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Over coal shafts, Phoenix 10, Walsall, UK

John F Hunt Regeneration Ltd (JFHR) has been awarded an enabling works package for the Phoenix 10 site in Walsall. Prior to bulk excavation and re-engineering of a landfill that exists across the entire site, drilling and grouting of former mine shafts and coal mine workings is required. The drill and grout works are to be designed and undertaken by sub-contractor Forkers Ltd.

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Analyses were conducted using the methods for designing geosynthetic reinforcement over areas prone to subsidence given in BS 8006-1. The BS 8006-1 design approach assumes a constant volume of soil in the zone of depression. The zone of depression is assumed to be an inverted, truncated wedge (longitudinal subsidence area) or cone (axisymmetric subsidence area). The dimensions of the zone of depression can be quantified in terms of the vertical depth of the surface depression, dS, and the deformation diameter at the surface of the embankment, DS. In BS 8006-1 (2010) the angle of draw, is equal to the angle of friction of the fill above the reinforcement. High strength geogrids (between 400 - 1,500 kN/m) were selected for this project to span shafts with maximum diameter of 2.5m. Geogrids partial factors have been incorporated into the analyses in accordance with BS 8006-1.

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Engineered Fill is to be formed from excavation and processing of the existing landfill materials. The Client’s Earthworks Specification requires that earthworks materials be be placed in general accordance with the Specification for Highway Works (SHW) Series 600. An End Product has been specified such that materials placed and compacted around and above the shafts will be at 95% Maximum Dry Density and with maximum 5% air voids. The project is due to start in September 2022 - more pictures to follow when available.

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