The Detection of Abandoned Mine Shafts in the Netherlands

In the Old Coal Mine District of East Limburg, in the south of the Netherlands, a number of abandoned mine shafts exist of which the exact coordinates are uncertain. The area is now densely populated, and the majority of the shafts are located near or underneath roads and/or houses. Some of these shafts urgently need to be secured for reasons related to a recent rise in deep ground water levels, but only approximate shaft coordinates are known. This paper describes preliminary investigations for abandoned mine shafts by means of aerial photographs and georadar. Dutch photo-archives hold aerial photos dating from 1935 onwards. Inspection of various photo series indicates that the chances of finding clues for abandoned mine shafts are reasonable, and that digital techniques facilitate identification and exact determination of shaft coordinates. In a densely populated survey environment, such as the area in which the abandoned shafts are located, georadar is a suitable shallow geophysical method for mine shaft detection. In these circumstances, shielded antennae give a clearer subsurface image than unshielded antennae. Signal penetration in the loess-rich deposits commonly found in the area is limited, but the results of a trial survey over a known abandoned shaft accurately confirm the geometry of a collapse zone surrounding the shaft center.