Contents
Background
Design/ Check: DCC Engineering Design Group
Contract: NEC 3 Option B
Project Management/ Supervision: DCC Engineering Design Group
Works Duration: 5 months
Year completed: 2020
Works value: £320,000
The Muddiford Leat project was a highway stabilisation scheme situated alongside the B3230 near Barnstaple. The leat itself forms part of an historic mill and is still working to this day. Heavy rain during the winter months of 2019, combined with an already steep angle of bank (almost 70°) supporting the highway, resulted in several local land slips along the leat which required repair to safeguard the stability of the highway.
What were the options?
The B3230 had been closed in this location several times previously, so there was a strong emphasis on keeping the road open for the duration of the works. There was very limited working space on site, so working from the road was the only viable option.
A dwarf retaining wall at the toe of the bank, constructed of mass concrete, was initially considered. However, this had many disadvantages compared to soil nailing. The wall would require more in water works, excavation into the slip would be necessary to maintain the leat width and the proposal would have been a poor solution in terms of overall ‘carbon-footprint’ when compared to other stabilisation techniques.
Soil nailing of the bank was the selected alternative, allowing the works to be completed under two-way traffic lights, minimising the impact on the highway network. In addition, the embodied carbon associated with the soil nail solution was significantly lower than other potential solutions considered.
Who was involved?
Overall, the scheme was managed by a Senior Engineer, with input from another Engineer in the same team. Drawings were produced by a Higher-Level Apprentice. Site supervision was shared between the Engineer and Apprentice.
EDG consulted the DCC flood risk team for consent to work in the leat and continual consultation was had with the mill owners to ensure the impact of the works was minimised.