Numerical modelling of shallow abandoned mine working subsidence affecting transport infrastructure

This work presents details of a shallow mining subsidence event that occurred in the summer of 2001 causing the formation of crown-holes at the surface which affected the East Coast Main Railway line in the UK. This subsidence event caused significant disruption and the remediation effort required the construction of a 1.8km long diversion built on a piled, reinforced concrete raft. Details of the ground investigation are summarised along with a large parametric numerical modelling study undertaken in FLAC 3D into the potential causes of the instability, including the role of variations of the level of the groundwater table, the influence of the structure of the rock mass and also the potential geometry of the abandoned workings. Ultimately the modelling allowed constraints to be placed on the likely excavation width of the workings at the site along with bedding spacing and strength of the overlying rock mass. The modelling also suggests that the increase in the ground water table may also have been a factor in the occurrence of instability on the site. ► We present a case study of a subsidence event effecting transport infrastructure. ► The subsidence is a result of the collapse of shallow abandoned colliery workings. ► Numerical modelling is undertaken to understand the causes of the event. ► This allows constraints to be placed on rock mass strength and stiffness properties. ► Fluctuations in groundwater table appear to be significant in triggering subsidence.