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Picking the plant

Funchal airport's £250M runway extension is by far the largest infrastructure project ever undertaken on Maderia. With no heavy construction equipment available locally, rigs, cranes and drilling equipment was transported to site from the Netherlands by barge. This meant contractor NGT could not easily bring in alternative equipment if it was found to be inappropriate. Given the difficult and complex ground conditions it was important that the piling method was simple, flexible and robust.

All piles were constructed using 1.5m diameter casing. This was initially rotated or oscillated into the near surface fill using a Bauer BG drilling rig, or a rotator (Leffer RDM 1500 or RDM 2000) or and oscillator (Leffer VRM 1500 or VRM 2000).

Pile bores were advanced through the fill and beach deposits using the drilling rig until further progress became difficult. Below this the bore was advanced by chisel and hammer-grab suspended from a crawler crane.

In some cases boring switched to an Hitachi KH 180 drilling rig with Wirth B6 reverse circulation drilling drive, once a depth of 12m had been achieved. Rates of advance using this equipment were variable. The system was effective, although quite slow in, compact basalt, while large boulders proved particularly troublesome.

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