Evaluation of Geotechnical Parameters and Attributes of Amassoma Soil in Bayelsa State, South-south, Nigeria, Using Seismic Refraction Analysis as an Indicator for Its Engineering Strength Determination

Abstract

In this paper, we have carried out analysis of seismic refraction data obtained from two locations around Amassoma and its environs in Bayelsa State, South-South, Central Niger Delta, Nigeria. The core objective of the study was to evaluate the elastic parameters and attributes of the soil and its geotechnical conditions in order to determine its soil strength to carry load . These geophysical parameters and attributes include the p-wave and s-wave velocities, Vp /Vs ratio, dynamic Poisson ratio σ, rigidity modulus μ, bulk incompressibility K, Young’s modulus E, lamda-rho (lame’s) attribute λρ, K/μ ratio, and E/μ ratio. The layer velocities were obtained as the inverse of the slope of the travel time versus geophone distance curves plotted with the available refraction data, while the layer thicknesses were obtained from the intercepts of the plots. The p-wave and s-wave velocities were used as inputs in various mathematical relations to obtain the elastic moduli and their ratios. The results obtained depict a two-layer model, with the mean p-wave velocities of the layers generally found to lie in the 218m/s - 392m/s range and mean s-wave velocities in the 128m/s -231m/s range. The Vp/Vs ratio (the lithology discriminator) has values lying between 1.699 and 1.7 and the dynamic Poisson ratio has values between 0.235 and 0.240 . The moduli have most of their values above 3.0 x 107 N/m2 and their ratios are clearly more than unity. Overall, these results show that the topsoil and underlying sediments in the study area which are composed mainly of clay and sandy clay can be described as well consolidated and competent geomaterials that can support foundation structures and loads placed on them. In the final analysis, all the results obtained were found to be in agreement with the values reported in the literature for the Niger Delta and across the globe. The seismic refraction method has therefore been shown in this study as an effective technique for assessing the geotechnical strength of the soil.