Shear wave velocity profiling of Riyadh City, Saudi Arabia, utilizing the multi-channel analysis of surface waves method

Geotechnical site characterization is very important for construction purposes. This study has been conducted in Diriyah area northwest of Riyadh City, Saudi Arabia, using the Multichannel Analysis of Surface Waves (MASW) method for site characterization through shear wave velocity profiling to 30 m depth. Nineteen MASW lines were carried out in various directions and lengths through the area. The entire process was meticulously parameterized to extract shear wave velocity for subsurface characteristics. MASW results revealed four distinct velocity zones based on National Earthquake Hazard Reduction Program. Fill material was approximately half a meter thick and was classified as very dense soil. The second layer exhibited velocities ranging from 800 to 1,500 m/s, indicating weathered and highly fractured limestone. The third layer showed velocities varying from 1,500 to 1,800 m/s, representing slightly weathered limestone. The fourth layer displayed high velocities ranging from 1,800 to 3,600 m/s, indicating hard and compact limestone rocks. Geotechnical boreholes were drilled down to depths of 10-35 m. These boreholes exposed the geological model that consisted of fill material (silty sand with gravel), followed by highly to moderately weathered limestone with vugs and cracks, and finally, massive limestone rock. Analysis of shear wave velocities identified weak zones, particularly fractured and weathered limestone rocks extending to 12 m in depth. Sinkholes of circular, elongated, and/or conical shapes were observed within this depth range. Moreover, some sinkholes were detected at depths greater than 12 m in specific locations (sites 1, 6, 9, 11, and 17). These sinkholes agreed with the previous study. These results highlight the need for targeted ground improvement methods, such as grouting or underpinning, particularly for construction over weaker zones. Accurate site classification and effective risk management are crucial for addressing these geotechnical and seismic challenges.