Geophysical and intrusive site investigations to detect an abandoned coal-mine access shaft, Apedale, Staffordshire, UK

Derelict coal mine workings at Apedale in Staffordshire, United Kingdom were the focus for a multi-disciplinary geophysical and intrusive site investigation. Objectives were to: 1) locate the surface entrance to a coal mine access shaft, 2) determine the inclined shaft's changing depth below present ground level, 3) determine if it was open, partly or fully filled, 4) locate it beneath a known shaft if (1) was unsuccessful and finally 5) compare geophysical mineshaft detection techniques in difficult ground conditions. After initial site reconnaissance, desktop study and modelling, field work collected surface micro-gravity and electrical resistivity imaging (ERI) 2D profiles to locate the shaft and entrance area. The made-ground nature of the site made identification of clear geophysical anomalies challenging. Subsequent intrusive investigations to locate the entrance were unsuccessful. A second phase of fieldwork down a known mineshaft imaged three geophysical anomalies beneath this shaft floor; after comparison with modelled data, subsequent intrusive investigations of the ERI anomaly successfully located the target shaft. Collapsed material was progressively cleared to the surface and a new shaft entrance stabilized. Surface micro-gravity 2D profiles surprisingly did not produce clear target anomalies, likely to be due to the target depth below ground level and the variety of above-ground, relict mine structures present. Surface ERI 2D profiles were less affected by above-ground structures but investigated anomalies were found to be heterogeneous ground materials. Comparisons of 2D micro-gravity, ERI and ground-penetrating radar profiles collected within a mineshaft showed ERI data were optimal. 2D micro-gravity and ERI modelling were shown to aid geophysical interpretations.