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Exercise L - Well Draining
Objective
A deep excavation for the construction of a foundation or other below ground activity,
will frequently penetrate below the normal level for the water table in that area.
If the works are in permeable ground and suitable measures are adopted, the
excavation will fill with water to the local water table level.
One method of de-watering is to sink a ring of wells around the perimeter of the
excavation site and by pumping, lower the water table level locally.
The object of this experiment is to show the core of excavation of water local to a
single well.
Equipment Set Up
Additional equipment necessary for this experiment is as follows (not supplied):
1. 6mm bore PVC clear tube x 2m long.
2. Positive Displacement Pump.
3. Motor for Pump.
4. Fine Mesh Terylene Cloth.
The clear PVC tube with the end covered in fine mesh Terylene cloth to prevent the
ingress of soil, is suspended in the centre of the tank, with its covered end about
100mm from the bottom of the tank.
Space around the overflows is kept free by using vertical sheets of perforated metal
as in
Exercise C - Draining Effect of a Tile Line
. The overflows are to be set with their
tops approximately 25mm below the top of the tank. Sand is to be put in the tank
around the PVC tube and between the perforated metal sheets until the level surface
is approximately 75mm below the top of the tank.
Water is poured slowly into the space around the upstream overflow until the water
reaches a level approximately 75mm below the surface of the sand.
