Geotechnical site investigation using seismic refraction and resistivity techniques

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2D siesmic refraction and electrical resistivity surveys have been conducted at the KNSUT Business School extension site to find out how suitable the subsurface is for building construction purposes. The survey focused on using resistivity and p-wave velocity values obtained from the subsurface at the study area to predict clay zones, voids, fissures and faults, depth to the bedrock and also examine the campaction of the weathered zone. Fourteen traverses each 240 m long oriented in the north to south with an inter-profile separations of 10 m were covered. Resistivity data were collected using the ABEM Terrameter SAS 4000 with the Wenner array and an electrode separation of 4 m. To cover the whole profile length, the roll-along technique was employed. Seismic data were collected using 10 Hz electromagnetic geophones with the ABEM Terraloc Mk.6, a 24 channel recording system. A full version of the RES2DINV software was used to obtain 2D inverse models of the resistivity data. The 2D resistivity data were collated and into 3D model of the subsurface. Seismic data was also processed with the ReflexW software into 2D velocity depth models unveiling three acoustic layers. P-wave velocity ranges of 699-870 m/s, 1189.1-1450.5 m/s and 3759-5321 m/s were recorded for the first, second and third layers respectively. The use of the 2D velocity depth models and the geoelectrical inverse models together with geologic information from the study area helped in the interpretations. Weak zones, distribution of the subsurface resistivity and possible voids were mapped with the resistivity method. The ii seismic method delineated the bedrock at depths > 20 m at the north which becomes close to the land surface at about 13 m at the south with p-wave velocity > 3759 m/s. The north and east display a highly compact weathered layer that can hold the weight of buildings but the south and part of the west cannot support the weight of buildings due to a highly weathered subsurface with low degree of compaction.
A thesis submitted to the Department of Physics, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of MASTER OF PHILOSOPHY.