# What is a Casing?
**A casing is a steel tube that is driven, vibrated or screwed into the ground during the construction of bored piles or ground investigations to stabilise the borehole and prevent the surrounding soil from collapsing.** The casing holds back the soil while work proceeds inside the bore.
## How Does a Casing Work?
– The casing is advanced into the ground to the required depth
– Soil is excavated or bored out from inside the casing
– Reinforcement is placed and the bore is filled with concrete
– Depending on the pile type, the casing is then **extracted** (temporary) or left in place (permanent)
## Types
– **Temporary casing** — withdrawn during or after concreting and reused
– **Permanent casing** — remains in the ground as part of the pile
– **Telescopic casing** — multiple casings of decreasing diameter nested inside each other for deep bores
## Application
Casings are used for bored piles in soft or water-bearing soils, dewatering wells, ground investigations and horizontal directional drilling.
## Related Terms
– Bored pile
– Foundation
– Ground investigation
– Steel tube
– Reinforcement
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