J N Bentley working as part of the MMB (Mott MacDonald Bentley) joint venture, selected Polybed over traditional drainage when constructing a new service reservoir in Hanchurch for Severn Trent Water’s AMP6 programme.
Oliver McMahon, J N Bentley’s appointed site agent for the project explained; “The basic concrete structure of the reservoir has a footprint 147m by 72m and once constructed will require a toe drain around the perimeter. The purpose of this is to prevent a build-up of ground water around the structure.”
Traditionally toe drains consisted of perforated pipe surrounded with a gravel bedding and backfill, and a geotextile envelope. Polybed was chosen due to the quick installation time with significant programme and labour savings compared to traditional practise.
The application at Hanchurch required 450 meters of 6” single wall land drain with a geo-textile wrap. Mr McMahon confirmed, “Installation took just 4 days amounting to a programme saving of 10 days verses traditional build” concluding that, “The install has gone very well and very quickly… cost and time savings are estimated to be around 50% on this project.”
Polybed is manufactured by The Forest Group, based in Newent, Gloucestershire, and requires no aggregate on this type of installation as it comes pre-lagged with the required geosynthetic drainage bead and geotextile wrap. Supplied in standard 3m lengths that weigh between 2kg to 13kg depending on product specification chosen.
The product is easy to lift, position and connect in the excavation, just requiring an as dug backfill in most cases. This equates to less labour, plant, operations and less spoil being removed from site. Put simply:- Polybed is the simple to use, no fuss, economical way to construct small diameter drainage and lateral connections from 3” to 6” diameter.
As Used By