Mitigation of ancient coal mining hazards to overhead line equipment structures

Subsidence and collapse of structures supporting overhead line equipment (OLE) due to legacy coal mining can be catastrophic during both the construction and operational phases, causing damage to construction plant, injuries and fatalities to the construction and maintenance workforce, failure of the track and disruption to the operational railway. When applied to linear railway schemes spanning considerable distances, industry guidelines for appraising and mitigating these mining hazards are overly conservative with a disproportionate cost. On phase 4 of the North West Electrification Project between Manchester Victoria and Euxton Junction, an innovative risk-based method was devised and implemented to identify and mitigate mining hazards to OLE structures. Formulation of these value-engineering solutions prevented programme drift and led to significant cost savings. Details of this methodology, including a detailed desk study, computational geomechanics, a well-targeted ground investigation, void remediation and real-time foundation monitoring, are discussed in this paper.