The first shaft was located at Keith Hay Park and is 4.2m in diameter and 76m deep. This task was accomplished using the largest drill rig (LIEBHERR LRB355.1) in New Zealand with a 30m tall mast, 80m long 4 stage Kelly bar, 45 tons of torque on the rotary table and 30 tons of pull on the main winch. The shaft was drilled using specially designed piloting tools and a 4.2m reamer – this methodology was fully developed by CLL. To ensure the shaft verticality (1:200) we constantly monitored using sonar equipment (SHAPE instrumentation) and Jean Lutz devices During the drilling process, the shaft was supported with a customised brew of bentonite as drilling fluid. For temporary support of the 130t of weight from the rig we constructed a secant bored pile wall that extends for 16m below ground level, a collar beam and a designed piling platform. The shaft completed at Keith Hay Park is the deepest shaft of its kind in the country.
CLL is completing another two more shafts for the Central Interceptor tunnel, the next up is a 5.4m diameter, 28m deep shaft at PS23 pump station, and then we will move on to a 4.2m diameter, 63m deep shaft at Walmsley Park.