Articles | Volume 16, issue 9
Research article
14 Sep 2016
Research article |  | 14 Sep 2016

Surface movement above an underground coal longwall mine after closure

André Vervoort

Abstract. The surface movement in an area of about 22 km2 above the underground coal mine of Houthalen was analyzed based on Interferometry with Synthetic Aperture Radar (InSAR) measurements. After its closure in 1992, a residual subsidence was observed over a period of several years, followed by an uplift of the surface above and around the past longwall panels, whereby the rate of movement was, in absolute terms, of the same order for the two types of movements. The processes behind these movements are different. The process of subsidence is caused by the caving of the roof above the mined-out area and is mainly a mechanical stress-deformation process, including time-dependent aspects. However, the process of uplift is most probably caused by the swelling of the clay minerals in the argillaceous rocks in the coal strata after the flooding of the underground workings. Hence, the areas in which there is the greatest risk of damage to the surface infrastructure are not the same for the hazards linked to subsidence and uplift. For example, the zone in which the maximum uplift occurs clearly is at a different location from that of the zone with the maximum residual subsidence. There is no clear sign that the amount of mining underneath affects the residual subsidence, and there is no indication that the process of uplift is linked directly to the mining characteristics. It is more likely that uplift as the result of flooding is initiated at, or close to, the vertical shafts.

Short summary
Underground coal mining induces surface movement with damage to infrastructure. The best known phenomenon is downward movement or subsidence during the life of the mine. However, it has been observed that after the closure of the mine there is first a period of still residual subsidence, followed by upwards movement or uplift. This uplift is the direct result of the flooding of the underground workings. By conducting this research, the long-term impact of mining is better quantified.
Final-revised paper