SIMPLEX FOUNDATIONS engineers working in Southend, Essex recently had a rare opportunity to interact with the public when they found only a wire mesh fence screening them from observers instead of the usual high boarding.
This left them open to questions about the job from passers-by watching the Simplex Andes/ Watson 5000 piling rig bore into the cliff overlooking the sea, a mere 10m from their fine grade II listed Georgian terraced homes.
Southend Borough Council engineers drew up the stabilisation plan, for which special funding was sought from the Office of the Deputy Prime Minister.
The scheme was in response to events two years ago when a nearby failure caused the collapse of an entertainment complex, restaurant and bandstand. This prompted the council to consider the potential for other slippage in the area.
The local cliffs have long been known to be vulnerable to failure and a line of piles was installed here in the 1970s.
However, council engineers prioritised building a new stabilising, retaining and reinforcing structure to guard against any loss to the cliff face, the roadway and the historic terrace.
Piles penetrate the deepest potential slip plane, and go 3m into sound clay below. This provides shearing resistance across these zones and inhibits the development of slips above the line of piles. They will be capped with single reinforced ground beams, linked together for the entire length of the terrace.
Working for main contractor Clancy Docwra, Simplex installed 94, 450mm diameter piles at 1.5m intervals to 25m depth. They feature full-length reinforcement cages and were built using 7m temporary steel casing to seal into the underlying clay, after which the bore was progressed in dry unlined conditions.
The piles toe into the ground below the promenade level at the bottom of the cliff to a depth of 2m to 3m.
Listed lampposts on one side of the workspace and protected trees on the edge of the cliff itself posed movement restrictions.
Simplex completed work on the £137,000 job at the end of February and has also won the contract for further stabilisation along the coast at San Remo.