Application of Multichannel Analysis of Surface Waves (MASW) for Geotechnical Site Classification at a Proposed University Infrastructure Site, Awka

The expansion of academic and residential infrastructure at Nnamdi Azikiwe University, Awka, and its surroundings requires rigorous geotechnical site characterization to ensure safe and cost-effective foundation design. This study applies multichannel analysis of surface waves to determine shear wave velocity profiles and perform geotechnical site classification at a proposed infrastructure development site in Awka. MASW data were acquired at fifteen testing locations using a 24-channel seismograph connected to 4.5 Hz vertical geophones arranged at 2 m spacing, with a 10 kg sledgehammer source. Dispersion curves were extracted from the phase-velocity frequency domain using the phase shift transformation method and were inverted using a least-squares iterative approach to produce one-dimensional Vs profiles to 30 m depth. Shear wave velocities in the upper 5 m range from 145 to 310 m/s, reflecting the variability of the lateritic topsoil and compacted fill present across the site. Vs30 values at the fifteen test locations range from 190 to 420 m/s, corresponding to site classes C and D under NEHRP classification and EC8 ground types B and C, respectively. Areas with the lowest Vs30 values coincide with former flood channels identified in historical aerial photographs of the site. Two-dimensional lateral Vs sections constructed from spatially adjacent MASW profiles reveal subsurface heterogeneities that would not be captured by single-point testing methods. Recommendations for foundation type selection, footing depth, and soil improvement requirements are provided for each zone of the proposed development.

Keywords: MASW, shear wave velocity, Vs30, site classification, foundation design