Ground anchor installation for cable car access to remote SH3 construction site

Ground-breaking work on the Te Ara o Te Ata: Mt Messenger bypass.

Groundfix were appointed by the Mt Messenger Alliance to install multi strand ground anchors; to hold a 1.1 kilometre cableway allowing Waka Kotahi and its partners to start construction of the Te Ara o Te Ata: Mt Messenger Bypass.

Using a 28-metre-high central tower the cableway is designed to transport machinery and personnel safely over a 600-metre valley, into the heart of this remote project site, reducing the overall timeframe for construction. The cableway has the capacity to carry a 20 Tonne load and can lower items 60m below itself into the valley.

Due to the critical nature of these anchors an extensive testing programme of sacrificial trial anchors were completed well in advance of the permanent works. As there was limited historical data on ground strengths in the area (in particular in wet conditions), multiple different techniques were trialled. The weak mudstone rock is very sensitive when exposed to water resulting in a reduction in skin friction, so Groundfix proposed using an underreamer to “bell” out the borehole while drilling with water flush. This gave invaluable information to mitigate against the risk if groundwater was encountered during drilling.

The permanent works consisted of:

South Anchor Block:

• 6no 10×15.2mm multi strand anchors, 15m depth, 200mm diameter borehole
• Crane access only for machinery
• Drilling from temporary platform

North Anchor Block:

• 6no 11×15.2mm multi strand anchors, 18m depth, 200mm diameter borehole with 250mm underreams
• Helicopter access for all plant and materials
• Drilling from temporary platform
• 20 minutes bushwalk each way to access the worksite daily.

Te Ara o Te Ata has been described as an environmental project as well as a roading project. The Groundfix team takes a great deal of pride in how we have been able to achieve this – once in a lifetime – engineering feat yet limiting our impact on the environment. Tricky access to both anchor block sites, meant that crew had a 20 minute bushwalk each way to access the North Anchor block worksite along a scaffold boardwalk, and all drilling was carried out by temporary platforms and all plant and materials on the North Anchor delivered via helicopter.

Mirroring one of our core values of “outperforming expectations” Groundfix worked with global geotechnical suppliers DYWIDAG to implement cutting edge live monitoring technology with their smart anchor system. Powered by solar panels and using 4G data for communication, this system gives real time load readings providing data on the long term performance of the anchors and gives new and interesting insight as to how ground anchors perform against fluctuations in temperature, rainfall and cableway usage.

CAPABILITIES
Ground anchors & micropiles