Turitea Wind Farm

Geotechnical drilling, Anchor/Soil Nails, Heli-portable & Remote

2020

Manawatu, New Zealand

Electrix / Connell Contractors

96 – Post-tensioned DCP anchors
288 – Pull tests and post tensioning
2.8km – Furthest site from 4WD vehicle access.
1km – High tensile DCP anchors installed in 26 working days 1800 man hours with zero downtime and zero injuries

>4000 - Man hours (including testing)

As part of the $250 million Turitea Wind Farm project, Electrix was awarded the construction of a 12 km, 220 kV transmission line connecting the Turitea Wind Farm in the Manawatū–Whanganui region to an existing substation at Linton.

The line route crosses the hilly Tararua Ranges, requiring multiple turn-off points and, as a result, includes a number of support towers that function as strain structures.

Six of these support towers were to be excavated and constructed in rugged bush country within a reserve and municipal water catchment, requiring heli-portable operations.

From the outset of the project, the principal and contractor recognised that a critical, sensitive and challenging part of the project would be erecting the six towers located within the Turitea Reserve, the city’s water catchment area.

To avoid having to cut access tracks through the vegetation, helicopters were required to fly in all components and equipment needed for the foundation construction and tower assembly.

Webster Drilling was originally engaged to provide heli-portable and track-mounted geotechnical drilling services to inform the design of the tower foundations at each site, including two sacrificial test anchors installed and tested within the weak, fractured greywacke rock found across the route.

As a large portion of the multi-leg tower foundation mass would need to be achieved using rock anchors, the principal design engineer approached Webster Drilling to provide input on the constructability of the foundation design.

Over a number of months, we worked with the designers and main contractors to develop a methodology that balanced the physical foundation design, machinery requirements and health and safety considerations in the challenging terrain.

By the time the main contractor was ready to begin the foundation works, COVID-19 lockdowns and environmental consent processes had considerably delayed the six critical-path sites. The client was facing the possibility of the heli-portable tower erection falling within the region’s windiest season of spring.

To deliver the project as cost-effectively and quickly as possible, we recognised that several considerations were key.

High winds and low fog were the standout issues in terms of remaining on schedule, due to their potential impact on helicopter operations.

We recognised that the key to reducing our exposure to weather-related stand-downs was to engineer a drilling system that could be entirely self-supported, requiring no helicopter support for the duration of the works at a single tower foundation. This reduced our helicopter weather exposure to just six individual days required to complete all sites.

In conjunction with the design engineer, we designed and manufactured a custom frame that enabled the rig to be rotated about the centre of the tower foundation. This allowed the four anchors in each “foot” to be drilled precisely and efficiently, without the need for a large, heavy tracked anchoring rig to be flown in or the site to be enlarged to accommodate such a rig. We also made use of our custom-built hydraulic power units and two-piece heli-portable air compressors, which could be positioned in the centre of the site for the duration of the works and provide the power required to operate the lightweight man-portable rig.
A total of 7.5 km of 25 mm water lines was laid to the sites, eliminating the risk of running out of grout make-up and wash-down water during periods of bad weather. Our 500 L, twin-skinned heli-portable diesel tanks provided enough fuel to last for an entire tower site. Our large inventory of certified heli-portable baskets and pipe racks was used across the two crews, enabling all anchor bars, cement and consumables to be flown into the sites.

Two brand-new high-shear CM-160 heli-portable continuous grout mixers were also manufactured in our Engineering Workshop at short notice for the project.

Three personnel were immediately committed to the manufacture of 1,000 m of DCP pre-grouted anchor bars, which were on the project’s critical path. The first cured batch was delivered to site just two weeks after confirmation of the project go-ahead.

From job confirmation and materials order, WDE manufactured, mobilised and installed more than 1 km of pre-grouted, double-corrosion-protected anchors in just six weeks—all under remote, heli-portable access and extreme adverse weather conditions in one of the windiest parts of the world.

The client’s critical-path works were completed cost-effectively and efficiently, with zero downtime and zero injuries.