The casing method is applicable for soil conditions are caving
or excessive soil or rock deformation can slough occur when a hole is
drilled. After bore hole is drilled, steel pipe casing is quickly set to
prevent sloughing. The casing is removed soon after the concrete is
deposited. In some cases, the casing may be left in place permanently.
Until the casing is inserted, a slurry is used to maintain the
stability of the hole. After the casing is seated, the slurry is bailed out
and the shaft extended to the required depth. Withdrawl of the
casingdone not carefully, its may lead to voids or soil inclusions in the
concrete