Geophysical performance of subsurface characterization for site suitability in construction purpose

Abstract

Geophysical investigations are indirect methods of characterization of subsurface materials. Detailed information about the underlying subsurface is essential in preventing foundation failure and comprehending ground conditions. Seismic refraction is the most commonly used method for site characterization. Most researchers use this method with borehole data to investigate the subsurface. However, it is not adequate to rely on one method. To achieve an optimum result, it is best to apply different techniques and, as far as possible, integrate their results. The research aims to identify the shallow subsurface using geophysical techniques, correlate the results with the borehole data, estimate the rippability of rocks based on seismic velocity, and recommend a suitable foundation depth. 2D resistivity and seismic refraction methods were employed. Results show two resistivity zones. The lower resistivity zone (1–700 Ωm) comprises the loose and weathered zone, and the higher resistivity zone (700–4000 Ωm) indicates a more competent and compacted zone. The seismic interpretation reveals three subsurface layers. The first layer has an average velocity of 300–1600 m/s, indicating loose and unconsolidated soil with low N-values. The second layer (1600–2900 m/s) is interpreted as a stiffer and more competent layer. The third layer (2900–3800 m/s) is the most competent layer characterised by its high stiffness, and high N-values. The depth of rippable materials changes across sections, ranging from subsurface to a depth of 5 m. A marginal zone between rippable and non-rippable materials exists at a depth of 5–13 m. Non-rippable materials are below the depth of 13 m. The combined approaches' findings indicate that the area has the sufficient bearing capacity and is acceptable for construction; this will be considered when designing and constructing structures.