Whaka
terrace

HGM were engaged by Higgins to complete a retaining and road reinstatement project at Whaka Terrace on behalf of Christchurch City Council following a significant slip in 2021. The slip caused extensive damage to the road and deposited a large volume of debris into a neighboring property below, creating safety concerns and a need for a long-term stabilisation solution.

HGM had previously been engaged directly by Christchurch City Council immediately after the landslip to remove the debris from the affected property. This early involvement provided our team with a thorough understanding of the site’s challenging ground conditions, enabling us to contribute valuable expertise during the Early Contractor Involvement (ECI) phase. Working alongside Higgins and the design team, we assisted in developing practical construction methodologies and solutions that addressed the site’s complex geotechnical constraints.

Scope of works

Excavation for the temporary works which entailed an anchor/ shotcrete face to 3 sides of the slip to support the road during construction
Design and implementation of a temporary works platform to allow access for the piling.
Installation of 14 reinforced concrete piles, each approximately 14 metres deep and 600mm in diameter, socketed four metres into competent rock.
Construction of a reinforced concrete capping beam.
Construction of a MSE wall with back fill up to road level with a gabion facing.
Construction of a reinforced concrete capping to the MSE wall .

Challenges & Solutions

The project presented significant logistical and engineering challenges. The steep terrain, limited working space, active traffic lane adjacent to the work zone, and close proximity of neighbouring properties required careful planning to ensure both safety and construction efficiency.

A key challenge was providing suitable access for the piling rig on the unstable hillside. HGM developed an innovative temporary works solution by designing and constructing a lift-in working platform that provided a stable and safe operating surface for the piling equipment. Once the reinforced concrete piles had been completed, the platform was removed, allowing construction of the MSE retaining wall to proceed without obstruction. This staged approach minimised risk, maintained site safety, and enabled construction to progress efficiently despite the difficult conditions.

Project Delivery

The complex engineered solution incorporated multiple structural and geotechnical elements, requiring close collaboration between HGM, Higgins, Structural and Geotech Engineers, and Christchurch City Council throughout the project. Working as a specialist subcontractor, HGM maintained a strong focus on quality assurance, environmental management, and programme delivery while coordinating the complex sequence of works.

The project was successfully completed on schedule, within the original budget, and with zero safety incidents, delivering a resilient long-term solution that restored two way road access and stabilised the hillside for the future.

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Location

Whaka Terrace, Huntsbury, Christchurch

Client

Higgins

Date

2025 / 2026

Aerial view of excavation, retaining walls and civil construction machinery working along a narrow hillside road. The project shows detailed site preparation, project management and site construction for a complex slope retention project.

Civil construction machinery working beside a residential hillside site with retaining walls, scaffolding and safety barriers in place. The image shows excavation, structure construction and project management on a complex construction project.

Civil construction workers carrying out excavation and retaining walls work beside a concrete structure on a steep residential site. The project shows specialist site construction, drilling services and slope retention work being completed by experienced civil contractors in New Zealand.

Civil contractors working below a construction drill on a steep excavation site for retaining walls and slope retention. The image shows specialist drilling services, rock anchors and concrete structure work forming part of a complex construction project.

Crane lifting equipment for retaining walls and civil construction work on a narrow hillside site with scaffolding and safety fencing. The project involves excavation, slope retention and structure construction completed by skilled civil contractors.

Civil construction crew installing steel reinforcement beside excavation works for a retaining walls and concrete structure project. The image shows site contractors completing foundation construction, slope retention and detailed site preparation in a confined area.

Civil construction worker overseeing sling operations as a concrete structure component is lifted beside excavation machinery. The image highlights retaining walls work, construction drill access and site contractors managing a complex construction project.

Construction worker guiding a suspended concrete section during sling operations on a retaining walls and civil construction site. The work shows careful project management, site construction and utility infrastructure support in a confined hillside location.

Excavator being lifted by crane truck during sling operations for access to a restricted civil construction site. The image shows machinery transport, site preparation and project management for retaining walls and excavation works.

Aerial view of a civil construction site with excavation, retaining walls and machinery working alongside a hillside residential area. The project demonstrates project management, siteworks and complex construction projects delivered by civil works contractors.

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Large scale retaining walls and gabion baskets forming a reinforced concrete structure beside a steep accessway. This civil construction project includes siteworks, ground stabilisation and slope retention as part of a complex construction project.

Completed retaining walls and civil construction works supporting a hillside residential development in Christchurch. The site shows project management, siteworks and foundation construction completed by HGM Construction, civil contractors in New Zealand.

Completed retaining walls with gabion baskets and concrete structure elements supporting a steep accessway. This civil construction project demonstrates slope retention, ground stabilisation and siteworks completed by specialist civil contractors in New Zealand.

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