Mapping hazardous cavities over collapsed coal mines: Case study experiences using microgravity method

ABSTRACT Examples of the application of microgravity mehtod for the detection of potentially hazardous (empty) underground cavities caused by the collapse of coal mines are presented. Within these areas some alteration by previous remediation activity had occurred. This was not documented earlier and, therefore, such alteration was often unknown prior to the current investigations. We show a successful application of microgravity, leading to the detection of an empty cavity, in close proximity to where concrete injection was earlier performed. This was subsequently verified thorugh measurements in a borehole. In contrast, two other examples delivered results where the microgravity data, along with signals from other geophysical methods, led to the interpretation that subsidence resulting in the formation of sinkholes had been in‐filled, and in these situations the detection of more recent cavities was considered to be unreliable. These results point to the conclusion that microgravity interpretation of cavities is an effective approach, but the success of this approach may be compromised at sites where remediation activity has already occurred; in such situations the approach should be supplemented by other geophysical methods.