For deep excavations and shafts, deep well dewatering consisting of drilled wells pumped using submersible borehole pumps is an effective groundwater control measure.
Deep well systems typically consist of a number of drilled wells located around the perimeter of an excavation, from which groundwater is abstracted using submersible borehole pumps. When pumped, a groundwater cone of depression is created and the interaction between the cone of depression created by each well results in groundwater lowering over a wide area. Because the technique does not operate on a suction principle so greater drawdowns can be achieved than a wellpoint system.
The design of a deep well system, with the required depth and number of wells is dependant on ground conditions corresponding drawdown profile and well yields. A conceptual model is established and with sensitivity analysis a design model is generated to an accuracy that allows further engineering assessments to be made. Stuart Wells offer a free dewatering design service as part of our quotation and proposals package. Please contact us to discuss any dewatering requirements or groundwater issues you have.
Deep wells are drilled using a rotary or cable percussive drilling rig (typically 200mm to 450mm bore) into which a well liner is installed (typically 100mm to 300mm diameter) with a surrounding filter annulus. To target or protect specific aquifers a bentonite or grout seal is installed. For most projects vertical wells are installed, however where access is an issue or to maximise efficiency in fractured aquifer, wells can be installed at an inclined angle.
After airlift development of the wells to increase efficiency and reduce the risk of pumping fines. Individual submersible borehole pumps (ranging from 74mm to 250mm – 0.55 kW to 30 kW) are installed on MDPE or steel riser pipe to a wellhead arrangement at the surface. In turn individual wells are connected to a common collection main, for final discharge via a v-notch tank. Pumps are operated using either generator or mains power.
Deep Wells 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.
Please contact us to discuss any dewatering requirements or groundwater issues you have.