A unique underground mine tunnel scope, a tight schedule and demanding conformance specifications made the Havieron copper-gold exploration decline project in Western Australia as complex as it is necessary, according to Trimble distributor HL Geospatial.

To build the 2.5 km box cut decline tunnel, surveyors and operators were challenged to establish a technology-enabled workflow that would keep this project on track and within specification, the company said.

The Havieron copper-gold deposit is in the Paterson region of Western Australia. Through a joint venture, Greatland Gold and Newcrest Mining are looking to develop the deposit. The regulatory approvals for Havieron’s construction were provided at the end of 2020. Soon after, the joint venture was ready to begin construction. The large cylindrical deposit sits under about 450 m of sedimentary cover and the mineralisation extends over deep intervals to at least 600 m below the base of sedimentary cover, according to the jv.

The first phase of the underground mine development is the construction of a box cut, an approximately 2.5 km decline and associated surface infrastructure at the site to support an exploratory drill platform.

Mine Survey Plus, a mine surveying specialist, was contracted to provide continuous survey data and model-to-design comparisons to various stakeholders. The company has worked in more than 90-plus mines spanning nine different countries since its inception in mid-2017.

When asked about Havieron, Mine Survey Plus’s Senior Mine Surveyor, Justin Hearn, explained: “This is not a traditional hard-rock mine. It’s a soft-rock mine, which lends to a unique profile. Digging the decline tunnel is much like working a civil earthworks project as compared to a traditional drill-and-blast scenario in a hard-rock mine.”

To build the decline for the drill platform, crews must dig through the deposited materials, which has its challenges for both operators and surveyors. For operators, the challenge is to see as-built conditions as work is completed to ensure design conformance while digging through the soft materials. For surveyors, the challenge is to measure as-built conditions with speed and accuracy.

Scanning for opportunities

The Havieron decline profile is arched along the entire length to the footings, instead of the more conventional mining decline profile of square shape with a semi-arch rounded back for ground support. That custom profile requires a different setup – and for Mine Survey Plus some different technological capabilities, HL Geospatial says.

With help from HL Geospatial, a part of UPG Solutions, Mine Survey Plus had evaluated the Trimble® SX12 scanning total station.

Brett Grocock, Owner of Mine Survey Plus, said: “I trust and often call on HL Geospatial. Our success is at the forefront of their minds, and that’s reassuring – and the SX12 is just one example.”

Beneficial in underground applications, the SX12 scanning total station includes a small green laser spot (3-mm diameter electronic distance measurement (EDM) laser spot at 50 m), provides precise and clear set-out of tunnel construction points, and robotic technology to withstand the harshest conditions such as dust and moisture, according to Trimble.

In the case of the Havieron decline, Grocock noted: “We wanted the ability to check headings in real time. With this technology, we are able to do a complete setup and scan that is automatically georeferenced to the location.”

Real-time collaboration

To begin the Havieron decline construction, geotechnical engineers provided Mine Survey Plus surveyors a design profile for both excavation and the final shotcrete surface.

Hearn then used the Trimble Business Center Tunneling module to design the alignment. The resulting model is uploaded to the Trimble TSC7 controller with Trimble Access™ field software. Using the Trimble Access Tunnels module provides purpose-built tools for tunnel survey operations, according to the company.

Combined with the SX12 scanning total station, surveyors can automate the as-built data collection process and provide instant feedback to the excavator operators – typically one of the most time-consuming tasks in tunnel construction.

“We check the excavated profile using the Tunnel Auto Scan Function, and then scan existing conditions with the SX12 scanning total station at various cuts along the face,” Hearn said. “The scan data is then compared against the design profiles to verify conformance – all while in the field. We don’t need to take data into the office for verification; we can do it live.”

Access to data in the field has been hugely appreciated by the machine operators who are used to seeing a straight-line conformance check, according to HL Geospatial. The 3D scan provides an added layer of visual communication and immediate feedback on any course correction that may be needed.

“In the early stages, we were all – surveyors and operators – getting used to the different methodology and profile style,” Hearn noted. “With the conformance comparisons on the controller, the operators can visually see where they might need to do a little more work. Many times, they are standing next to me checking their work. They love that we’re able to give them near real-time feedback in the field. It’s a whole new concept in this realm. We’ve seen greater turnaround and increased precision in a very short time because of the in-the-field visuals.”

The engineering team is also taking advantage of the scan data. Hearn added: “They’re looking at our data showing the different strata as a way to confirm the initial geological model and verify the design. Essentially, they’re using our scans to create a better model of the area.”

Mine Survey Plus is also using Trimble Access’ Continuous Topo feature to conduct a regular pickup. The Job XML file is imported into Trimble Business Center for a visual comparison against the tunnel alignment, while the string data is imported into Deswik, a CAD program for mining applications.

Heran said: “With the latest release of Trimble Access, I am looking to utilise the Half Dome Scan with LAS exporter and Scan to Surface functionality, with the eventual goal of using the scan data alone to generate the 3D models in Deswik.”

Meanwhile, Hearn and Grocock continue to support the Havieron decline construction, which is currently on track for completion in 2023.

As of July 2022, Greatland Gold reported the decline construction has advanced 489 m, with 111.5 m since the last report a month prior. The progress reflects the highest daily advancement rate during a single reporting period since commencement of the exploration decline.

Shaun Day, Managing Director of Greatland Gold, said: “The observed acceleration of the decline advancement is particularly pleasing. The improved advancement productivity is consistent with the expected improvement of ground conditions with depth.”