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4. Description of the Mt Eden Main Works
4.1 Overview
The Mt Eden main works will be undertaken from mid-2020 through to 2024. Construction works will occur concurrently along several active work fronts within the main works area to enable the redevelopment of the Mt Eden Station and CRL tie-ins to the NAL (refer to Error! Reference source n ot found.). In summary, the main activities include:
Set up of construction support areas (described in further detail in Section 4.5 below), including establishment of Industrial and Trade Activities; Ground improvements, in the form of deep soil mixing (contiguous piling and grout injection), within the NAL corridor between Mt Eden Road Bridge and Normanby Road; Construction of retaining walls and bulk excavations along the NAL to provide for the rail trenches and installation of new tracks. The excavation will encounter basalt, which will be removed via rock-breaking and blasting. In places, softer ground conditions are anticipated to be encountered, which may require the use of sheet piles; Construction of the eastern and western crossover structures that enable the CRL to tie-in to the NAL; Construction of the Porters Avenue and Fenton Street overbridges, and the public realm reinstatement of the surrounding area; Construction of the Normanby Road grade separation bridge, including regrading of Normanby Road and realigning the Boston Road roundabout; Construction of the Mt Eden Station, ventilation building, CRL platform and building foundations, and redevelopment of the existing NAL platform; and TBM operational activities, which include conveying spoil material from the tunnels, refuelling and general maintenance of the TBM.
A detailed description of the main works is included in the CEMP (Appendix D) and drawings depicting the main works are provided in Appendix F.
4.2 Staging
The main works are divided into several stages within the various work areas. Indicative dates and duration of the main construction activities have been provided in section 2.3 of the CEMP for each of the NAL geographical areas listed below:
East Facing Connection 1 (EFC1), i.e. Eastern tie in to Normanby Road; East Facing Connection 2(EFC2) from Normanby Road to Mt Eden Road, including eastern cross over structure; Mt Eden (MTN), including Mt Eden Station and Tunnels and NAL platform; and West Facing Connection (WFC) - including western crossover structure and western NAL. WFC is divided into two areas: WFC1 (from the MTN to just before Porters Avenue) and WFC2 between Porters Avenue and the western end of the NAL.
During construction, trains will utilise ‘Single Line Running’ (or SLR) when passing through Mt Eden in order to keep freight and passenger services operating on the western line while Mt Eden Station is closed. SLR will ensure enough space to safely complete construction on alternate sides of the rail corridor.
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Generally, the works along the NAL are divided into two stages to allow works on the northern (downmain) and southern (upmain) sections to correspond with the SLR of train services through the construction area. Stage 1 is generally on the southern side of the railway. Stage 2 is generally on the northern side of the railway. The staging drawings are attached in Appendix B of the CEMP (Appendix D). Some works are dependent on when full closure of a train line is undertaken (referred to as a Block of Line (BOL)). As an indication, the 2020 BOLs are as follows:
8-9 August 2020 (services investigation); 29-30 August 2020 (isolation of site and work on single line running); 12-13 September 2020 (disconnection of services from the platform); 26-27 September 2020 (demolition of footbridge); 24-26 October 2020 (footbridge piling between the two railway lines); Christmas 2020 (temporary sheet pile wall construction between MC10 and MC40).
Works within the Mt Eden Station area will occur in various stages. Early stages (i.e. between February 2020 and February 2021) have already been addressed in the Mt Eden Enabling Works outline plan package (refer section 2.1 of the CEMP (Appendix D)), and subsequent stages (i.e. from March 2021 to August 2022) will be undertaken as part of the main works. For the new Mt Eden Station building and ventilation building, construction of the foundations and building structures will be undertaken between March 2021 and August 2022, while the finishing of the buildings, public realm and landscape, will be completed as part of the future public realm reinstatement. These are illustrated in the staging drawings attached in Appendix B of the CEMP (Appendix D).
4.3 Vegetation Removal
The main works will require works in proximity to 34 trees, with 30 of these trees requiring removal as shown in Figure 4.1. More detail of the trees and vegetation within the Mt Eden main works area is provided in the TV DWP included as Appendix J of the CEMP (Appendix D).
A Flame tree (scheduled as a Notable Tree in the AUP) and a mature English Oak tree will not be removed as part of the main works and will be protected during construction (refer N1 and T24 in Figure 4.1). Works within the root zone of the Flame tree are however anticipated.
The method for tree removal will be informed by a qualified practitioner in accordance with site observations, such as the proximity of surrounding buildings, tree size and overall condition. Works will generally involve setting up fencing around the area of trees that require removal, trimming of branches and cutting of the trunk, excavation or grinding of the stump (dependant on location of network utilities) and subsequent clean-up of the work area.
Replacement planting will be undertaken as part of the public realm reinstatement on completion of the main works.
It is noted that a tree register has been developed identifying all trees and vegetation impacted and removed as part of the CRL project which will inform the mitigation planting plan.
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Figure 4-1: Trees within or near the main works area (Red circle – trees for removal/ Green Circle – trees retained)
4.4 Relocation of Network Utilities
Some of the network utility relocations within the Mt Eden area are being undertaken as part of the Mt Eden Enabling Works and the Normanby Road Early Works.
Additional relocation of network utilities is required to enable the Mt Eden Station trough, grade separation of Normanby Road and the NAL, and tie in works between CRL and the NAL. Works will include the relocation of stormwater, wastewater, potable water, gas, telecommunications and electrical utilities as outlined in Section 2.3 of the CEMP and shown in the General Arrangement Drawings in Appendix F of this Outline Plan. It is noted that the relocation of some utilities such as stormwater and wastewater services as per the construction staging, are permanent, whilst others may be temporary and reinstated upon completion (for example, at Normanby Road utilities will be diverted via the temporary services bridge, and following completion of the grade separation of Normanby Road and the NAL, these utilities will be incorporated into the new (permanent works) bridge or alongside and over the existing railway corridor).
Some utility relocations will also require works beyond the designation footprint. As explained in Section 1.4.7 of this Outline Plan, these works will be reviewed to ensure they are provided for either by the AUP as permitted activities, or additional resource consents would be sought as required. Currently there are no additional approvals required for minor utility works occurring outside of the designations.
All works relating to network utilities that are within or are in close proximity to the main works area will be managed in accordance with operational, safety and integrity requirements. Co-ordination and consultation with Network Utility Operators (NUO) has been undertaken throughout the development of the works methodology and will continue during the main works.
Further detail on the utility diversion works is included in the CEMP (Appendix D).
4.5 Construction Support Areas
There are three areas that have been identified as CSAs as part of the main works:
CSA 4, located between Ngahura Street, Nikau Street and Mt Eden Road
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Eastern Facing Connection CSA 5, located at 14-22 Boston Road, 11 Water Street and 28 Mt Eden Road; and Western Facing connection CSA 5, located near 1A Porters Avenue at the western end of the main works area.
CSA 4 and East Facing Connection CSA 5 have been established under the Mt Eden Enabling Works and Normanby Road Early Works Outline Plans.
The CSAs will be present throughout the majority of the main works duration, whereas site entry / exits / ACZs will be established and disestablished as required for related construction activities at different stages of the main works. Details on the access and egress to the CSAs and ACZs are provided in Section 4.4 of the TAP DWP (Appendix K of the CEMP).
4.5.1. Mt Eden CSA 4
CSA 4 has already been established as part of the Mt Eden Enabling Works, and provides space for the TBM plant and equipment, stockpile storage and handling area, concrete crusher, tower crane, and site office and associated facilities. The buildings and storage facilities to be placed on the site will be no greater in height, shape and bulk than the buildings that have been demolished. Taller structures such as cranes and a conveyor system will be temporary and removed following construction. Hoardings have been installed around the construction site, and general ‘housekeeping’ measures such as managing graffiti and litter will be enforced to mitigate the visual impacts on surrounding land uses.
The indicative site layout for the CSA 4 is shown in the staging drawings included as Appendix B of the CEMP (Appendix D).
4.5.2. Eastern Facing Connection CSA 5
Eastern Facing Connection CSA 5 is located at 14-22 Boston Road, 11 Water Street and 28 Mt Eden Road. The site has been initially established through the Normanby Road early works.
Main works activities within this CSA are expanded to include earthworks for the construction of the retaining wall in the north-eastern corner of the carpark (BST-01), the north sewer diversion and the establishment of site offices and staff facilities. This includes the establishment of carparking, stockpile and spoil areas and manoeuvring areas for heavy vehicles and machinery. An indicative site layout for the Eastern Facing Connection CSA5 is shown in the staging drawings included as Appendix B of the CEMP (Appendix D).
The CSA will be progressively established from February 2020 through to September 2020. Further detail of the CSA establishment is included in the CEMP (Appendix D).
4.5.3. Western Facing Connection CSA 5
Western Facing Connection CSA 5 is located at the western end of the NAL within the main works area, near 1A Porters Avenue. The site will be used to access the ACZ (between Porters Ave and the Dominion Road overpass), as well as for storage purposes by the piling team and bridge construction team. The existing pedestrian walkway will be blocked with a fence, and pedestrians will be diverted to a walkway under the bridge along New North Road. Western Facing Connection CSA 5 area has a steep slope and a block wall will be constructed across the entire site to contour the working area.
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4.6 Hours of Work
Construction work will generally be undertaken between 7am to 10pm Monday to Saturday, in accordance with the CRL construction noise and vibration standards (designation conditions 31 and 34). Piling and road cutting works will be restricted to 7am to 7pm from Monday to Saturday as per CRL designation condition 36.3b, except where a BOL results in the determination that the Best Practicable Option (BPO) is to undertake works on a Sunday due to Health and Safety requirements. This is will be addressed by a Site Specific Construction Noise and Vibration Management Plan.
Some construction works (e.g. concrete pours, traffic switches, deliveries, loading in/lifting, utilities work, D-wall works, confined space entries, road civil works, works occurring during the BOL) may be undertaken outside of these hours, however this would not be a general occurrence and will be done in accordance with the designation conditions.
Blasting in the vicinity of MediaWorks will take place Monday to Saturday at 10:32am and 2:32pm (as agreed with MediaWorks), and this will avoid MediaWorks sensitive times in accordance with designation conditions 32.6 and 35.11.
Some construction activities, such as tunnelling, will involve works between 10pm and 7am, i.e. night works. These activities will generally be completed below ground level and are anticipated to cause minimal disturbance.
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