The detection of abandoned mine shafts in the Netherlands

In the Old Coal Mine District of East Limburg, in the south of the Netherla nds, 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 sh afts urgently need to be secured for reasons related to a recent rise in de ep ground water levels, but only approximate shaft coordinates are known. T his 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 indica tes that the chances of finding clues for abandoned mine shafts are reasona ble, and that digital techniques facilitate identification and exact determ ination of shaft coordinates, In a densely populated survey environment, su ch as the area in which the abandoned shafts are located, georadar is a sui table shallow geophysical method for mine shaft detection. In these circums tances, shielded antennae give a clearer subsurface image than unshielded a ntennae. Signal penetration in the loess-rich deposits commonly found in th e 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 s haft center.