In the former lignite mine "Robertshall" near Hamburg damage to the surface was caused by the collapse of underground cavities originating from old mine workings of a lignite mine which had been in operation between 1920 and 1922. During the investigation of the subsurface by drilling it was noticed that the existing mine plans are incomplete.
If mine plans are missing or incomplete, the risk to protected assets at the surface due to mining damage can often only be reliably assessed by means of indirect methods such as geophysics in reasonable combination with drilling. Within the scope of this work the extend of room-and-pillar caving at the “Robertshall” deep lignite mine was determined by geophysical methods. Subsequent backfilling and securing of the old mine workings are the goals of this exploration.
The simultaneous application of several methods on the selected test profile is not only intended to increase the reliability of the results, but also to gain experience as to which methods are best suited for routine detection under the given geological and mining conditions. The geophysical measurements are supplemented by an evaluation of historical data.
The results of geophysics have led to the prompt and reliable discovery of many drifts that were not included in the mine plan. Compared to the conventional approach of exploration by drilling, the application of seismic measurements saves time and costs.
The securing measures could be carried out by the responsible parties and the desired securing success has been achieved so that no further movements of the ground surface are to be expected.