Wilton Enabling Works

Sirius Minerals is constructing a large polyhalite mine at Woodsmith, near Whitby. The polyhalite will be mined at Woodsmith and then transported via a 37km long tunnel to the Wilton International facility in Redcar, to be granulated and prepared for export.

Tunnelling works are being undertaken by STRABAG, with MGL Group (Rainton Construction, MGL Demolition and MGL Earthworks) being awarded significant work packages, including the installation of a large pile-mat with associated drainage.

MGL Earthworks was heavily involved in the design of the works in liaison with STRABAG. Initially this specialist work related to site logistics, but it quickly increased to assisting STRABAG in calculating the optimal position and site level for the following elements, including (but not limited to):

• 12,500 m² multi-tiered pile mat
• 5,000 m² segment factory
• 50,000 m² segment storage slab
• 200,000 m² MHF platform
• 3km of permanent and temporary roads
• Construction of three large ponds for surface water management
• Management of all SCL tunnel arisings

The MGL Earthworks team also undertook the following works under significant time and quality restraints:

• Excavation and stockpiling of 180,000 m³ of topsoil, including the testing, and remediation of 6 asbestos hotspots within the soil
• Excavation and stockpile of 80,000 m³ of surplus clay/mudstone
• Excavation, classification, testing and placement of 35,000 m³ as structural fill
• Import of 120,000t of aggregate
• 1,000+ separate earthworks tests including a wide range of geotechnical and chemical issues

We also undertook significant mudstone compaction trials with the appointed Consultants from Sirius Minerals and STRABAG. By processing and testing existing mudstone to replicate the Tunnel Boring Machine (TBM) arisings, we were able to undertake significant geotechnical and chemical testing to assess the material for future re-use.

During the works it became apparent that a large volume of buried slabs, foundations and service corridors were present. We proposed a remediation and recycling strategy (via materials management) that meant 6,000t of material was processed into re-useable earthworks materials, saving on both export and import costs. This was done utilising BRE SmartWaste as a key sustainability reporting tool.

We were awarded the haulage and stockpile of the mudstone generated by the TBM ‘Stella Rose’ being operated by STRABAG. This included 24 hour working, with a squad of up to 20 items of plant and wagons which require extreme flexibility to react to variable advances of the TBM, including limiting costs during maintenance and breakdown periods. We worked to a Materials Management Plan (MMP) in accordance with the Contaminated Land Applications in Real Environments (CL:AIRE) protocol.