Principle Contractor: SWH Contracting
Marshalls Civils & Drainage product: Flat-Pack System
The A40 is the original road connecting London to Wales. The busiest sections have been converted to motorway but the section from Higham, Gloucestershire, to Ross-on-Wye in Herefordshire, remains single carriageway. Much of this part of the road runs along a steep hillside and in March 2021 very high rainfall weakened the ground, causing an embankment failure in the Glasshouse Lane area.
This is a challenging section of carriageway on a steep slope approaching the Wye Valley. National Highways monitored the area to design a repair strong enough to take into account potential future rainfall.
From October 2021 to May 2022 counterfort drains were installed to bring down water levels within the bank to a safe level. After this was done, work could start on rebuilding the embankment. Reconstruction of the embankment began in August and was completed in early March 2023. The work involved installing a new safety barrier and strengthening the embankment with soil nails.
The first phase of the project involved installation of the drainage system. SWH Contractors installed 100m of filter stone along the line of the road with four access chambers and the Marshalls Civils & Drainage Flat-Pack manhole situated at the lowest point.
The design incorporated a toe-drain at the bottom of the embankment and run-off drains feeding into the Flat-Pack manhole. Water running off the road surface is intercepted and channelled through the counterfort drains into the Flat-Pack manhole. From there the water runs to the 1500mm Perfect Manhole which has three inlets and one outlet which drains into a headwall and from there into the local water course. The embankment is steep and extend 6m from the top (verge) to the bottom of embankment.
Marshalls designed and supplied a rectangular manhole from its Flat Pack system, manufactured as a bespoke unit to facilitate site requirements specification for the verge manhole (at top of embankment) required a reinforced manhole with sides 300mm thick and a 500mm sump at the base. It has two inlets – one 300mm in, the other 150mm – and one 300mm outlet. The outlet from the verge manhole drains into the 1500mm Perfect Manhole at the bottom of the embankment.
“The products were supplied through our supply chain partner, Keyline, which is a Marshalls distributor,” says SWH Contracts’ site manager Lee Allen. “The verge manhole is a bespoke unit. It basically had to be Marshalls, but I went out to four companies to compare prices and availability. Marshalls came back to me within a week. “I use a lot of Marshalls products, like kerbs and linear drainage products, so I’m familiar with the Marshalls product range and I’m confident about the quality of its products and service,” adds Mr Allen.