Mapping possible karst voids under building foundations in the Gulf using seismic surface waves with the Square Array Void Mapping (SAVM) technique

Near-surface geophysical methods provide a means to acquire non-intrusive high-resolution images of the shallow subsurface environment for engineering, hydrography and structural targets. Multichannel Analysis of Surface Waves (MASW) is a widely used method to detect near-surface voids, cavities, and stratigraphic information for engineering projects over open and accessible areas. Often sites can be unsuitable for such surveys due to construction or accessibility. Square Array Void Mapping (SAVM) technique is a method that is used where volumes of ground need to be surveyed and/or where the target area of the survey is inaccessible due to construction or excavation. The SAVM technique uses arrays around the location of the survey area to undershoot the ground between the source and receiver arrays. It is used to model the variation in the ground across the 3D volume surounded by the array. Like MASAW, different frequency bands generate different depth sensitivities for the surface waves. Analysis on each frequency packet alows the seperation of the modeled data into depth bands. Contrasts in the data from the site norms can be used to identify anomolus areas and highlight potential issues within the 3D block. On a construction site in the Gulf region, the SAVM survey was conducted in a square geometry for the presence of voids and cavities within limestone/calcarenite bedrock. The results of the SAVM survey were delivered to the client for further investigation and remedial measures.