Gravity investigations of recent sinkholes and karst pits of Dahal Al-Hamam, State of Qatar

Gravity prospecting is a very useful geophysical technique for the investigation of karst subsurface features, in urban areas, which are a common natural hazard in several parts of the world. Gravity data were used to determine the subsurface conditions in central Qatar to map zones vulnerable to sinkhole formation in the vicinity of Dahel Al-Hamam area in the State of Qatar. Gravity modeling was a useful technique to map the spatial extension of the karts topography associated with these sinkholes. Clusters of closely spaced contours of low gravity values observed in the northeastern part of the studied area are indicative of relatively very low negative anomaly which points to missing mass due to karst processes. This was interpreted as either as an air-filled or water-filled sinkhole. The obtained video images of the subsurface features of the studied area confirmed that the existing subsurface caves are water filled. The extension of the sinkhole and associated openings are connected to the Arabian Gulf. To prevent the growth of associated underground cavities, the bibliographical research indicated that filling up the uppermost voids with stable grout mix is one of the appropriate treatment options to help reduce the macro-permeability of the rock and to prohibit the migration of the favorable conditions of cavity formation. The findings have both local and general applications. Locally, the findings delineate the subsurface extension of the karst topography, and it is generally demonstrated that non-invasive surveying methods constitute a useful tool to enhance knowledge on sinkhole phenomenon.