Geotechnical Dewatering Techniques
Different types of geotechnical dewatering techniques and their purpose in construction.
Dewatering is a geotechnical process that involves the removal of groundwater from soil or rock in order to reduce the water content to a desired level. Dewatering is a crucial step in preparing an area for construction work. The main factors that determine which dewatering method to use are the depth to which the drawdown has to be conducted and how much the water table has to be lowered.
There are several geotechnical purposes of dewatering, including:
A. Excavation support: Dewatering is often used to support the excavation of foundations, tunnels, or other underground structures. By removing the groundwater, the soil or rock becomes more stable, allowing for safer and more efficient excavation.
B. Groundwater control: Dewatering can be used to control the level of groundwater in a specific area, either to prevent flooding or to maintain a stable water table.
C. Soil stabilization: Removing excess water from soil can increase its strength and stability, making it more suitable for construction purposes.
D. Slope stabilization: Dewatering can be used to stabilize slopes and prevent landslides.
E. Environmental protection: Dewatering can be used to protect against contamination of surface water or groundwater sources.
There are several methods that can be used to dewater a construction site, including:
1. Wellpoint dewatering: This method involves installing a network of small-diameter wells around the perimeter of the excavation site. Pumps are used to draw water out of the wells, lowering the water table and reducing the hydrostatic pressure on the excavation.
2. Deep well dewatering: Deep well dewatering involves the installation of large-diameter wells that are drilled to a depth below the water table. Pumps are used to draw water out of the wells, lowering the water table in the surrounding area.
3. Surface or Sump Pump dewatering: Surface dewatering involves the use of pumps and pipes to remove surface water from the construction site. This method is typically used in combination with other dewatering techniques.
4. Gravity drainage: Gravity drainage involves the use of channels, trenches, or other structures to allow water to drain naturally from the construction site. This method is typically used in combination with other dewatering techniques.
5. Dewatering bags: Dewatering bags are large bags that are filled with soil or other material and placed around the perimeter of the excavation site. Water is drawn out of the excavation site through the bags, which are then removed and replaced as needed.
What are the necessary considerations when choosing a dewatering method?
Type of Soil - Soil permability, rate of flow of water through soil, and soil classification are important factors that dictate the kind of dewatering technique that needs to be used. Sump pumping for example works well in low-permeability soil whereas deep well dewatering performs best in high permeablity soil. Geotechnical engineers and soil data reports are needed to determine the soil type beneath the surface.
Available Budget - Money is the real driver in some situations. Sump pumping is the most cost effective method however it may not perform well for the type of soil on site. Deep well is generally the most expensive method but if its needed then that cost needs to be factored into a project. It is always best to use the correct dewatering technique for the site to avoid poor dewatering or wasting time and money.
Amount of Water - Whether its surface water or groundwater, the amount of water determines the type of dewatering method to use. Wellpoint dewatering works best in shallow aquifers whereas deep well is the only one that can handle an extremely large volume of water. A proper site analysis to determine the amount of water beneath the surface is needed before choosing a method.
Excavation - The depth of your excavation also affects the dewatering process. Deep wells are great for deep excavations, whereas wellpoint and sump pumping works best in small and shallow excavations.