Types of Dewatering Methods

There are many methods that are used to control groundwater levels during an excavation. Thus, selecting the right dewatering method for the site or the project you are working on is the most critical and important step. 

Each site has its own unique set of ground conditions, and therefore it must be assessed carefully. 

When choosing a dewatering method, it is important to attempt to reduce any impact on groundwater resources. 

There are four main dewatering methods used in most of the projects’ sites that require excavation.

These 4 techniques are:-

1) Well Point Dewatering Systems – A flexible, easy-to-install, and cost-effective dewatering solution is the Well Points Dewatering System. These systems consist of a series of a number of shallow wells drilled around the construction site, and these wells contain pumps. These small-diameter wells are further connected to a header pipe and this header pipe is connected to a central vacuum pump. Then, via the header pipe, the vacuum pump extracts and removes water from all of the wells in the system. Thus, the Well-Point Dewatering System is an extremely efficient and effective water removal system.   

These types of systems are ideally suitable for construction foundations, shallow trenches, and utility excavations. Additional well points are required to be installed at deeper levels if the excavation deepens beyond 15 feet. One can not tell the exact depth of the wells in a Well-point dewatering system, as it depends largely on the type of soil, the groundwater control level, and the distance between wells. 

Thus, the well-point dewatering system is highly practical, effective, efficient, and suitable for most soil types and hydrological conditions. For deeper excavations deep well-point systems are more suitable.  

2) Sump Pumping – The most cost-effective and least complex dewatering method is the Sump Pumping method of dewatering. It is a perfect and most suitable method for removing water in shallow excavations and shallow trenches that contain high levels of sand or gravel. 

A sump is defined as a hole lower than the surrounding area where water is allowed to collect. The pump activates once the water reaches a certain height, and then the water is pumped out of it, away from the site.

To remove surface water and shallow groundwater, this method proves to be the most effective method. This method is not ideal for digging foundations or other excavations where soil stability is a concern, because in this method water collects on the surface and is then directed to the hole, lower than the surrounding area, and there is no active water removal from the surrounding soil. 

Typical uses of these sump pumps are to keep basements and other low-lying areas free of standing water.  

3) Educator Well Systems – Educator Well Systems prove to be the best for excavations in soil with low permeability, such as silty sand, silt, clay, etc. These systems are also known as ejector systems. These are specifically designed and engineered to stabilize and maintain pore pressure and lower groundwater levels in deep excavations. These systems operate on the Venturi principle, where high-pressure water circulates through wells as deep as 50 feet. The speed and flow of the water create a vacuum through wells. This pressure of vacuum pulls groundwater through the riser pipe and out of the surrounding soil.

To stabilize the side slopes and soil in an excavation area, these systems are most commonly used. Using this method of educator well systems, one can lower the water table by more than 100 feet from the top of the excavation area. For easier and more efficient dewatering operations, one can operate more than one pump in a single station. 

4) Deep Well Systems – Deep Well Point Dewatering Systems are used for deeper excavations. Particularly, these systems prove to be useful, when there is a large volume of groundwater to remove. Thus, this method consists of boring much deeper and more widely spaced wells, where each well contains an electric submersible pump that is used to lower the groundwater level below the excavation level.  

Deep Well-Point Systems ensure safe and stable conditions in deeper excavations. Sand and gravel have a moderate to high level of permeability, and thus in such soil and rocks these systems are used. There is enough wide spacing between each well of deep well systems, and thus it allows for easy access during each stage of the excavation process.