A key objective for the CRL is to make sure its construction and operation not only minimises any negative impacts to the surrounding environment, but also provides positive benefits.
To protect the built environment, CRL has put in place a state-of-the-art monitoring system.
A component of this is the Cyclops 3D geodetic system that continuously checks for any movement of buildings adjacent to the works. The system works using hundreds of small monitoring prisms and several "total stations” that use lasers to take measurements with extreme accuracy. If any unusual movement is detected, the system alerts the team to take action to prevent excessive movement or damage to neighbouring or affected buildings.
WATER QUALITY / WAI ORA
Digging tunnels is inevitably a mucky business, particularly when it rains.
To protect the harbour and surrounding streets from water contaminated by the excavation works, the construction team implements measures such as protecting stormwater drains using large sediment-catching “socks” and using settlement control systems that remove contaminants from the water.
Looking much like a skip bin attached to water tanks, these settlement systems contain a series of inclined plates forming a large area onto which suspended solids settle, changing muddy water to clear water. Regular testing ensures that the water is free of sediment and contaminants and has a neutral pH, before it is released into the stormwater system and ultimately the harbour.
Waste reduction starts with efficient design: avoiding the use of materials that will later need to be discarded, and reducing the amount of materials that are needed overall.
Construction will always create some waste, so the aspirational goal of the CRL project is to divert all construction waste from landfill. To try to reach that goal, CRL construction teams have been challenged to use the waste hierarchy to avoid, reduce, reuse, recycle and recover as much waste as practicable. This challenge has resulted in some great innovations.
As part of the work to allow the train tunnels to be extended underneath the CPO, deep trenches needed to be excavated by a 100-tonne hydrofraise rig in order to install the reinforced concrete foundation walls that will underpin the building. In several areas this required the floor level to be built up to match that of its surrounds.
The plan was to use compacted crushed concrete backfill and 62 mini piles to support the concrete platform from which the hydrofraise can work.
The revised design, however, uses polystyrene blocks, pumice sand and only 30 mini piles to support the platform. This method is faster, cheaper (by about $450,000) and because the polystyrene blocks will be undamaged, the supplier has agreed to take them back for reuse once the work is complete.
The approach therefore reduces the amount of new material needed (through a reduction in the number of piles needed) and diesel used (for drilling piles and delivering and compacting the backfill) and the polystyrene will remain in good condition so that it can be re-used, for instance as underfloor insulation, avoiding any waste going to landfill.
As well as one-off initiatives to eliminate waste going to landfill, the CRL contractors also have systems in place to deal with the day-to-day waste that is produced and track where it goes.
This ranges from biodegradable office waste collected by We Compost for composting, to demolished concrete being sent to Green Vision for crushing and re-use and general construction waste being sent to Green Gorilla for sorting and recycling. As of July 2017, 40,801 tonnes of waste have been generated, of which 29,956 has been diverted from landfill.
Although the aspirational goal of all waste being diverted from landfill has not been achieved, the charts below show that significant quantities have been diverted.
REUSE OF CONCRETE RINGS
As part of the Albert Street stormwater main realignment, a caisson shaft (large manhole) was excavated at Wellesley Street to extract the tunnel boring machine after it had completed the two-metre diameter stormwater pipe.
Large reinforced concrete ring segments were used to form the shaft and extra ones ordered for contingencies were not needed. Rather than being sent off as waste, these were then used to divert the Orakei main sewer while the original line was being strengthened.
Besides diverting the left-over ring segments from waste, this approach also avoided the use of formwork, reinforcing steel and concrete that would have otherwise have been needed to construct the diversion.