Since then TechSpan arches have been held in high regard by the mining industry.

TechSpan is a three-pin, two-piece, funicular curve-shaped arch that has been used for reclaim conveyor tunnels below coal and iron ore stockpiles.

RECO recently supervised the installation of a 130m precast concrete conveyor tunnel and a 180m transport drift tunnel for Rio Tinto's Kestrel coal mine in the Bowen Basin.

The company's involvement in the tunnel installations included the design and supply of precast TechSpan arches and associated precast concrete footing slabs.

"Rio Tinto was particularly interested in our total pre-cast option so we provided the base slabs in pre-cast format and delivered them and installed them," RECO operations manager James Bye told Australia's Mining Monthly.

The company designed the precast footing slabs to accommodate the variable foundations present over the length of the declining tunnels.

The footings needed to be particularly robust at the lowest depths, where the fill height above the arch reached 20m.

To allow practical transportation from the precasting facility of BB&D Constructions at Rockhampton, the footing widths needed to be limited to 1.1m with a weight of 25 tonnes.

"These precast arches are very highly detailed and very accurate, precise pieces," Bye said.

The grade and depth of the fills meant shear connections between arches and bases were necessary at lower depths in order to maintain longitudinal stability of the arch units.

"There were a few challenges involved in the installation," Bye said.

"These included the steepness of some of the slopes and the pre-cast slabs that were put down."

RECO used a crane to install the arch units with the arches placed directly opposite each other. Starting at the low end of the tunnel, the first unit was held in position on a temporary frame until the second, directly opposing, unit was positioned.

The completion of the two tunnels required RECO to use nine types of base slabs and 21 different arch types.