Energy, Water and Materials
Although the completed CRL will help to reduce Auckland’s carbon footprint, enabling more Aucklanders to get out of their cars, its construction and operation will consume significant resources.
The project aims to reduce these impacts as much as possible in order to contribute to regional and national greenhouse gas emission reduction targets.
During the design phase, the team sought to optimise resource use for the lifetime of the CRL.
To measure success, total energy, water and materials use was estimated based on the early design ("base case") and the final "detailed design" was compared against it to quantify improvements introduced during the design phase.
The team was successful in achieving projected reductions for both construction and operation, and these projected savings were reported in last year's annual report which can be read here.
Since then, construction is well underway and the team has been tracking resource use on both construction contracts to see how well they are tracking against projections.
During design, the team was able to reduce the projected construction energy greenhouse has (GHG) emissions by over 29% and projected operational emissions by more than 25%. This equates to a total saving equivalent to the GHG emissions associated with almost 18,000 economy flights between Auckland and London.*
The challenge for the construction teams is to stay within these carbon budgets and improve on them if possible. Energy is used during construction for everything from boring piles and transporting excavated spoil to heating water for workers’ tea and coffee. The main reason to reduce energy use is to reduce its associated GHG emissions, measured in tonnes of carbon dioxide equivalent (tCO2e).
These two graphs show emissions associated with energy use for both contracts is tracking well below both the base case and detailed design projections.
Some of the apparent savings that have been achieved in the last quarter of the reporting period may be due to changes in the staging of the works since the original projections were done, but the results are encouraging.
Both contractors are about to enter more energy-intensive phases, with DSBJV about to start piling and excavating under the CPO building and Connectus beginning the bulk excavation of the reinforced trench in Albert Street. Continuing to carefully manage energy use will be key over the next year.
* Based on the International Civil Aviation Organization flight emissions calculator, assuming one way economy travel via Singapore.
One of the key initiatives for reducing the emissions associated with energy use on the project is to use electricity supplied from the national grid, rather than from diesel generators.
New Zealand’s electricity generation is mostly from renewable resources, so using energy from the grid reduces emissions by about 85%. To take advantage of this, the project has installed three transformers for site electricity. The first of these transformers powered the tunnel boring machine “Valerie” and has saved over 89,000 litres of diesel and avoided the release of 201 tCO2e of GHG emissions.
ENERGY EFFICIENCY AND CONSERVATION AUTHORITY (EECA) PARTNERSHIP
Not all activities can use grid electricity (yet!), so CRL has partnered with the Energy Efficiency and Conservation Authority to implement a driver training and truck monitoring programme for the haulage of the 200,000 tonnes of spoil coming out of the Albert Street trench.
The initial driver training course has been completed and shows potential for achieving valuable savings on diesel and associated emissions and cost.
One of the drivers, who had nearly 40 years’ experience and believed his driving to be very efficient, achieved an 8.2% reduction in fuel use over a 40km course.
Given the large quantities to be trucked, savings will be significant.
WATER / WAI
Saving water is also a priority for CRL.
As the design was refined from the base case reference design to the final detailed design, the team sought to reduce the amount of water that would be needed during operation of the CRL as well as during its construction.
To do this, projections of water use during construction were built up using information ranging from how many workers are expected to be on site, to how many trucks will need washing before driving onto Auckland’s roads.
Initiatives such as reducing water for wheel washing by loading trucks with long reach excavators, (rather than them driving into the muddy Albert Street trench), and recycling the water used in the CPO piling works, resulted in significant projected reductions for both contracts.
CONSTRUCTION WATER USE
Contract 1’s water use for the early part of the works is tracking below both the base case and detailed design projections. If this can be maintained as the more water-intensive piling activities commence, it will provide an excellent result.
Water use on Contract 2 has been greater than projected at this stage due to very high use between December and March, when additional water was needed to cool the cutting head of the tunnel boring machine used for the stormwater pipe replacement. However, if the C2 construction team continues the low water use of the last few months, valuable reductions compared to the base case can still be achieved.
Constructing a large piece of infrastructure such as the CRL requires significant quantities of materials - in particular concrete and steel - the production of which consumes valuable resources and produces greenhouse gases.
During the detailed design phase, the CRL design team sought to minimise this “embodied carbon”, and was able to reduce it by 1,800 tonnes of carbon dioxide equivalent (tCO2e): just over 5% of the total.
During the construction phase, the team has continued to look for ways to reduce the impact of its material use.
An approach identified during design to reduce the GHG emissions associated with concrete was to specify fly-ash, a waste product from coal-fired power stations, as a partial cement replacement.
With construction underway, data collected to date by contractor Connectus shows that specifying fly-ash for the 362 20-metre piles in Albert Street has reduced their GHG footprint by over 8%, saving approximately 122 tCO2e of GHG emissions.
50MM REINFORCING BAR
Changing the piling methodology underneath Britomart Station from contiguous piles to diaphragm walls contributed to an initial reduction in steel use during the design phase and also reduced the time and cost of the station underpinning.
However, due to the depth of the rock under the station (around 20m), using 40mm reinforcing bar (the largest size available in New Zealand) would have resulted in reinforcing bar “congestion”, preventing the concrete properly flowing around the bars to form the diaphragm wall.
Fewer, but larger, bars were therefore required. However, these had not been made previously in New Zealand. Contractor DSBJV worked with local manufacturer Pacific Steel in Otahuhu, which uses steel from the Glenbrook steel mill 40km east of Auckland, to fabricate New Zealand’s first 50mm reinforcing bar.
Besides improving constructability, using this larger diameter steel reduced the total weight of steel required by about 82 tonnes, lowering associated greenhouse gas emissions by just over 100 tCO2e.
It also reduced the transport emissions and costs associated with sourcing it offshore.