Mechanisms of Soil Collapse and Induced Sinkholes in Evaporite-Bearing Formations of the Benue Trough: A Geomechanical Investigation

Subsurface dissolution of evaporite minerals within Cretaceous formations of the Benue Trough has been invoked as an explanation for localised ground collapse events and sinkhole formation reported from communities in Benue and Taraba states, but the hydrogeological and geomechanical mechanisms driving dissolution and cavity collapse remain poorly characterised in this context. This study investigates the mechanisms of soil collapse and induced sinkholes in evaporite-bearing formations of the Benue Trough through integrated hydrogeological monitoring, geophysical investigation, laboratory dissolution experiments, and geomechanical numerical modelling. A network of piezometers and water quality monitoring stations was established to characterise the hydrogeological conditions facilitating evaporite dissolution, with sulphate concentrations and electrical conductivity used as proxies for dissolution activity. Electrical resistivity tomography and ground-penetrating radar surveys were conducted over identified collapse zones to image subsurface cavity geometry. Laboratory dissolution rate experiments on gypsum and anhydrite samples from formation core samples were conducted under controlled temperature and flow conditions to derive dissolution kinetics. Discrete element method numerical modelling was applied to simulate roof collapse above dissolving cavities as a function of cavity dimensions, roof rock properties, and overburden stresses. The study develops an original hazard classification scheme for evaporite dissolution-related subsidence applicable to infrastructure siting decisions in the Benue Trough region. Keywords: evaporite dissolution, sinkholes, geomechanics, Benue Trough, subsidence hazard.