Interaction of old near surface coal mining and a road construction project
The new connecting road K 24n is to be built in the most northern expanses of the coal mining area in the Ruhr region. The road axis runs through an area partly affected by old surface near mining operations. The coal is located in two seams, both dipping north with an angle of approx. 11°. These seams have been mined by three potential drifts, which have been identified by a geophysical field study.
The investigate of possible safety measures was one focus of Itasca’s work. Based on a reference case and different variations regarding the material parameters, the effect of backfill in the street course was investigated for areas influenced by mining. A concrete with low strength properties is used as backfill. Figure 1 shows the full model, including the vicinity of the road construction (green), the coal seams and mining drifts (dark grey) as well as the areas that are backfilled with concrete (blue).
The investigation of the variation and reduction of rock and soil material properties as well as the coal tailings resulted in moderate displacements.
The subsequent investigation of the described safety measure resulted in decreased settlements of the reinforced area. This effect can be seen in Figure 2, where reduced displacements can be observed in the road course. Itasca suggested the client to investigate the condition of the coal seams and the old mining drifts and if they prove to be in unstable condition to increase the stability of the underground.