An eductor system (also called an ejector system) is especially suited for deep excavations and stratified soils. As many as 100 eductor wells are commonly activated by a single pumping station although this varies considerably on the volumes of water to be pumped and the lift required. The volumes of water which can be pumped by each system are generally low, typically less than 200 gpm.
Eductor wells are generally used in areas where the soils have a low permeability. Eductor dewatering systems are especially well suited for deep excavations with stratified soils. The eductor wells are installed at relatively close spacing. In this way, the eductor dewatering system design is similar to the array design used for well point dewatering systems. However, eductors/ejectors require only a single stage to effect drawdowns of up to 100+ feet.
Advantages of eductors:
Not limited in vacuum limitation as in wellpoint systems
Can lower water table as much as 100+ feet from the top of excavations
Cost effective when compared to deep wells where close spacing is necessary because of stratification and/or low permeable soils
Effective in soil stabilization by applying a high vacuum to fine grained soils.
In a typical Griffin eductor system, a series of eductor wells are installed and connected to two parallel headers. One header is a high-pressure supply line and the other header is low pressure return line. Both lines run to a central pump station which feeds water under pressure to eductors placed at the bottom of the wells.
The system uses a venturi to draw groundwater into the well screen and up to the surface. In the single pipe packer system the large diameter pipe forms the well casing and a smaller inner pipe forms the return line. Water is pumped under high pressure along the annulus between the two pipes and is forced through the nozzle and venturi. The groundwater is then recovered through the well and into the return pipe, resulting in a stabilizing effect in fine-grained soils.
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