Development of a hard rock tunnel alignment laser

In 1971 and 1972 I worked with the team who developed an alignment laser for hard-rock tunnelling. The use of lasers is now standard practice in mine surveying but was challenging at the time. The only lasers available at reasonable cost were laboratory models with limited range, which could not withstand the dust, humidity and blasting vibrations in a tunnel.

The work was done by the survey department at New Broken Hill Consolidated Limited (NBHC), then the most southern mine on the Broken Hill field. A new ventilation shaft (No 3 airway) was being developed well south of the main shaft, so there was a need to complete a long drive on each of the main levels to connect with the new shaft. The tunnelling would be done using compressed-air powered jumbo drills mounted on rail carriers, with compressed-air powered boggers and battery-electric locomotives hauling rail cars.

Tunnel alignment surveying was a difficult task. The tunnelling crew worked to a cycle that fitted activities into a working shift and did not encourage interruption by the surveyors, who nevertheless had to carry an accurate survey up to near the tunnel face and then provided marks that the miners could use to align the drill jumbo for blasting each round. If the marks were paint lines on the backs (roof) of the tunnel then they needed to be extended at least every second round. If the marks were two hanging wires on which the miners could hang plumbobs, then they might serve for four or five rounds before new ones were required closer to the face. Either way, grade-marks were also required, and these were usually painted on wall of the tunnel to keep it rising at the designed one percent grade.

This process could be replaced by a laser mounted in the tunnel, which was expected to keep the tunnel on line and on grade for several hundred metres before it would need to be moved forward. To do this, a standard laser would need to be protected for the environment in a casing which allowed accurate alignment and it would need a collimator, or lens assembly, to focus the laser beam at a distance.

The helium-neon (He-Ne) gas laser was invented in late 1960 and was the first continuous beam laser. Only six years later a He-Ne gas laser was first used underground to guide a tunnel boring machine at the US Bureau of Reclamation’s Navajo Indian Irrigation Project near Farmington in New Mexico. The Perkin Elmer model 5620 construction laser became available in 1967 and the use of lasers quickly spread in US mines, but the machine was seen as too expensive in Australian dollars.

The prototype laser at NBHC was designed by George Dalby, the Chief Surveyor, with drawings prepared by Mick Pollock, the Survey Draftsman. The senior surveyors also contributed ideas. A laboratory helium-neon gas laser was obtained from Quentron Optics in Adelaide. As supplied, this was a glass laser tube mounted inside a lightweight rectangular blue aluminium casing, which also contained the power supply. The laser beam emerged from a small hole in the front; at the rear was an on-off toggle switch and a power cord. The unit was about 700 mm long, 150 mm high and 75 mm wide.

The unit was disassembled and the new housing designed. This was an aluminium tube about 10 mm thick, 700 mm long and 150 mm in diameter. At the front an adaptor plate allowed a collimator, which looked like the telephoto lens from a camera, to be screwed on. Inside were soft mountings for the laser tube. At the centre of the rear plate was a 25 mm cube on which the adjusting screws would bear.

Most of the manufacturing was done by the mine’s machine shop, with some final work by Cyril Clare, a fitter who worked alone with two lathes and other machines in the Rock Mechanics Laboratory. There was a heavy base plate on which two rings which comprised a set of sturdy and complicated gimbals were clamped around the front of the laser unit. At the rear, four opposing set screws allowed it to be adjusted in both planes. All of the work was done to a precision like that of a theodolite, although the parts were heavier and stronger. The electronics were housed in a separate box.

Once manufacture was completed, the unit was checked by taking it up into the No 3 Airway head frame and projecting the beam onto to the concrete side of the main shaft head frame. Using walkie-talkies, surveyor Trevor Hannigan and I were able to stabilize and focus the beam, after which we drove to the main shaft and rode the elevator up to the top of the head frame to admire the dancing red dot. George Dalby had been called in from a local hotel to see the result and was a little unsteady as he leaned over the parapet.

The site chosen for the first trial was the west exploration drive on 21 level. The 21 level was developed in the late 1960s and a high-speed development was needed to connect the level to the Zinc Corporation mine immediately to the north. New equipment obtained for this development included a twin-boom rail jumbo and a set of Hagglunds shuttlecars. These were long rail cars that fitted into each other and had a chain flight conveyor on the floor. Broken rock was loaded in from the face at one end and was conveyed all the way through the train, so there was no need for shuffling trucks up and down the line to put an empty on behind the loader.

The new technology proved disappointing. The union insisted that it’s “two men one machine” rule applied per rock drill, and as there were two booms on the jumbo, it had to have four operators. The Shuttlecars were difficult to unload at the ore pass tip and required a lot of maintenance. Despite the problems, under the leadership of Tony Brown the mining crew achieved very good advance rates. Trevor Hannigan was the surveyor responsible for this project and I was his assistant, though later I took over as 21 level surveyor. We worked hard maintaining the alignment until the drive broke through to the Zinc Corporation, then had to survey a new west exploration crosscut from it, which was to provide exploration access to the Western Mineralisation target that was thought might be the future of the mine (and later, the Broken Hill field). We hoped the new laser would make our jobs much easier.

We designed a place for the laser at the end of the long curve where the north drive branched off into the west crosscut. A chamber was excavated at the north side on the edge of the crosscut, and a very solid concrete plinth was built on which the laser would sit. There was enough space to walk around the plinth to adjust the laser as necessary. It took several weeks for excavation and concrete works to be completed. The laser was mounted on the plinth and covered by a strong steel box with a hinged flap where the beam emerged. Once installed, the laser worked as expected and provided a reference spot on the face of the tunnel from which the blasting pattern could be laid out. Initially a surveyor had to turn the laser on and off; later the miners were allowed to do this. The safety aspect of possible eye injury from looking back into the laser beam was well recognised, so the laser beam was 2.06 metres (6 feet 9 inches) above rail level.

As the tunnel face got further away, a point was reached where the laser spot was too large and it danced about on the face, at which point the laser unit was moved up. Each installation was made progressively simpler until it was a steel bracket bolted to the tunnel wall. Early on, a means of checking the laser alignment was required. A steel flap with a hole in it was hung 30 metres ahead of the laser unit, with the idea that if the beam passed through the hole then it was still on line. However, the hole acted as a pinhole lens and diffracted the beam into a series of concentric rings, making it useless. The flap was changed to a target that could be swung down periodically as a check. Later, when the tunnel had to turn a corner, a specially machined prism was used to turn the beam onto the new alignment. This experience taught us that it was easier to relocate the laser unit.

The second laser unit, installed in the 15 level south drive, was much simplified. Instead of gimbals the front of the tube was clamped in an O ring that provided enough flexibility for directional adjustment. The installation was uneventful, and the use of lasers became standard practice. I don’t remember much of my own minor role in this story, though I do remember dismantling the laboratory laser and discussing designs with Cyril the fitter. At some point I was offered a job by Quentron Optics, which suggests that they were impressed by whatever I had contributed, but I decided to stay with the mine and complete my engineering studies.

Mount Isa Mines Limited was a very innovative company and we usually found that their work led or paralleled ours in the early seventies. MIM first used a survey laser in 1969.

Reference: ZC/NBHC in-house magazine Ore Bits Friday 28 April 1972

The author in 1972, showing how centre lines were painted, in this case for installation of rails at the shaft

An NBHC survey crew performing a check survey in 1972 with a Wild T2 theodolite.

Trevor Hannigan, Leigh Clifford and Oliver Messenger. Trevor, Oliver and the author were trainee engineers.

Leigh was a newly arrived engineer on a short orientation secondment to the survey department. Photo by the author.