Characterization of sub-surface structure, using seismic refraction and multi-channel analysis of surface waves methods in Ajere Ekori Yakurr LGA of cross river state

The study was to characterize the sub surface at Agere in Ekori, using seismic refraction method, multichannel analysis of surface waves technique and borehole intrusive technique. Data were collected using a 12channel seismograph and other accessories required for seismic refraction data collection. Software called seismicimager was used to examine the data. The primary wave velocity in the first layer varied from 690 m/s at 4.2 m to 96 m/s at 7.3 m. A Vp range of 315 m/s to 484 m/s at a depth of 2 m is present inside the layer and represents the organic soil constituents. A Vp range of 669 m/s to 1756 m/s represents loose sand (dry), loose made ground (rubble), landfill rubbish, disturbed soil, and clay landfill, all within a depth of 2.3 m to 12.1 m. In addition to the borehole intrusive method, multichannel analysis of surface wave (MASW) techniques was used to calculate the soil profile based on velocity. The source was a 7 kg sledge hammer, the detectors (receivers) were 24 units of 4.5 Hz geophones, and the recorder was a Terraloc Mark 8 ABEM. Seismicimager software was used for analysis. At Ajere 1 through 6, the MASW test configuration employed 5 m geophone spacing and a source offset distance of 5 m, while at Ajere 7, it used 1 m geophone spacing and a source offset distance of 2 m. Near the boreholes, all of the MASW test arrays were run. The trustworthy seismic data from Ajere 1 to 6 at depths of 0.7 m to 13.1 m and 4.7 m to 17 m. Based on SPT N values, the results showed that the shear wave velocities had been classified into three layers of soil: very soft, soft, and firm. The velocities below 164 m/s, between 164 and 190, and 190 m/s to 320 m/s were classified as these soil types. In the meantime, a drilling invasive technique based on SPT N value determines changes in the soil layer. Hard material shear wave velocity data was not provided. In conclusion, because of its non-destructive, non-invasive nature and relative speed of evaluation, the MASW technique has the potential to be adapted in soil study to complement intrusive technique.