Instability of the slope had damaged the storm drain outfall pipe. CAN was brought in to undertake stabilisation of the adjacent slope at Castle Eden Dene. Here, a brand new outfall pipe was to be built and connected back into the storm drain.
Initially the crest anchor access system was installed and tested just before Christmas of 2016, along with a number of suitability nails, all using a small 5t excavator mounted drill system.
Returning to site in the New Year, the main works to the slope itself were carried out. Drilling took place using A-Frame drill rigs suspended from the crest access system, with the team accessing the slope using rope access methods.
The design coupled with the nature of the ground meant that a grout flush system of drilling was required. Ordinarily, whilst ‘messy’, this wouldn’t present a problem, however with the slope above a stream and the whole site being a SSSI, this meant that special measures would be required! To protect the stream at the toe of the slope, an impermeable barrier was constructed. This ensured that should any grout run down the slope it could not enter the watercourse.
Allowing for installation of the new outfall pipe meant that around 140 soil nails had to be exactly located and drilled / installed to exact lengths and depths. Approximately 680m2 of erosion matting and rockfall netting was installed over the nails. TECCO Green was used for a quick and easy installation.
Once the slope had been stabilised, MMB returned to site. They began tunnelling through the ground for installation of the new outfall pipe, thankfully not encountering any of the soil nails!
Duration: 8 weeks
Client: JN Bentley (Mott Macdonald Bentley)
Location: Peterlee, County Durham