CAN acted as Principal Contractor on this major project to stabilise an old quarry prior to redevelopment and the adjacent unstable cliffs situated above inhabited residential properties.
This design and build contract required the stabilisation of a 300m length of rock face up to 60m in height that had suffered a number of failures in recent years, resulting in partial engulfment of buildings at the toe. The design called for major slope reprofiling, soil nailing, rock bolting and the installation of 4-stage 8-strand 2400kN DCP anchors installed to depths ranging from 25m to 30m within the quarry back wall.
Holes for the anchors were drilled with a 191mm dia. DTH drill system utilised a high-pressure (25 bar) air supply fed from an on-site air receiver. Drill arisings were controlled using a mist flush with Hydrocyclone technology to maintain efficiency whilst controlling dust pollution within a town-centre environment.
The anchors were installed from temporary benches. These were formed during the progressive excavation of the failing rock face, using both standard and long-reach excavators. In several areas it was necessary to use sacrificial steel casing to support the collapsing drill hole within broken ground.
For rapid early strength, minimal shrinkage and maximum long-term strength, the anchor grout used a super-plasticiser additive. Post grouting was undertaken to further enhance anchor capacity, followed by multi-stage stressing and testing.
In order to sufficiently distribute the high anchor loads across the poor ground, substantial reinforced sprayed concrete wailing beams were constructed.
The stabilisation of the quarry face has now allowed further residential buildings to be constructed putting this area of land to good use.
Duration: 14 months
Client: Dandara Jersey Ltd & Park Heights Ltd
Location: St Helier, Jersey, Channel Islands