Innovative solutions overcome challenging large-scale piling project
A significant engineering feat has been achieved in the drilling of large shafts on New Zealand’s largest wastewater infrastructure project– Watercare’s 14.7km Central Interceptor tunnel.
Blick, an Australasian fluid and drilling tools supplier based in New Zealand, was called upon to design a shaft support fluid system that kept a 76-metre-deep shaft open for nearly twice as long as scheduled due to a delay in the arrival of the shaft liner.
The Central Interceptor is a $1.2 billion super-sized tunnel that will reduce wastewater overflows into central Auckland waterways. It is New Zealand’s largest bored wastewater tunnel at 14.7 kilometres in length, 4.5 metres in diameter and runs at depths from 15-110 metres from Grey Lynn under central Auckland and the Manukau Harbour to Māngere Wastewater Treatment Plant.
Piling specialists CLL Service and Solutions is using New Zealand’s largest piling rig with specially designed piloting tools and sonar technology to constantly monitor progress to drill three shafts at Keith Hay Park of 76 metres deep, followed by a 28m shaft in Hillsborough and a 63m shaft in Mt Roskill.
CLL used a SHAFT AREA PROFILE EVALUATOR (SHAPE®), a cost-effective quality assurance testing device for deep foundations such as drilled shafts, slurry walls, barrettes and more to determine the excavation dimensions and verticality. It provides a fast, economical visual representation of the foundation excavation and verticality before placing concrete in wet conditions.
SHAPE® required a viscosity in the support fluid of less than 38 seconds to read the shaft dimensions correctly, and our team redesigned the fluid system to a viscosity of less than 38 seconds while still meeting the design life of 90 days.
The shaft was handed over to the Ghella Abergeldie joint venture 91 days after commencing the pilot. Due to the delay in the shaft liner, Blick was asked to design a unique bentonite-based shaft support fluid system to protect the integrity of the shaft until the liner arrived.
Clay says the support fluid system was designed to allow the hydrated bentonite to flow into the fractures and seal them. M-I SWACO UNITROL, a filtration control polymer, was added to the M-I SWACO MAX GEL to maximise filtration control.
A thin filter cake generated by the M-I SWACO MAX GEL and M-I SWACO UNITROL prevented fluid from moving into the formation from the shaft and allowing hydrostatic pressure to push against it, supporting the 76m deep shaft for an additional 62 days beyond the design specifications with no deterioration.
“The shaft support fluid prevented swelling and provided effective support to the shaft for 152 days, which is an incredible feat,” Clay said.
Blick’s high-quality sodium bentonite M-I SWACO MAX GEL creates a highly effective filter cake with precisely the qualities needed in a piling setting. It is also very effective at holding cuttings in suspension, which is considered a negative side effect during piling.
Blick also specified an additive that, when added to the shaft, caused suspended cuttings to be dropped out of suspension while not impacting the filter cake.
Site engineer Sivam Thivaharan said Blick’s role was vital in protecting the shaft through the liner installation.
“Thanks to Blick and the excellent support of their technical support team, we had a successful outcome from the start to the end of the shaft drilling at Keith Hay Park. We are currently drilling another deep shaft with Blick providing amazing support again,” Sivam said.
CLL is completing two more shafts for the Central Interceptor tunnel, a 5.4m diameter, 28m deep shaft at the PS23 pump station, Fredrick Street in Hillsborough, followed by a 4.2m diameter and 63m deep shaft at Walmsley Park in Mt Roskill.
Blick has been a supplier to Australasia's tunnelling and construction industry for over 50 years. Blick and M-I SWACO partner for water-based drilling fluids across Australia, New Zealand, and the Pacific. They excel in support and advice.
Contact us today if you’re looking at optimising your performance and reducing costs through engineered fluid solutions. Our Australia team is available at +61 3 9068 5688 (Melbourne) or +61 8 6271 3575 (Perth) and New Zealand at +64 7 849 2366.
