Detection of Hazardous Near-Surface Cavities in Karstic Regions

Abstract

Assessment of the risk arising from near surface natural hazard is a crucial step in overcoming foundation problems commonly encountered in engineering projects. It helps clients and other related parties to apply suitable procedures for ground treatment, mitigate potential natural hazards, and minimize human and economic losses. Karstic terrains in KSA is a major challenge for engineering constructions due to extensive occurrence of cavities and/or sinkholes that cause ground subsidence and building collapse. Cavities are air/sediment filled underground voids, commonly developed in limestone rocks by the infiltration of rainwater into the ground, opening up, over a long period of time, holes and tunnels. Mitigation of natural hazards can best be achieved through careful geotechnical studies. Traditionally, engineers use destructive probing techniques for the detection of cavities across regular grids or random distances. Such probing is insufficient on its own to provide confidence that cavities will not be encountered; particularly when the project site is sizable. Frequency of probing and depth of investigation may become prohibitively expensive. Besides, probing is intrusive, non-continuous, slow, expensive, and cannot provide a complete lateral picture of the subsurface geology. Geophysical investigation methods are best suited in site risk assessment (i.e. cavity detection) due to their capability to delineated near-surface cavities and overcome the limitations of traditional probing techniques. This of course helps engineers to develop the appropriate plans of hazard mitigation and implement accordingly the suitable engineering design. Several studies reported in literatures have utilized geophysical techniques for site characterization of karstic regions (Dunscomb and Rehwoldt, 1999; Kaufmann and Quinif, 2001; Roth and Nyquist, 2003). Although these techniques (e.g. resistivity, Seismic…etc) are disparate in their application and efficiency, they have proven good satisfactory results in different geological situations.