The project asked for the stabilisation of a 900m long slope below which a new sea wall was being constructed.
The location of the project presented the major problem; a SSSI site on the World Heritage Jurassic Coast! Drilling conditions were going to be challenging, owing to the presence of interbedded bands of soft clay and hard shale. This, coupled with access difficulties throughout the site (sea at the toe of the slope & residential property at the crest) created a very challenging working environment.
Initial works included extensive devegetation of the slope; this was completed in stages to ensure protection of dormice and other protected species (including the building of an escape corridor).
CAN Geotechnical provided early contractor involvement, working with Principal Contractor and Designer to improve buildability and reduce costs. This included installation and testing of trial nails, various facing systems and custom-made head plates, resulting in significant savings.
2500 soil nails up to 21m long were installed, which given the difficult site conditions were installed using several different types of drill rig, including long reach excavators, crawler rigs & A-frames.
CAN installed 40 inclined drains, 20-25m long, positioned at the interface of a thin bed of clay with rock bands which required careful and accurate drilling.
Finally, 11,000m2 of Ultracoated Tecco netting was placed on the slope, pre-tensioned with the custom made head plates to provide active restraint in the harsh coastal environment.
Duration: 15 months
Client: Balfour Beatty
Location: Lyme Regis