Designed, supplied and supervised by RECO, construction work started in January and was completed by May, with the conveyor tunnel 130m long and the drift tunnel 180m long.
RECO started manufacturing the tunnel components in August last year, which consisted of specially designed precast TechSpan arches and associated precast concrete footing slabs.
“The precast footing slabs were designed to accommodate the variable foundations over the length of the declining tunnels,” RECO said.
The company said the footings slabs had to be particularly robust at the lowest depths, where the fill height above the arch was 20m.
“At this depth, footing widths needed to be limited to 1.1m and the weight to 25 tonnes to allow practical transport from the precasting facility at Rockhampton.
“As the height of fill reduces nearing the tunnel entrance, the base slab design changed until a minimum fill height of 2.75m was reached.”
RECO engineering manager Chris Lawson added, “The combination of grade and depth of fills also meant shear connections between arches and bases were necessary at lower depths to maintain the longitudinal stability of the arch units.
“The shear connectors prevented the narrow arch units from rotating due to the steep grade.”
RECO operation manager James Bye said the arch units were installed using one crane, 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 to fully engage with the first unit,” he said.
“Once both units were adjusted for position, the form was lowered and the units were then fully self-supporting. After four sets of units were installed, the form was repositioned up hill and the process repeated.”
Nine different types of base slab and 21 different arch types were used for the two tunnels.
Kestrel update
An RTCA spokesperson told International Longwall News the Kestrel Mine Extension project remained on track to meet its first scheduled coal in 2012.
“Work on the Kestrel Mine Extension was altered in January to enable Rio Tinto Coal Australia to optimise cash efficiencies and make better use of in-house expertise,” the spokesperson said.
“There is no suggestion that any of the jobs on the project are on hold.”
The KME project aims to lift production to 5.7 million tonnes per annum from 2012, extend the mine life to 2031, increase the longwall face width to 375m and create up to 250 jobs in the construction process.
In January, RTCA announced it would cut 2009 production by 15%.
“This step was taken for the foreseeable future, until such time as sales improve,” the spokesperson said.
Macquarie analysts are expecting to see idled mining capacity switched on again in the second half of this year on the back of increasing Chinese coking coal demand.
Macarthur Coal recently said it had shipped a number of cargoes of low-volatile pulverised coal injection coal and thermal coal to China for the first time in the company’s history.
“While the data is inconsistent, the anecdotal evidence is very strong as sales of metallurgical coal to China have increased significantly over the calendar year,” Macarthur said in a presentation at the UBS Annual Resources Conference.
Macquarie has forecast premium hard coking coal to reach $US140 a tonne next year in benchmark contracts.
