Band Drains
The build up of pore water pressure that occurs upon loading onto soft alluvial soil types (such as in embankment construction across flood plains) can make the cost of transferring loads to deep competent layers by foundation and piling techniques too excessive. To alleviate this problem band drains can be installed to provide vertical pathways for water to escape and to significantly increase the rate of settlement.
How the technique works
Band drains consist of a permeable plastic core wrapped in a filter membrane, which is then threaded through a hollow mandrel for installation purposes. A bespoke rig pushes the attached mandrel into the ground to design depth or refusal. The mandrel is then extracted leaving the drain anchored in place in the ground. The drains are usually installed in a triangular grid pattern, typically at spacings of between 1m and 2.5m.
Benefits
- Band drains of up to 18m in length can be used to treat thick deposits of soft and very soft alluvial clays and to treat large areas where upfilling or reclamation is taking place
- Band drains allow 90% of settlement to occur in a time period of months rather than years, resulting in significantly reduced construction programmes and costs
- Vertical band drains can be combined with other ground improvement techniques such as vibro stone columns and vibro concrete columns to smooth out embankment settlement profiles
- Ideal for use in road, rail, ports and airport construction projects
