Vacuum Deep Wells
Vacuum-extracted deep wells are used for groundwater control in regions with low subsoil permeability.
Vacuum-extracted deep wells are operated effectively in aquifers with permeability [k] coefficients ranging from 1x10-5 m/s to 1x10-7 m/s.
They are created by drilling a borehole with a diameter in the range 300 - 700 mm to a depth up to 50 m. Depending on the diameter, the site geology and the intended depth, the borehole can be sunk by dry drilling or straight-flush rotary drilling.
The borehole is then fitted with a wellscreen/casing assembly. The annular void around the assembly is backfilled with gravel. A Bentonite seal is placed above the gravel to prevent the ingress of surface water or contaminants into the borehole. Groundwater abstraction is realized by a multi-stage submersible pump installed in the completed well. Discharge lines carry the groundwater to a discharge point at the surface,
therefore lowering the water table to the desired depth.
The groundwater removal is also assisted by a partial vacuum drawn by a vacuum pump aggregate at the upper edge of the well. The vacuum achieved can range up to 0.9 bar (13 psi). The vacuum provides faster and more wide-ranging drainage even in soils with low permeability, therefore stabilizing the surrounding soil layers.