What is Dewatering?
Dewatering systems are routinely used in the construction industry to provide temporary reductions in ground water levels for structures which extend to below groundwater level. A dewatering system generally comprises an array of wells or sumps which are continuously pumped so as to lower the water table to provide stable and dry conditions to facilitate excavation. Dewatering systems may be used around open cut excavations or in conjunction with shoring or retaining walls used to support the excavation. Where retaining walls are used the dewatering well array may be installed internally to exploit the cut-off effect of the shoring arrangements. Alternatively an external well array may be deployed to reduce the hydrostatic loading on the retaining wall or allow use of lower cost shoring arrangements such as contiguous piles as opposed to secant piles.
WJ’s design team, all highly qualified and experienced geotechnical engineers can advise you on the most cost effective and reliable solutions.
Once the structure is completed, or has sufficient structural integrity to resist hydrostatic loads, then pumping can be stopped and groundwater levels allowed to recovery back to their natural levels. Occasionally it can prove viable to provide long term or permanent groundwater control measures to control uplift pressures.
Groundwater control extends this definition to encompass any pumping or recharge system used to manipulate groundwater levels for a range of purposes. Examples include; recharge systems used to limit external drawdown and mitigate environmental or settlement risks or as a means for disposal; vacuum drainage systems for pore pressure control in fine soils; hydraulic barriers used to control migration of contaminates; groundwater lowering used to under-drain and consolidate weak soils; and groundwater lowering to facilitate pile construction.
The choice of pumping system used for dewatering or groundwater systems depends on the amount of drawdown required and the ground conditions; see diagram. The assessment of the ground conditions at a site is generally based on a geotechnical investigation sometimes supported by specialist pumping tests.
Effective management of dewatering systems requires monitoring of groundwater levels and discharge flow rates. WJ provides the necessary performance monitoring using automated data logger system and appropriate geotechnical instrumentation . These monitoring arrangements offer remote data access and GSM alarm alerts for key project staff.
WJ’s installation staff, trained and qualified through our own in house training structure have vast experience of addressing the difficulties typically faced when installing and maintaining dewatering systems.
In fine soils such as silt and silty sand, dewatering is primarily concerned with reduction in pore pressures rather than reduction in the water content. This is because capillary action allows significant reduction in pore pressures, including negative pore pressures, with minimal change in soil water content.
Investment and innovation over a sustained period has resulted in WJ providing the most robust and reliable dewatering equipment. Combined with rigorous design principles you can be certain that your dewatering targets will be met and maintained.
To learn more about the application of groundwater control systems for your project, please browse through the various pages of our website. Alternatively, contact us today via email or call 020 8950 7256.