temporary construction dewatering. However, they can be used for permanent dewatering schemes and as a means of abstraction for irrigation or private water supply systems.
Wellpoints are installed using a variety of methods. For most projects’ wellpoints are installed using conventional jetting method. This involves pumping water at high pressure (supplied by a jetting pump and/or compressed air) through a steel placing tube suspended by a 360° excavator. If an upper Clay is present, then wellpoints maybe pre-augured using a hydraulic auger connected to a 360° excavator.
In restricted conditions wellpoints can be installed manually using self-jetting wellpoints (steel or uPVC). In other cases where rock or cobbles are present, wellpoints will be drilled in using a small rotary drilling rig.
For more information on well pointing, please contact Stuart Wells Limited.
