Client: Waikato District Council

Location: Waikaretu Valley Road

Date: June – August 2024

 

CONTEXT

Base Civil Limited was engaged by Waikato District Council to deliver emergency slip repair works on Waikaretu Valley Road following slope instability and pavement failure at two locations. The purpose of the project was to stabilise the road corridor, reinstate the pavement, and restore long-term resilience and safety to this rural transport route.

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CHALLENGES

Project challenges included steep terrain, limited working space, and the need to maintain traffic access throughout construction.

TRAFFIC MANAGEMENT

Temporary traffic management was maintained for the duration of the works to ensure the safety of road users, site personnel, and adjacent landowners.

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ENVIRONMENTAL MANAGEMENT

Environmental management measures included erosion and sediment controls appropriate to the rural and steep nature of the site.

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PROJECT MANAGEMENT

Base Civil undertook full site establishment and management for the project, including services location, site set-out, all quality assurance requirements, contractor programming, regular reporting, and as-built documentation in accordance with WDC requirements.

 

EARTHWORKS

Earthworks included site clearance, removal of failed material, excavation and benching for gabion wall construction, and cut-to-waste of unsuitable material. Where poor ground conditions were encountered, unsuitable subgrade was undercut and replaced with engineered hardfill. GAP65 material was used behind the retaining structures to ensure stability of the repaired embankments.

 

EMBANKMENT STABILISATION

The core element of the project involved the placement of rock-filled, stainless steel gabion baskets in stepped layers. Foundations were constructed using compacted GAP65 and - where required due to bedrock conditions - mass concrete foundations. Geotextile filter fabric and drainage composite were installed behind the gabion walls, along with rip-rap erosion protection at outlets, and batter slopes to manage surface water and prevent scour.

 

DRAINAGE

Comprehensive drainage works were completed as part of the project to reduce future slip risk. This included the installation of 110mm perforated and non-perforated subsoil drains, subsoil flushing eyes, and energy dissipaters at outlet locations. Base Civil also completed approved variations to extend subsoil and stormwater pipework beyond the road corridor into adjacent land to improve overall drainage performance and discharge control.

 

PAVEMENT AND SURFACING

Following the structural works, Base Civil reinstated the road pavement by saw cutting existing surfaces, preparing and compacting the subgrade, and constructing new pavement layers. This included a 250mm GAP65 subbase, a 110mm AP40 basecourse, and a two-coat chipseal surfacing to match the existing road. Smooth pavement tie-ins were achieved to ensure a safe and durable driving surface.

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LANDSCAPING AND REINSTATEMENT

Landscaping and reinstatement works were completed on all disturbed areas, including topsoil replacement and hydroseeding of batters to stabilise slopes and reinstate the surrounding environment. Additional works included the installation of mountable kerb and channel where required, new white-painted timber sight rails, multi-wire farm fencing, edge marker posts, and pavement line marking.

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RELEVANCE

The project was delivered within the agreed construction programme over 48 days, allowing for wet weather delays. This project demonstrates Base Civil’s capability to deliver emergency road repairs, gabion retaining structures, drainage works, and pavement reinstatement in a challenging rural environment.