P-wave and S-wave seismic refraction methods were used to investigate highway pavement failures at various locations on some highways in southeastern Nigeria. The locations are: 1) Ochon, on Obubra–Ikom Highway, 2) a bridge approach and Ikot-Abasi Eyop, both on Ikot-Ekpene–Umuahia Road, and 3) four locations on Calabar–Itu Highway. These highways traverse different geologic units, including sand, shale, marl, and claystone. The intercept-time method and Hagedoorn's Plus-Minus method were used in the analysis of the seismic data. Both the P- and S-wave methods generally delineated two layers, and in some locations a third layer. In combination, both types of surveys were employed to delineate and evaluate the quality and state of the subgrade at the failed locations, and at stable segments adopted as controls for the investigations. The qualities of the subgrades were evaluated based on elastic constants of Young's modulus, bulk modulus, and compressibility. Young's modulus values obtained for failed areas are less than that for stable segments of the highway adopted as controls for the study. Compressibility values follow the same trend, with lower values at the control locations and higher values at failed locations. Generally, the first layer stiffness parameters obtained for the failed segments had lower values than those for the stable segments.

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