Geotechnical studies for evaluation and limitations of environmental and engineering hazards that affect the economic infrastructure in Abha, Saudi Arabia

Abha is the capital of Asir province in Saudi Arabia. It is situated 2200 meters (7200 ft) above the sea level in the fertile mountains of the south-western Saudi Arabia. One of the most important structures of this region is Abha dam that acts as a barrier that impounds water or underground streams thereby retaining the ground water of the region. With the passage of time, various environmental factors such as ground movement, wind and changes in temperature may have significant effect on these various structure factors and may lead to invisible cracks and other structural defects. Because the dams and tunnels are prone to sudden collapse, there is potential great risk to lives of the people and significant economic loss in this area. The use of the ground penetrating radar (GPR) and electric resistivity techniques is a non-invasive scan and could assess the conditions of various built structures as well as the earth beneath or surrounding it. So the GPR system with appropriate types of antennas (1.5 GH, 1 GH, 400 MH and 100 MH) and electrical resistivity in one dimension (VES) and two dimensions (electrical profiling and imaging) is used in this work. This work aims to investigate the dam structure, developing cracks or areas of increased moisture. Also to study the surrounding areas to detect seepage from pond that may affect nearby buildings and the dam itself.
It reveals that, the depth of water bearing layer ranges from 2 m to 10 m, where the three geoelectric layers are present. The first layer has resistivity values ranging from 44 Ω m–1200 Ω m with thickness ranging from 3 m to 18 m that is interpreted as the wadi deposits. The second layer having resistivity values from 11 Ω m to 137 Ω m is interpreted as the water saturated in the fractured basements. The third layer of resistivity values ranging from 2200 Ω m to 90,000 Ω m is interpreted as dry, massive basements. The GPR results provided internal images of the slab, showing its morphology, areas of possible damage and changes to the structure, and the situation of the steel reinforcements. It showed the presence of different shapes of fractures and voids with the growing of moisture zones.