With floods and record-breaking rain soaking Australia’s east coast and winter on the way, it’s likely that at some point you will encounter an excess of water on or below your construction site. Here are some important questions to ask as you plan the dewatering of your site.
Dewatering involves removing large volumes of water from above or below ground to allow for construction work (surface and groundwater control). Some examples of when dewatering might be required include:
To manage an accumulation of water on the surface of your worksite, either in open trenches and excavations or in areas with inadequate slope/drainage to drain water away
To create dry, stable soil conditions for excavation and prevent groundwater and soil leakage
To lower the water table for safely excavating deep foundations or tunnels
When working on sites close to or bordered by large natural bodies of water
Erosion can easily occur when water isn’t removed or discharged appropriately, so before you remove groundwater it’s important to understand your site soil profile and the local water table conditions. To ensure the safety and integrity of your excavation, carefully monitor ground conditions before, during and after dewatering.
Weather can also affect the ground conditions on your site. Excavating and dewatering during heavy rain can reduce the infiltration rate for dewatering, and in some cases prevent the process from working. For successful dewatering, keep an eye on the weather forecast and plan accordingly whenever possible.
A range of different groundwater control and dewatering approaches can be used to safely and efficiently remove surface and groundwater from construction sites, depending on the unique criteria of your project. Possible solutions are by:
Here are four dewatering approaches by pumping commonly used in construction.
1. Pumping: Pumps in varying sizes can be used to quickly and easily remove water from the surface of your construction site. Simply place pumps near the affected areas and pump any surface water out.
2. Sump pumping: Under favourable conditions, sump pumping is a relatively straightforward and cost-effective method for dewatering in both soils and rocks. It usually requires a system of drains to collect the groundwater inflow into an excavation area in sumps and remove it with pumps.
3. Wellpoints: A wellpoint dewatering system provides a versatile method of controlling groundwater in a wide range of soil conditions and excavation geometry and can help to stabilise the soil conditions in shallow excavations by temporarily lowering groundwater levels. To achieve this, a series of wells (spears) are installed around the excavation to collect groundwater. Suction is then created using a vacuum pump at the surface to draw unwanted water up to the surface for treatment or discharge.
4. Deepwells: In a deepwell system, the suction lift limitation is overcome by placing the pump down the well. Deepwells are typically used when excavation depths exceed the limitations of wellpoint systems and installed at wider spacing compared to wellpoints. This technique involves fitting a series of deep wells with submersible pumps. These pumps are connected to the surface with a riser pipe that draws water up.
To prevent environmental pollution, certain water quality standards must be met before water can leave construction sites. In most cases, this means that water removed through dewatering will require treatment before it can be discharged.
Dewatering systems work by removing the water from the ground and moving it to a holding tank where larger solids can settle. From here, pending on the contaminants in the water, a water treatment process will be implemented, including but not limited to chemical dosing, chemical reactions as well as physical filtrations.
Once treated, water can be discharged back to site to be used for dust suppression or ground infiltration purposes, or to a storm water or sewer inlet. Depending on the discharge location, the right permit must always be obtained before the discharge of any water.
Coates Engineering Solutions has an experienced, national team available to support dewatering and water treatment projects Australia-wide. Our geotechnical engineers, technicians, licensed drillers and product specialists can help you to design, supply, install and monitor custom dewatering systems to meet your unique project needs. For ultimate peace of mind, Coates offers turnkey solutions to support all aspects of excavation, dewatering and temporary works.
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