Abstract. In the region of Maastricht, both in the Netherlands and
in Belgium, about 400 room and pillar mines have been excavated in weak
Upper-Cretaceous limestones. Pillar instability has resulted in a number of
large-scale collapses and serious surface subsidence with faulting and
sinkhole formation. The Heidegroeve used to be a very stable mine for more
than 50 years, until pillars started to fracture and spall unexpectedly in
the summer of 1987. The collapse of the abandoned mine occurred in June
1988, and was initially detected when faults and sinkholes had formed at the
surface. Originally it was postulated that just creep deformation inside this mine
was the main cause. However, a stability analysis revealed that all pillars
inside the collapse area showed sufficient safety factors and should still
be intact, while the weakest part, with several pillars of insufficient
strength, had been fractured but is still standing. In the vicinity of the
collapse area mines have been excavated at a lower level. Therefore it was
postulated that the collapse of the Heidegroeve was related to an unknown
and inaccessible continuation of these mine workings underneath. Indeed,
recent, rather adventurous fieldwork revealed a downward collapse-induced
fault giving access to open galleries and collapse structures about 3.5 m
below the Heidegroeve. Inside the collapse area of the Heidegroeve itself,
accessible through openings between the debris fragments, severe tilting of
gallery floors was observed, which was probably brought about by punching of
pillars of the lower mine. This case study with an unusual result shows that great care must always be
taken in the analysis of the stability of mines and the assessment of the
risk of surface subsidence.
Underground coal mine workings as potential places for Compressed Air Energy Storage
