Finite Element modeling of geomechanical processes in longwall mining

Abstract

Longwall mining, a method first implemented in the 1920s, has seen significant advancements in recent years with the development of more powerful excavation tools and automated support systems. This research investigates the geomechanical behavior of goafs, the voids created during the longwall mining process, focusing on their potential for repurposing as geothermal energy storage spaces. The study utilizes finite element modeling (FEM) to simulate the displacement, stress distribution of both the goaf and the surrounding intact rock. On that base porosity and permeability evolutions in the goaf are predicted. The modeling approach incorporates elastic and elasto-plastic material properties, with a particular emphasis on plastic compressibility, using the LAGAmine software. The modeling of reference case provides some insights on the geomechanical behavior of longwall mining including the goaf and the surrounding rock. Then the research builds on a real-world case from the Belgian Mining Basin, focusing on understanding the hydraulic properties of rock environments within and near the exploited areas. Four key parameters (the plastic compressibility factor (β), the lateral boundary conditions, the depth of the goaf, the bulking factor b) are analyzed for their sensitivity in affecting the representation of reality and the results of the simulations. The findings indicate that the geomechanical characteristics of the goaf, such as its porosity and permeability, play a crucial role in determining its suitability for geothermal energy storage applications. This study offers valuable insights into the behavior of goafs, showing that with proper modeling, previously mined-out areas could be transformed into valuable assets for sustainable energy storage. The results of this research advance the understanding of how geomechanical processes impact the stability and usability of goafs and highlight their potential for integration into renewable energy systems