Beveiliging van het maaiveld van verlaten mijnschachten in Zuid-Limburg

Abstract

In the South Limburg coal mining district, abandoned pit shafts have to be filled up - at least in the overburden section - in view of the loose nature of the overburden, and the presence of dangerous gasses in the underground workings. In other coal basins with comparable conditions, shafts have been filled down to the bottom with clastic material, generally with special provisions near the shaft insets. In several cases this method resulted in severe subsidence of the filling material and release of firedamp at the surface. In view of this, the following methods have been applied in South Limburg, also taking into account the urbanization of the area. Method I: The supported plug In nine shafts, a concrete closing plug has been placed in the shaft, at the level of the highest loading station. The plug is supported by the floor of the station. The shaft section above the plug is filled up with clastic material. The shaft mouth is capped with concrete. This method was used where the overburden is thick (average: 210m), the shaft opening large (average: 23 sq.m), and the shaft wall smooth. Method II: The shear prop a. In five cases the shaft has been filled up with concrete from the highest loading station to the surface. This method has been followed in the case of a thin overburden (average 43 m), with a short distance from the highest level to the overburden (average: 7 m) and a small shaft opening (average: 11 sq.m). b. In four shafts a shear plug has been placed above the highest level. The section above the plug is filled with clastic material. The required length of the plug depends on the distance to the surface, the size of the shaft opening and the roughness and nature of the shaft wall' The shaft mouth is capped with concrete. The average length of the filled section is 104 m, the average shaft opening is 10 sq.m and the walls have a rough and irregularly shaped surface. c. In three shafts, which have been filled over a considerable length owing to the prevalence of special conditions, a filling of concrete and clastic material, used alternately, has been applied. The concrete sections (shear plugs) are either over or opposite the shaft insets. The topmost shear plug completely separates the surface from the highest level. The shaft mouth is capped with concrete. The fillings with one exception, have shown only slight subsidence. Costs are only 20-50 percent of the amount for filling up the whole shaft and providing barriers at the level of the shaft insets.