04/06/2026
Double casing in borehole drilling means installing two layers of casing pipe inside the borehole instead of one.
How it works:
- Outer casing: Bigger diameter pipe, set through the overburden, weathered rock, and any unstable zones. Cemented in place to seal off surface contamination.
- Inner casing: Smaller diameter pipe, set through the production zone where water enters. This is the pipe your pump hangs in.
Why drillers use it:
1. Poor geology – Collapsing sands, clays, or fractured rock near surface. Outer casing holds the hole open.
2. Contamination protection – Seals off shallow dirty water so only deep aquifer water enters.
3. Deep holes– Gives structural strength for 80m+ boreholes.
4. Caving formations – Stops the borehole from collapsing during drilling and after.
Downside: Costs more and reduces the final borehole diameter, so you need a smaller pump.
