Casing properties

When a hole is being drilled to allow installation of instruments, tools or a pump, the first and obvious requirement is that the diameter of the hole is sufficient to allow easy installation.
If the conditions are such that the hole will be cased then the casing must be large enough to permit the easy running of the pump or other items (the hole in this case, must be larger to accommodate the casing.)
Where flow is to occur along (or up) the casing, the size must also be adequate for the desired flow volume. Since this size is often less than the diameter required to accommodate the pump, it is often possible to run smaller diameter casing; below the pump setting level.
Fluctuations in the standing water level may require deeper pump settings. Advice should be sought on possible drops in the water level before installing a reduced diameter liner that will prevent the pump being lowered.
The casing diameters, recommended in the table below, will admit readily available pumps. Allowance is made so that head losses in the pump column will not bee excessive
Desired yield minimum casing ID
4 L/sec. 100 mm (4 in)
10 L/sec. 150 mm (6 in)
15 L/sec. 200 mm (8 in)
25 L/sec. 250 mm (10 in)
40 L/sec. 300 mm (12 in)
160 L/sec. 600 mm (24 in)
When the well is being constructed to tap sand aquifers (particularly when the aquifers are thin), increased hole diameter and casing diameter may be necessary to assist in constructing a "well entry zone" of adequate diameter.
Casing Thickness must provide adequate strength to withstand both bursting pressures and collapsing pressures Steel casing in a corrosive environmental should be thicker to provide longer life.
Large diameter casings are employed in wells tapping water from very fine, low transmissivity, sands. These are commonly constructed by bucket auger, with glazed tile or concrete casing sections sunk by gravity. The large diameter casing provides storage for peak water supply, which can then be replenished slow by the aquifer.