Influence of petrophysical and geotechnical engineering properties on the electrical response of unconsolidated earth materials

We have investigated the influence of petrophysical and geotechnical engineering properties of unconsolidated near-surface geomaterials (soils) on their electrical responses or measurements. Complex resistivity measurements were performed at a constant effective stress on 32 samples of varying textures and compositions. Petrophysical and engineering properties that inherently affect the mechanical and strength behavior of the samples - that is, fines content, pore-size parameter, specific surface area, and fractal dimension of the grain-size distributions - were obtained from geotechnical analysis. The electrical parameters that describe the electrical response of the samples - that is, resistivity amplitude , phase shift , percent frequency effect (PFE), loss tangent tan δ, and the normalized phase N - are computed from the electrical measurements. Crossplots of the electrical and engineering parameters provide useful infor-mation on how the geotechnical properties of the soil material influence the electrical measurements. In particular, and tan δ values are strongly influenced by variations in the petrophysical and engineering properties (R²>0.60) in comparison with the other electrical parameters. Soils become more dissipative as their specific surface area increases. The PFE values are less sensitive (R²<0.55) to the petrophysical and engineering properties. Analysis of the correlations also indicates that characteristic or transitional values of the fines content (18%) and pore size (0.03 mm) exist, beyond which the phase and normalized phase values are insensitive to their respective increases. The characteristic value of 18% fines content is close to values reported in previous studies, which signifies transition in strength behavior of soils and, thus, such relations could be important in noninvasive strength assessment and monitoring of soils. Normalized phase values were used to assess the relative amount of fines in the studied soils.©2010 Society of ExplorationGeophysicists.

Duke Scholars

Author Fred K. Boadu Civil and Environmental Engineering