WORKERS INSTALLING an electricity feed under Gatwick Airport's main runway had to be able to evacuate drilling equipment in six minutes in an emergency.
Drilling for the 180mm diameter, 520m long pipe, to supply the North Terminal, had to be carried out 25m inside a 'restricted area'.
Contractor the Directional Drilling Company chose to use a large Vermeer Navigator D150x300 directional drilling rig for the work. It had sufficient power to cope with the difficult ground conditions and could be disconnected from the drill string and mud mixing equipment and moved in under six minutes.
With a conventional drill head, the firm drilled down to 7m through clay. A mud motor with a drill bit was attached to bore through hard mudstone to 10m.
Another challenge was to avoid sewers and drains, which meant the drill had to rise quickly to the surface from 10m down. After 520m of drilling, the drill hit the planned exit point within 50mm.
The drill head position was monitored using the Digitrack Mark V location system. This worked well, despite having to trace the drill through up to 1.6m of reinforced concrete.