Abstract

The stability analysis of underground mine systems with complex 3D geometry is still a challenging task, especially when abandoned mines are planned for new uses with public access, that imply more restrictive safety requirements. This inherently multi-scale problem requires both the evaluation of the global mine stability and the assessment of local deformation and failure mechanisms of individual pillars or roof sectors in a robust 3D modeling framework. We integrated 3D remote survey techniques and FEM 3D modeling to perform a comprehensive stability analysis of an abandoned fluorite mine system in the central Southern Alps (Italy), including ten levels excavated in bedded limestones. We reconstructed the 3D geometry of three levels undergoing a reuse plan, combining a dynamic LiDAR system and close-range photogrammetry. We used point clouds in a workflow to generate solids, excavate the 3D analysis domain and generate a FEM 3D mesh for numerical modeling. We performed a series of continuum-based FEM 3D simulations of mine excavation and rock mass strength degradation. Our results allowed assessing the global stability of the abandoned mine and identifying critically stressed roof sectors and pillars to prioritize the local-scale analysis, remediation and monitoring of critical spots.

Introduction

Abandoned mines are increasingly recognized as valuable assets that can be reused in different ways, including civil uses (e.g. commercial, recreational or educational) or storage of different types of goods (e.g. food), waste or resources as oil and water [1]. Nevertheless, abandoned mines can undergo progressive decrease of stability conditions due to chemical weathering, progressive rock damage accumulation and uncontrolled variations of groundwater regime, constrained by geological and environmental conditions. These processes can result in subsidence, flooding or catastrophic failure threatening life, properties, and the environment [2,3]. Moreover, civil reuse of former mining voids has increased safety requirements with respect to active mining environments and must be supported by suitable design and monitoring measures. Dealing with abandoned mines requires a robust assessment of the stability conditions of underground structures, considering the site-specific geological conditions and mining layouts, yet it remains a difficult task.

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