Determination of elastic moduli and bearing capacity of sediments using geophysical and cone penetration test techniques in Yenagoa, Southern Nigeria

Abstract

In order to quantify the P-and S-wave velocities, dynamic elastic moduli and bearing capacity of shallow alluvial sediments, seismic refraction and cone penetration test (CPTu) soundings were carried out in two sites in Yenagoa. The seismic refraction data was analysed using the intercept-time technique to obtain the seismic velocities which were subsequently used to estimate the dynamic elastic moduli. The relevant CPTu data were emplaced into an established empirical equation to determine the shear wave velocity (V s ), with which the compressional wave velocity (V p ) was estimated. Combing the compressional and shear wave velocities, the dynamic elastic moduli of the shallow sediments were determined within the depth range of 0.5-8.0 m. On comparison, it was observed that the average values of V p and V s from the two methods are fairly in agreement. Significant difference in the average values was only observed in the dynamic elastic moduli. Correlation of the V s -wave and the dynamic moduli from the CPTu data show linear relationship between S-wave velocity and the dynamic elastic moduli with correlation coefficients (R 2 ) greater than 0.9 in all cases. These elastic moduli values can be used for the design of foundation of structures, site response and settlement analysis.

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

“…The p-wave and s-wave velocities have been found to be in semblance across the locations within the study area, with slight differences in the values most likely due to lateral variations in lithology composition. The values of p-wave and s-wave velocities obtained in this study are also consistent with the values of velocities obtained by Atat et al [1], Nwankwo et al [25] and Bayo et al [9] from refraction analyses carried out in their previous works in the eastern and central Niger Delta.…”

“…Values of unity or less for the ratios indicate the presence of air in the soil, which weakens the soil considerably. Again, the values of the moduli and their ratios reported in this study are consistent and comparable to the values obtained from the seismic refraction analyses carried out by Bayo et al [9] around the same study area. Finally, the lamdarho (Lame's attribute) λρ is sensitive to the presence of fluid especially gas in weak porous media.…”

“…This also supports the fact that the engineering strength or vulnerability of the soil varies laterally from one location to another. Similarly, the seismic refraction survey carried out by Bayo et al [9] around Yenagoa in Bayelsa State, central Niger Delta, reveals the topsoil to be made up of well consolidated and competent geomaterials. They found that Poisson ratio around Yenagoa lies between 0.232 and 0.239, 0.234 and 0.235 and between 0.235 and 0.242 across the sites surveyed.…”

“…Table 1 shows the quantitative values of the elastic properties and attributes we obtained from the various mathematical relations, giving us clear information on the engineering strength of the soil. Table 2 obtained from Sheriff and Geldart [10] and Bayo et al [9] enabled us to determine the competence of the geomaterial of the topsoil in the study area.…”

“…The values of Vp, Vs, Vp/Vs, Poisson ratio, rigidity and incompressibility they obtained showed that the soil under study was porous, air-filled, anisotropic and had poor engineering strength. Bayo et al [9] carried out a similar refraction survey in Yenagoa and its environs, South-south, Nigeria and found, based on the quantitative values of the elastic parameters obtained in the study area, that the topsoil was made up of competent geomaterials. In particular, the values of the Poisson ratio they obtained lie within the 0.25 range and Vp/Vs was within the 1.7 range.…”