Urban Geophysical Investigations to Map Karstic Conditions for Planned Tunnel Construction, Doha, Qatar

The city of Doha is undergoing rapid expansion with extensive infrastructure development in progress. The ground conditions in Doha however are karstic, which is a major risk during construction. Cavities and sinkholes are known to exist in the Doha area in various sizes up to several hundreds of cubic meters. As part of the transport infrastructure development a series of cut and cover tunnels are planned in central Doha. Dependence on geotechnical drillings along the tunnel alignment is insufficient to fully ascertain the risks of potential cavities. As part of the geotechnical investigations geophysical surveys were conducted to identify potential cavities along the planned tunnel segments. This work presents the results of geophysical surveys carried out which consisted of electromagnetic, Multichannel Analysis of Surface Waves (MASW) and Electrical Resistivity Tomography (ERT). Resistivity and MASW surveys with good quality are able to be obtained within the urban conditions of the survey site. The Weathered Limestone is able to be mapped with the MASW method. There are occurrences of low velocity zones indicating increased likelihood of cavities at identified locations. Overall the use of these non-invasive and cost efficient methods allowed reducing the number of boreholes to be placed.