Carnell worked in collaboration with BEAR Scotland, the trunk road operating company for Transport Scotland’s North East unit, to undertake filter drain refurbishment on the Lhanbryde Bypass and Inverurie Bypass on the A96 in July 2022. 

Using the StoneMaster process to recycle the filter drain media in-situ, provided several carbon, safety and customer benefits over the traditional dig-out and replace method. 

The combined 3,750m length of filter drain was brought back to specification in 11 night shifts, 5 fewer than planned. By only taking away non-compliant material, 787 HGV journeys were removed from the network, while the reduction of materials and haulage alone led to a reduction in CO2e emissions of over 54 tonnes. 

In producing a fully functioning filter drain which will extend the life of the carriageway, StoneMaster removed a tonne of waste every 4.3 linear metres. That included 450 tonnes of surface vegetation and detritus removed at all verge run-off locations. 

Cost and programme savings were made through using a ‘lift & shift’ traffic management methodology. Safety was improved through reduced roadworker exposure, while the risk to road users was minimised through a 79% reduction in HGVs movements in and out of the work zone. 

The StoneMaster process is resilient in the face of record fuel and aggregate prices and the shortage of HGV drivers. 

Commenting on the StoneMaster process, the representative for BEAR Scotland said “This drainage improvement project will greatly improve road user safety. The sustainable process of recycling the filter stone helps reduce lorry mileage and materials required.”