A landslip on a slope supporting a section of the B3247 at Keveral Mill in the Seaton Valley near Looe occurred after a period of intense rainfall. Ground settlement and soil creep on a steep embankment had caused the highway to crack and drop by up to 200mm. The highway had been reduced to a single lane controlled by temporary traffic lights.
The slope profile strengthened was approximately 58m long and varied along its length with a retained height between 5.9m and 7.2m with a front face batter between 33º-51º. The solution was completed between December 2014 and April 2015 ready for the start of the Cornish Tourist season.
The works involved:
- Soil nailing and erosion protection.
- Installation of 125 Dywidag R32 self drilling soil nails using our excavator mounted TEI Hem550 drilling mast.
- Installation and fixing of 400 sq. metres of Maccafferi MacMat R.
- Construction of 85 273mm diameter drilled welded steel piles with a central 168mm thick walled CHS installed and grouted 2.5m into bedrock. Pile depth ranged from 8m to 11m.
- Tie backs/ground anchors.
- 16 Dywidag R51/800 self drilling anchors drilled to 8m with 150mm diameter sacrificial bits using our TEI Hem 550 drilling mast mounted on an 18 tonne rubber duck operating the highway on a night time closure.
- Testing of anchorages to BS8081 and TDR PIT testing of completed piles.
- Reinforced capping beam.
- 45m long reinforced concrete parapet shuttered in-situ and later clad in local stone.