The Wellington Cable Car has been in operation since 1902 and carries over 1,000,000 passengers per year from Lambton Quay to the top of the Botanical Gardens and the suburb of Kelburn.  It is an iconic tourist destination as well as a commuter means to get ‘up the hill’ and gain a panoramic view of the harbour and city.

The cable car track is 785m in length, rising about 120m in elevation.  It passes through 3 tunnels and over 3 bridge structures.  The upper portal wall of the middle tunnel is approximately 9m in height which is connected to a retaining wall at a perpendicular alignment.  Geotechnical assessments were carried out and WSP Consultants identified these walls of the middle tunnel at risk of failure/collapse under earthquake loading. 

Wellington Cable Car Limited (WCCL) is responsible for operating the Wellington Cable Car and maintaining the cable car assets and facilities.  Following a tender process WCCL awarded the contract to Contech for the strengthening of the portal and retaining walls in early 2022.   

The scope of work included: 

• Installation of four Proof Anchors to be load-tested until failure 

• Installation of production anchors (double-corrosion protected 40mm Macalloy bar) including post-grouting and load-testing (suitability and acceptance testing) 

• Concrete repairs and plastering to both retaining and portal walls 

• Application of coating systems (painting and anti-graffiti) 

• Installation of drainage systems 

The location of the worksite was very restricted, and is bordered by an adjacent road and Victoria University’s University Hall of Residence.  The portal and retaining walls support steep slopes with limited access points to them, making lifting and moving heavy equipment on site very challenging. 

Due to the proximity of the accommodation buildings, pre- and post-condition surveys and weekly monitoring was required to confirm no detrimental effects were sustained during the construction phase.  Coordination with many parties was a critical component of managing this project including WCCL, Wellington City Council, Victoria University, appointed Heritage Advisor, and neighbouring properties including University Halls of Residence.  Coordinating the work above the live cable car operations, and traffic control on the road (including a limited number of road-closures) was required to undertake the strengthening works. 

Due to the significance of the Cable Car to Wellington City, special consideration was required in undertaking the strengthening and remedial works.  This included a Heritage Consultant to observe and advise on the workmanship and surface finishing of the walls, with particular attention to the voussoir.  

Consideration of the neighbouring University Halls of Residence adjacent to the site prompted additional measures to ensure disruption to the buildings and students (especially during study periods) was minimised.  This included sequencing works around sensitive exam times, weekly inspections and communication with Halls staff and strict control of noise, vibration and dust. 

All site works including scaffold installation, drilling, anchoring and load testing had to be caried out above the operational Cable Car line.  This meant some operations needed to be completed at night after the last cable car run for the day. 

During construction, very poor ground conditions were encountered which led to difficulties during the drilling/anchoring process.  Difficulties were also encountered with the existing wall which was discovered to be of poorer quality than expected, and additional remedial work was required at areas of poor condition. 

Remedial work, and plastering of the concrete walls was undertaken to approved methodologies with the Heritage Consultant providing guidance and advice on techniques, finished surfaces and painting.