Abstract
This study addresses the complex issue of rock mass stability in mining operations, with a particular focus on lignite deposits in challenging geological conditions. The primary objective was to develop a detailed and integrated geomechanical mathematical model capable of assessing and managing associated instability risks. The study began with an in-depth characterization of the geomechanical properties of the specific rock types found in these environments—marls, clays, aquifer sands, and lignite. This analysis highlighted the lithological variability and rheological behaviour of these materials, including creep phenomena. A crucial component involved analysing the influence of hydrogeological conditions, identifying the complex role of aquifer and aquiclude horizons in groundwater dynamics and infiltration risk. For risk assessment, an integrated cause-and-effect analysis was employed, utilizing visual tools and a risk matrix. This approach revealed that hydrogeological and geological factors represent critical risks, exhibiting the highest impact and probability of occurrence. Mining activities were classified as high-risk, while geomechanical and external factors presented moderate and low risks, respectively. Based on this prioritization, a detailed action plan was structured, including measures for monitoring, controlled drainage, reinforcement, and operational optimization. The central objective of this work, the development of the geomechanical mathematical model, was achieved by describing its theoretical foundations. This model incorporates equilibrium and compatibility equations, advanced constitutive models (elastic-plastic Mohr-Coulomb, rheological Bürgers for creep, and linear elastic), and, critically, hydro-mechanical coupling based on Terzaghi’s effective stress principle and Darcy’s law. The complexity of this system of nonlinear, coupled partial differential equations justified the necessity of employing numerical methods for its solution. This study provides a robust analytical basis and a dynamic tool for understanding and managing rock mass stability in challenging geological environments. Its contribution lies in providing an integrated framework that enables the safe and efficient design of mining operations, thereby contributing to risk minimization and the sustainability of lignite deposit exploitation.