Relationship between joint movement and mining subsidence

The hazards associated with the possible collapse of old mine workings underlying an active landfill site in north-east England have been identified as a significant concern to both the regulatory authorities and to the landfill operator. A quantitative assessment of the hazards and their perceived risks to the integrity of the composite lining system in place beneath the landfill has been undertaken using a combination of field observation, established mine subsidence prediction tools and numerical modelling techniques. Field observations have identified the presence of extensive fissuring within the limestone underlying the site, however, it is difficult to assess the extent to which mining has contributed to the development of these features. In light of this, an influence function technique has been used to attempt to predict the degree of fracturing that could have been experienced at the surface due solely to mining, with the intention of illustrating whether the scale of movements on pre-existing joints could be attributed to mining subsidence. The results of this analysis have subsequently been used within a finite-difference numerical model to assess the effect that a fracture of the scale predicted would have on the composite lining system.