Long-Term Stability and Sealing of the König-Ludwig Shaft in the Stockheim Coal Mining District, Bavaria

This study addresses the instability issues of abandoned mining shafts with an emphasis on the König-Ludwig shaft in North Bavaria. A long-term sealing solution is required since subsidence problems have continued despite prior attempts to stabilize and seal the site. Using both analytical and numerical techniques, the study investigates an optimal shaft sealing strategy. The objective is to place concrete plugs and fill the shaft with concrete grouts as a long-term sealing solution. These two types of considered concrete plugs encompass single parallel and single frustoconical and aim to install them in the hard rock surrounding part of the shaft. To obtain a complete understanding of the stability and stress distribution within the König-Ludwig shaft under varied geological and loading circumstances, a three-dimensional numerical simulation using FLAC3D has been conducted. The maximum plug length of 3 meters guarantees the necessary safety factor, ensuring structural stability under various loading situations, according to the analytical calculation for plug dimensioning. Nonetheless, the results show that the stability of the shaft is met after sealing, and both single parallel and single frustoconical plugs showed minimal displacement. The findings also demonstrate that because of directed shear stresses, inclined strata exhibit larger localized stress concentrations and need more solution steps. In order to avoid instability throughout the shaft, a formula is also developed to estimate permitted loading limits to prevent exceeding the allowable deflection limits.