Among Northern Yorkshire’s Moors Sirius Minerals is constructing its deep potash mine, electing to tunnel its transportation system. The TBM launch shaft requires a total depth of 360m through the local geology consisting mainly of Redcar Mudstone. But the shafts have had to go through sandstone and an aquifer.
Herrenknecht provided a vertical shaft sinking machine (VSM), which excavated to a 115m depth on the access shaft, setting a world record (previous record, 84m). The VSM allowed the sinking of the shafts through near-surface water aquifers, due to the fact that the machine is designed to work underwater with a shaft lining being lowered behind.
A spokesperson for subcontractor Joseph Gallagher explained that “typically, shaft lining would be created from pre-cast concrete segments but, in conjunction with contractors Careys Civil Engineering and Joseph Gallagher Limited, Sirius utilised a new ‘slip form’ technique to pour the concrete lining. Using this technique, by continuously pouring the shaft walls simultaneously with the VSM’s excavation activity, the team was able to line the shaft more safely, rapidly and cost-effectively.”
Site personnel spoke to Tunnels and Tunnelling in April about the VSM and said, “Grouting has a 95 per cent success rate, and you are not always sure how long to leave for the process. With the VSM, there is no need for piling or d-walling. It gave us a level of certainty in the schedule and of the protection given to the local aquifers.”
The crew then used traditional techniques to continue excavation of the shaft to the full depth.
Equipment, technology and knowledge sharing between tunnelling and mining are increasingly present as both industries face deeper project and more complex geology.
Organized by the Canadian Institute of Mining, Metallurgy and Petroleum, in conjunction with the UK’s Institute of Materials, Minerals and Mining, North American tunnellers and miners can take part in a global shaft conference this autumn in Toronto. Targeting shaft designers, constructors, equipment suppliers and mine owners, the event has included a focus on tunnelling from its inception in 1959.
Topics will include sinking equipment and methodology of the future, shaft support and liner design, mechanical cutting of shafts and raise boring, safety in design and construction and case studies in both design and construction. With three days of presentations and a keynote by Bill Shaver (of Redpath, Dynatec and DMC), among other speakers, there is likely plenty of overlap with tunneling.
