HEB Construction Ltd was appointed Main Contractor for the contract which involved rock-bolting, rock fall mesh and reinstatement of 300m of lakeside road. Ancor Loc Earth Systems Ltd was awarded the package to carry out the rock scaling and abseiling works, rock-bolting and rock fall prevention, which comprised the majority of the contract works.
The site presented a degree of difficulties with its historical significance to local iwi and extremely environmentally sensitive, being on the shores of Lake Rotoiti. The site itself was a treacherous, undulating, out-cropping rocky face which posed risks of large falling rocks and debris. The road had previously been reduced to a single lane of traffic, controlled by traffic lights and was subject to constant falling debris, some rocks as large as a mid-sized family car.
Upon review of the site conditions, it was deemed that using the traditional abseiling rigs and techniques to install the rock-bolts was too time-consuming and not feasible given the tight construction programme. It was expected that such rigs would only be capable of one-two rock anchors per day, whereas the targets were far greater.
By combining our experience, technical knowledge and creativity, Ancor Loc Earth Systems Ltd constructed two crane basket drilling rigs, which are believed to be a first in New Zealand for use on a civil construction site.
These were designed and developed in-house by our technical department. The use of these baskets meant our experienced drilling operators were able to carry out the rock anchoring works to a high level of productivity and standard. Suspended from mobile cranes, the baskets provided a firm, stable platform, sheltered from the sun, wind and rain and meant that up to fourteen rock anchors could be installed, per rig, per day.
In total some 600 rock anchors were installed, tested and locked off at their required loads. Three types of rock bolts were required, with loads ranging from 200kN to 400kN. Williams All-Thread-Rebar was the preferred solution for anchor tendons, as the wide range of sizes could be matched to suit the required loadings. Due to the tombstone-like formation of the rock, grout loss became a major issue. Some 1.4 million litres of grout was pumped into the rock-face, with the final one hundred anchors re-drilled to a greater depth and utilising Williams grout socks.
Throughout the project the priority was re-opening the road to two lanes of traffic in time for the summer period and busy season. However it was no small task due to the tricky terrain and unfavourable ground conditions. The severe loss of grout meant that the project was delayed and the Christmas target was not met. However Ancor Loc Earth Systems Ltd, together with HEB Construction, continued to push the envelope in terms of resources, labour and plant used throughout the contract to maintain the programme as much as possible. The end result was a delay that was thought to be very minimal considering the impact the delays could have had.
Upon completion the stats speak for themselves:
- 20,000 man hours worked
- 590 No. rock anchors installed, a total of 3162 lineal metres
- 5,200m2 Rock Mesh installed
- 1,386,657 litres of grout pumped
- 0 lost time incidents/injuries – yes zero!
- 0 environmental issues
- Awarded the highest level of compliance for Safety by HEB Construction
Ancor Loc Earth Systems Ltd are proud to have been involved with another landmark project. The entire project team, from HEB Construction, Opus International Consultants and Rotorua District Council worked hard and closely as a team to bring another successful project over the line.