Stability and Subsidence Assessment over Shallow Abandoned Room and Pillar Limestone Mines

Abstract

In the region of Maastricht, both in The Netherlands and in Belgium, many areas are underlain by abandoned room and pillar mines, which have been excavated in weak limestone to produce building stone. Several of these mines are kept open now to serve as an important tourist attraction. However, there have been both local and large-scale collapses up to the present, resulting in extensive surface subsidence, faulting, and sinkhole formation. For many mines the stability needs continuous attention. Depending on rock overburden thickness, mine span and density of joints, different collapse and subsidence mechanisms can apply. This contribution describes these mechanisms and then concentrates on how to assess the potential of a large-scale pillar collapse of a room and pillar mine. This quantitative assessment is based on short- and long-term laboratory tests on model pillars, numerical experiments and numerous field observations, taken during more than 20 years. Only taking the stability of individual pillars into account cannot assess the collapse potential of a mine. Particularly large-scale pillar stability, which considers the load carrying capacity of all pillars together, and general mine stability, which concerns the arching capacity of the overburden, are important. In the recent past, the method was applied successfully to several mines, in order to investigate the necessity of underground support measures to protect existing infrastructure and planned infrastructural projects. It is expected that at least a major part of the method applies to shallow room and pillar mines in other regions and rock types.