Mention “dewatering” to anyone outside of the underground construction trade, and typically, with a blank stare, they’ll ask what is D-watering? Mention dewatering to anyone in the underground construction trade, and they’ll likely state that it is one of the most important phases in the project, as a well designed and installed dewatering system will allow them to complete their project in a safe and timely manner.
Groundwater exists at various depths below grade (ground level), and in simple terms, dewatering is the lowering of the existing water table so that work can be done below this depth. The lowering of the groundwater table can be achieved by different types of dewatering systems and the type of installation is directly dependent upon the soil type and the soil’s permeability (ability to pass water through pore spaces).
Soils can range from:
- Highly permeable, such as coarse sands and gravel that will allow for the pumping of high volumes of groundwater
- Low permeability, such as silts with lower groundwater pumping ability
- Impermeable soils, such as clays
The type of system or systems installed will vary depending on the excavation depth, size and type or types of soil present at the jobsite. When it comes to dewatering, one size does not fit all.