Greater drawdown levels and the ability to overcome the limited suction lift of wellpoints can be made by the installation of Deep Well Dewatering systems. Deep Wells are also advantageous where there is limited space to install wellpoints close to an excavation, as Deep Wells can be located at a distance to generate the required drawdown. Deep Wells are also used for water extraction wells, groundwater remediation and as a point of recharge in pumping systems.

Project Dewatering Ltd offer effective and innovative sub-contract solutions to groundwater problems using Deep Wells. We offer a full professional service from initial design, drilling, supply and installation of pumping equipment together with site management throughout.

The design of Deep Well and Ejector Dewatering Systems are more complex than for Wellpoint schemes. Principally, because of the remote locations, Deep Wells rely on the interaction of individual drawdown profiles, to produce the desired total drawdown. Typically, the spacing of Deep Wells is between 5m to 25m. The terminal depth of a Deep Well is dependent on the required individual well yield and the drawdown profile. This in turn is a function of soil permeability and characteristics, target drawdowns and spatial parameters. With the susceptible nature of this, good initial design relies on Pumping Test Data.

Deep Wells typically consist of vertical or inclined bores, usually in the order of 200mm to 300mm diameter placed through the strata requiring dewatering or pressure relief. A suitable uPVC liner will be placed in the borehole, consisting of screened and cased sections. An adequate filter pack is installed to both maximise well yield and inhibit the movement of fines. After well development, typically airlifting in granular soils, or acidisation in hard Chalk, a suitable electric submersible borehole pump is installed.

Project Dewatering Ltd has probably the best drilling capability of any groundwater control company in the UK. We can use a variety of drilling methods to deal with all ground conditions such as, Cable Percussive (Shell & Auger) Auger and Rotary drilling techniques using polymer, water and air flush methods. It cannot be stressed enough, the need of good wells as the best designs can fail, if wells do not perform due to poor construction.

Wellpoints

Wellpoints are essentially shallow wells, which offer an economic and versatile method of groundwater control. Project Dewatering Ltd can offer wellpoints that have an advantage of being installed relatively quickly in most ground conditions, and that are easy to maintain, with the equipment being the same for both large & small scale projects. There close spacing and use of vacuum can lead to effective results in stratified and fine graded soils. The disadvantage is the limited suction lift, between 3.0 to 6.0m, and the on-site aggravation of having a surface pipework around the excavation.

However, greater drawdown levels can be achieved by a multi-stage design. Project Dewatering Ltd can 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 Filter-screen section (250mm, 500mm, 1.0m) protected by either a nylon or ‘Coco’ filter wrap. Riser – nominal 50mm dia uPVC pipe. Stainless steel self-jetting wellpoint filter (1.1/2”) & 1.1/2” steel riser.

Surface pipework Flexible control swing 6” &/or 8” vacuum header (collection) main 4” &/or 6” centrifugal vacuum pump (Diesel or silenced) and 6” silenced piston pump 6”/8” suction/discharge

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 Ltd 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. Which 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.