Case study: mining culverts

Leigh Hall Colliery, Staffordshire.

Land at the former Leigh Hall Colliery had been cleared for a large warehouse complex and the ground thoroughly compacted when a 212m, 1200mm diameter culvert was discovered at an average depth of 7m. Major disruption to the already-compacted ground wasn’t an option, so it was decided to use Benefil.

Pumping equipment was moved to the culvert by offroad vehicles, and access was excavated to one manhole, giving the Benefil team a distance to fill of 135m in one direction and 77m in the other. Under confined space operating procedures, the team took their equipment into the culvert and were able to pump the grout to achieve a complete fill in both directions.

The job was fast and straightforward. Services were isolated from the subway, and the client built a solid brick 9-inch-thick wall at one end of the subway. A similar wall was constructed at the other end, with a hatchway to permit access for the hoses, and small vents.

The Benefil team then strapped to the ceiling of the subway a 60mm MDPE pipe which they extended to the wall at the far end of the subway, a total length of 30 metres. A second pipe was similarly placed to half the distance, and a third to about 5 metres into the subway. The team then filled the 300-cubic metre subway in three days. The grout was produced on site with only two material deliveries required, a significant consideration for the busy city-centre location.

A similar timescale – filling at approx 40 cubic metres per hour – is standard for Benefil applications to any site – mineshaft, pipeline, culvert or other application.