Woodsmith Mine has been called the biggest mining project in Britain in decades. Even in the world of mining, where scrutiny can be intense, this is possibly our most high-profile project to date. Sirius Minerals contracted DMC to sink four shafts to access and develop the world’s largest and highest-grade ore body of polyhalite, a valuable fertilizer. The two main shafts at Woodsmith Mine will be the deepest commercial mineshafts in the U.K. and Europe.
Woodsmith Mine is situated in the North York Moors National Park, near the historic town of Whitby and a Royal Air Force Base, so there are numerous restrictions on noise, lighting, building size, water discharge, and vehicle traffic. Our client has a strict schedule that needs to be met. Sinking record-setting mineshafts amidst these challenges is difficult, requiring innovation, expertise, and caution.
We don’t think it’s an overstatement to consider this project the future of mining. Large commercial mines are rarely set up near towns and, in the West, never in protected areas. Woodsmith Mine will set a precedent for mining projects in sensitive environments. DMC is committed to a responsible approach, seeking and executing the best possible solutions.
As the main shafts at Woodsmith are subject to significant operational restrictions, we focused on ensuring a flawless approach. The production shaft will reach a depth of 1594 meters, and the service shaft will reach 1565 meters, both with a diameter of 6.75 meters. Two additional shafts will be sunk to 360 meters to enable the construction of the 37 kilometer material transport tunnel, which will be the second longest tunnel in the U.K, behind the Channel Tunnel.
We are applying our experience in innovative engineering to optimize the boring machine and shaft lining to suit the geological conditions of the area, which will allow the mineshaft to last 100 years. The main shafts will have headframes situated in the ground to reduce building height. Shaft spoil removal and ventilation systems, as well as all mining services such as compressed air and communications, are also being designed by DMC and will be installed as the shaft is sunk.
Sinking the main shafts efficiently and safely is our key priority, so we chose to use two Herrenknecht Shaft Boring Roadheaders (SBR). The SBR is a 60 meter tall suspended shaft sinking machine, with 12 work decks and 2 service platforms. A telescoping, boom-mounted cutting head is used to precisely excavate rock via a partial-face cutting method. The cutting head works in a cycle, starting each cut from shaft centre to shaft wall, repeating until a layer of material is removed. Excavation proceeds in 1 meter increments, followed by SBR lowering sequences.
The SBR was chosen over conventional drill and blasting method due to its advantages in improving safety and schedule. This methodology will allow us to satisfy several operational objectives, moving away from the use of explosives and providing a safer more predictable work method. Instead of a linear process, the SBR allows work to be completed concurrently as the shaft is sunk, as well as minimizing damage to exposed host rock, and further improving safety while minimizing downtime. Work decks above the cutting head allow workers to install shaft lining and tubbing as excavation continues, while a pneumatic mucking system (PNM) removes waste rock.
The machines to be used at Woodsmith Mine are next-generation of the SBR technology, improved based on our experience from the two completed SBR shafts in Saskatchewan, Canada. Cutting head power has been increased by 600 kW. Stabilization has been improved, which speeds up the lowering sequence. The PNM has also been improved, with better dust filtering and simpler muck removal that allows simultaneous movement of materials and manpower. All attachments for the SBR have also been redesigned for quick installation and removal, and all components are more accessible. Finally, a detachable second service platform has been added so the SBR can remain in place while operations are carried out higher in the shaft.
With ore access set to occur in 2021, Woodsmith Mine is dependent on timely shaft sinking. We have the expertise and equipment to ensure milestones are met safely and efficiently – as well, we are working diligently and hope to improve our client’s schedule by up to 6 months. The SBR allows continuous work on a number of fronts, improves shaft sinking rate, and makes operations as safe as possible by removing workers from the excavation chamber, allowing smooth shift transitions, minimizing repair downtime, and eliminating the need for blasting.
Our approach, which we share with Sirius Minerals, is to make Woodsmith Mine a true example of responsible mining. By carefully considering each step and applying best-in-class technology, innovative engineering, and quality construction, we can ensure that the best solutions are being applied to make the project a resounding success. In this case, that means meeting safety and environmental responsibilities while ensuring a rapid pace of work to meet project milestones.