Wellpoints are essentially shallow wells, which offer an economic and versatile method of groundwater control. Project Dewatering offer wellpoints that have the advantage of being installed relatively quickly in most ground conditions, and are easy to maintain, with similar equipment being used for both large & small scale projects. Their close spacing and use of vacuum is particularly effective in stratified and fine graded soils.
Wellpoints consist of small-diameter tubes with slots near the bottom that are inserted into the ground from which water is drawn by a vacuum generated by a dewatering pump. Wellpoints are typically installed at close centres in a line along or around the edge of an excavation. As a vacuum is limited to 0 bar, the height to which water can be drawn is limited to about 6 meters.
To work at greater depths, Wellpoints can be installed in stages, with the first reducing the water level by up to five meters, and a second stage, installed at a lower level, lowering it further.
Project Dewatering also offer stainless steel ‘self-jetting’ wellpoints which are reusable, as well as being advantageous in limited headroom situations. Commonly wellpoints are regarded as ‘disposable’ consisting of two essential elements, wellpoints & surface pipework.
Wellpoints are installed using either conventional ‘jetting’ methods, which involve pumping water at high pressure (supplied by a jetting pump &/or compressed air) through a steel placing tube, suspended by a 360 excavator. If self-jetting wellpoints are used, high pressure water is pumped directly down the riser.
Project Dewatering has probably the best drilling capability of any groundwater control company in the UK. So in difficult ground conditions such as open gravels or overlying firm clays, wellpoints can be installed by the use a small rotary or hollow-stem auger rig. Drilling also has the advantage of speedier installation times and in groundwater projects where pollutants cannot be dissipated. Normally the bore in each wellpoint is placed is in the order of 100mm to 150mm diameter. The spacing and depths of the bores is dependent on the ground conditions and drawdown requirements, but typically are between 1.0m and 3.0m apart.
Once installed, individual wellpoints are coupled by control swings to a horizontal vacuum header (collection) main. The header main in turn is connected to a 100mm/150mm centrifugal or piston vacuum pump that can typically handle between 25 to 60 wellpoints per pump. Generated groundwater is then pumped along a pipeline to be discharged via a V-notch settlement tank to a suitable point.