Highway culvert cleaning

Project challenge

Highways England had identified the 60-metre-long, three-metre-wide box culvert as needing priority maintenance work under its national flood prevention programme. The culvert, built in 1977, takes a water course called Bramble Brook, leading from a large lake in Markeaton Park on the eastern outskirts of Derby, under the A38 dual carriageway.

Key challenges: the culvert was difficult to access, located away from a road, and areas with hard-standing; it was almost full to the roof with silt and debris; confined space entry was needed to remove the material.

Client comment

“The Lanes team did a very good job. It was hard and dirty work. Much of it had to be done by hand. Their confined space working health and safety measures were spot on, and they worked well with our teams. It was a strong performance
all round.”
Paul Devine, Project Manager | North Midland Construction

Project implementation

Silt samples were scientifically tested to assess potential toxicity. A substantial amount of mobilisation work was carried out:
• Site security (the up-stream end of the culvert is in a popular park).
• Tree trimming.
• A 100-metre temporary road was laid to allow safe access for Lanes vehicles and protect utility assets under unstable ground.
• A scaffold platform was built to gain safe access to the mouth of the culvert.

North Midland Construction built temporary dams both sides of the culvert to control water flow. Excess water was managed with 150mm water pumps.
Culvert de-silting process A safe system of work was devised to allow continuous desilting. A SuperFlex wet-dry jet vac tanker, which has enhanced suction power, was used to break up the compacted silt, and vacuum it up. This was overpumped to a standard jet vac tanker, and taken off-site for disposal. Up to eight personnel worked on the project. Of those, up to four worked in the culvert, wearing wet suits, rescue kits, gas monitors, and harnesses. A two-person rescue team monitored the work and weather conditions from outside the culvert. A site supervisor managed a tag board, recording details of all operatives below ground.
The culvert was emptied at a rate of up to 25 tonnes of debris a day. Other material removed included large tree branches, and construction waste.

Results

• Silt and debris weighing 400 tonnes was removed and disposed of at an authorised waste site;
• All work was completed