Advancing Underground Space Geomechanics for Post-Mining Land Use at Legacy Tin Mine Sites in North Central Nigeria

Legacy tin mine workings on the Jos Plateau in Plateau State, North Central Nigeria, have created a complex underground space that constrains surface land use and poses subsidence risk to overlying communities. This dissertation advances knowledge of underground space geomechanics relevant to safe post-mining land use planning at legacy tin mine sites in North Central Nigeria. A comprehensive characterisation programme investigated the geometry, support condition, and residual stability of accessible remnant underground workings across four decommissioned mine areas through underground mapping, LiDAR scanning, and rock quality assessment. In-situ stress measurement was performed at three accessible locations. Finite element modelling using RS3 software was used to assess long-term stability of unsupported underground spaces under progressive deterioration of rock support conditions. Subsidence potential was evaluated using empirical profile functions derived from monitored subsidence data at analogous legacy mines in West Africa and Europe. Results identify 23 specific zones of residual underground excavation within the study areas where time-dependent collapse risk poses an unacceptable constraint on planned surface land use, including housing and infrastructure. A probabilistic risk-zoning approach to post-mining land use planning is developed and validated through expert panel review. The dissertation delivers the first geomechanically grounded underground space hazard classification system applicable to the Jos Plateau mining legacy and proposes its adoption in Plateau State land use planning legislation. Keywords: underground space, geomechanics, post-mining land use, Jos Plateau, subsidence risk.