Dewatering can be required on a site where groundwater is present and needs to be removed to facilitate safe construction activities or to prevent water infiltration.
It is important to consult with qualified professionals including geotechnical, environmental engineers and hydrogeologists, when planning dewatering to ensure the safety, efficiency, and regulatory compliance of the project.
Situations Requiring Dewatering
Dewatering can be required in a variety of situations, including:
- Basement excavation
- Tunneling and mining
- Infrastructure projects (e.g., bridges and highways)
- Remediation projects (to remove contaminated groundwater)
- Flood control (use of pumps and drainage systems in low-lying areas).
Importance of Dewatering in Construction Projects
If groundwater has the potential to interact with construction works and dewatering does not occur, several problems can arise that can negatively impact the project’s safety, stability, and timeline. Some of the problems that can occur for a construction project if dewatering does not occur are:
- Soil instability
Excess water in the soil can cause it to become unstable and lose its strength, which can lead to soil erosion, settlement, and even collapse. This can make it difficult or impossible to build foundations, roads, and other structures, and can pose a risk to workers and equipment. Dewatering can also lead to rapid drawdown within embankments, which can lead to slope instability.
- Delayed construction
If excess water is not removed from a construction site, it can cause delays in the construction timeline as work may have to be postponed until the area is dry (i.e. safe) enough to work on. This can lead to cost overruns, missed deadlines, and other project management issues.
- Safety hazards
Excess water in a construction site can create safety hazards for workers and equipment, such as slippery surfaces and sinking machinery, and working platforms for large construction plant can become degraded. All of this can increase the risk of accidents and injuries on the job site.
- Increased costs
Dealing with excess water in a construction project can be expensive, as it may require additional equipment and resources to manage the water. Decisions around dewatering can impact costs for soil remediation, repairs, or even fines and legal fees in the case of damage or accidents, or failure to meet regulatory requirements.
- Environmental damage:
Excess water in a construction site can lead to soil erosion and runoff, which can cause environmental damage and contamination of nearby water sources. This can result in fines, legal action, and reputational damage for the construction company.
Dewatering methods
Dewatering methods commonly used at construction sites include sump pumping, wellpoints, deep wells, and eductor wells. The choice of dewatering method depends on the specific site conditions and the nature of the soil and groundwater. Each method has its advantages and limitations, and a professional evaluation is essential to determine the most suitable approach. For each method, the collected water typically needs to be treated prior to disposal.
Sump pumping involves collecting groundwater in sumps or drains and then pumping it out for disposal. It is a simple and cost-effective option suitable for various soil and rock conditions.
Wellpoint system involves the installation of shallow wells known as wellpoints or spears, around the site perimeter. These wellpoints are connected to a common header pipe, which is then connected to vacuum or centrifugal pumps. The pumps create a vacuum, allowing groundwater to be abstracted through the wellpoints. This method is flexible, relatively inexpensive, and effective in sands and sandy gravels.
Deep wells are constructed when deep excavations and a large volume of groundwater needs to be removed. These wells are suitable for soils or rocks with moderate to high permeability and can drain water up to considerable depths.
Eductor systems are used in low permeability soils such as silty sands, silts, or clays. High-pressure water is used to create a vacuum that draws in groundwater through the eductor nozzle and venturi. It helps stabilise side slopes and soil in the excavation area.
Our latest dewatering project – The New Sydney Fish Market
A unique dewatering project that Douglas was involved with recently has been the new Sydney Fish Market where dewatering was required within a cofferdam so that the new basement could be constructed beneath the water in Sydney Harbour. Douglas has been monitoring the dewatered cofferdam for 18-months.
Learn more about the project: https://newsydneyfishmarket.insw.com/insw/new-sydney-fish-market
Douglas Partners’ Expertise in Dewatering
Douglas Partners is committed to taking a comprehensive approach to dewatering by carefully considering site conditions, project requirements, and environmental regulations. Our team of experienced professionals brings their expertise to each project, ensuring that dewatering solutions are tailored to meet the specific needs of each client.
Contact your local Douglas Partners branch here.
