ABSTRACT
Resistivity sounding, a geophysical mean for determining electrical earth resistivity with successively increasing depth from the ground surface, becomes more and more an efficient help for civil and soil engineers investigating land sites dedicated for civil works. This paper will present cases of resistivity surveys made in Syria (in the very vicinity to Damascus) on 4 different ground pieces, close to eachother and dedicated for building of multi-etage houses. More than 500 soundings (VES-points) were measured along equidistant (every 4 m) profiles crossing the investigated sites, the sounding stations on every profile were only of 2 m distance of eachother. The electrode array used was a modified Schlumberger with the current electrode moving along OA = 1; 1,5; 2; 3; 4; 5; 7; 10; 10; 15 m, while the potential electrodes, very close to eachother, were fixed to MN = 0,5 m. The so gained resistivities were then evaluated and interpreted for every ground site. They were plotted as horizontal cross sections with the pseudo-depth (isoresistivity maps) and as vertical pseudo-cross sections along the different measuring profiles as well as a 3D-image, reflecting the structural inhomogenities in the rocks under the site, for the first 10 to 15m from the surface. The four investigated ground pieces at Dummar (urban city of Damascus), have revealed different types of inhomogenities, due to the different rock types, cutting the surface area of every site. A cavity, already cut through preparatory excavation work could be well outlined (contoured) in its extention by the resistivity image. According to the geophysical survey, soil engineer and construction engineer could locate the proper places for a representative, efficient and economical sampling (open bits or boreholes) of the earth under every ground piece, choosing the right solutions to ensure safty and stability of the planned multi-etage houses. The special array used has proved to be most valable for such engineering geological studies, because it is: • more flexible to do measurements on small ground pieces and, • more sensitive for vertical or steep dipping rock inhomogenities (faults, fissures, cavities...) and, • time safing due to moving of almost I electrode during sounding.
