An ejector system is somewhat of a hybrid system between wellpoints and deep wells. Ejectors are typically used where the groundwater must be lowered more than 15 feet and the soil is of low hydraulic conductivity so that vacuum application is of benefit to improve soil drainage.
Unlike deep wells which are equipped with individual submersible pumps, an ejector system (also called an eductor system) allows multiple wells to be powered by a single pumping station. Single pipe and two-pipe ejector systems are available. The single-pipe system is typically used when the well casing is less than three inches in diameter, while the two-pipe system requires a minimum 4-inch well screen and casing. The two-pipe ejector is the simplest to install and can be easily removed for maintenance.
However, ejectors are inherently inefficient and their application requires accurate knowledge of site conditions and practical restraints.
Installation & Applications
Since they are not limited in suction lift and have a lower unit cost than deep wells, ejectors are well suited for deep excavations in stratified soils where close spacing is required. Single-pipe ejectors are installed using methods similar to wellpoints while two-pipe ejectors are typically installed by mud rotary drilling techniques.
When a stability analysis of Crane Valley Dam indicated that the structure would be susceptible to liquefaction during a significant seismic event, a rock-fill buttress was installed at the western portion of the dam to increase the factor of safety. Dewatering was required to ensure continued integrity of the dam during excavation for buttress construction. Moretrench installed 136 ejector wells to accomplish the dewatering in the low permeability soils. Read the full project summary here.
Across the country in Manhattan, New York, a dewatering system comprising 106 ejectors was used to facilitate underpinning of, and excavation below, two existing subway tunnels to allow construction of a new cut-and-cover subway tunnel. Read the full project summary here.
For a comprehensive overview of Moretrench’s range of dewatering tools, also see Wellpoints and Deep Wells. For more information on how our services can benefit your next project, contact us today to speak with one of our key experts.