Original Contribution to Geomechanical Modelling of Caving Propagation in Weak Rock Mass Conditions at Deep Nigerian Iron Ore Mines

Block caving is an increasingly relevant underground mining method for deep, bulk ore bodies such as the deeper extensions of the Itakpe and Agbaja iron ore deposits in Nigeria, yet the geomechanical behaviour of caving propagation in the weak to moderate rock mass conditions characteristic of these deposits is not adequately captured by existing caving models. This dissertation makes an original contribution to geomechanical modelling of caving propagation in weak rock mass conditions applicable to deep Nigerian iron ore deposits. A series of physical analogue scaled model experiments using synthetic materials calibrated to representative weak rock mass properties was conducted to observe caving initiation and propagation mechanisms under various extraction footprint configurations. Results from physical models were used to validate and calibrate a three-dimensional hybrid finite-discrete element numerical model constructed in IRAZU software. A novel geomechanical index, the Weak Mass Caveability Index (WMCI), is developed as an original contribution to characterise caving potential in rock masses below Rock Mass Rating 40. The WMCI integrates intact rock strength, joint frequency, joint condition, and in-situ stress ratio into a single predictive parameter. Validation against published cave performance data from four comparable international operations confirms the WMCI's predictive reliability for cave initiation timing and hydraulic radius requirements. Application to Itakpe deposit geomechanical data predicts viable caving at a hydraulic radius of 28 metres. The dissertation provides design guidance for future cave mine planning at Nigerian deep ore bodies. Keywords: block caving, geomechanical modelling, weak rock, iron ore, Nigeria.