Abstract
In the present study, the existence of cavities, voids, and fractures was verified at the site of the El-Elb Dam, which is located to the northwest of Riyadh City acrossWadi Hanifa, using 2D electrical resistivity tomography (ERT) and ground-penetrating radar (GPR) techniques. For this purpose, four ERT profiles were measured on the downstreamside of the El-Elb Dam using the Syscal Pro Switch-72 resistivity meter. In addition, a GPR survey using a 400-MHz antenna and a SIR-3000 instrument was conducted along five profiles above the stilling basins on the downstream side of the dam and one radar profile was measured outside the stilling basins area across the course of the wadi. The resultant geophysical data were interpreted with the aid of information from a field-based structural and stratigraphic evaluation of the outcropped bedrock on the banks of the wadi course. The analysis of the inverted ERT and filtered radar sections revealed several resistivity and electromagnetic reflection anomalies that are identified laterally and vertically across the measured sections. These anomalies indicate the presence of fractures and karst features affected the limestone bedrock in the dam site. These near-surface karstified and fractured strata represent a critical hazard to the structural safety of the dam.