Our earthworks at Gateway 36 in Barnsley, formerly Rockingham Colliery, continue to make great progress as we undertake the second phase of the surcharging and ground treatment strategy. This strategy was designed by the RSK Group, an engineering and environmental consultancy working with the project client, the Harworth Group.

Previously, in the first phase of surcharging, we excavated a borrow pit and used the surplus landscaping material, to form the first surcharge mound. This first mound was 170,000m3 (with an estimated 90,000m3 coming from the borrow pit) and was placed on units 6 and 7. This surcharge stayed in place from December 2022 through till May 2023, when the Geotechnical Engineer had fully assessed that the settlement had ceased. Beneath the footprint and load of the surcharge, the settlement was between 200-400mm.

The second phase of the strategy officially commenced in May. The first works that began involved backfilling and reengineering the borrow pit (the other half of the development plateau). The engineered fill is required to be benched back in, and compacted to a high specification to ensure that the development plateau is structurally sound and viable for use. Following the completion of the borrow pit reinstatement, we will then proceed with installing the monitoring infrastructure, followed by moving the remaining surcharge material onto the borrow pit area – the other half of the development plateau, which is also to be surcharged.

There will be insufficient material to form the 2nd surcharge mound from just the surplus material alone, meaning we will need to borrow pit again from the area previously successfully surcharged. Overall, the surcharge/load required in this phase is 160,000m3, with approximately 80,000m3 coming from the new borrow pit. Following the formation of the second surcharge, it’ll be left to induce settlement, though the length of this period cannot be determined. Expectations dictate this period being at minimum three months, with the more likely estimate ranging to six.

Another important point of note is that, for the second phase of works, we have been instructed to undertake the topsoiling and initial landscaping works to 75% of the batters of the various development plateaus. This will see us place in the region of 20,000m3 of topsoil.

Looking ahead to the future of the scheme, the third phase will begin next year. Following the completion of the 2nd settlement period, we will reengineer the material back into the borrow pit, and leave the surplus material in place in a sealed stockpile. As of right now the surplus material’s end use is not defined, but is likely to go into landscaping bunds around the development.

For an in-depth case study of the works taking, visit the case study on our website here.