Determination of cross-anisotropic elastic constants of in situ soils using joint application of seismic refraction and downhole surveys

The precise determination of anisotropic elastic constants in natural soils is important for various geotechnical and geological engineering applications. This study presents a novel geophysical field approach for in situ measurement of these constants using the anisotropic components of P-wave and S-wave velocities. To achieve this, assuming cross-anisotropy in the soil deposits at a testing site, it was demonstrated that the propagation velocities of P- and S-waves in different directions and planes can be obtained through the joint application of seismic refraction and downhole surveys. The acquired refraction data were processed to calculate the velocities of the P-wave horizontal component (V_PH), S-wave vertical component (V_SV), and S-wave horizontal components (V_SH) using Seismic Refraction Tomography (SRT), Multichannel Analysis of Surface Rayleigh Waves (MASW), and Multichannel Analysis of Love Waves (MALW), respectively. Additionally, the velocities of vertical and oblique P-wave components (V_PV and V_Pθ) were determined by analyzing the arrival times and travel distances of signals collected from downhole testing. These velocity values were then integrated with rigorous equations derived from the theory of elastic wave propagation, enabling the quantification of elastic constants at the site. The developed approach may act as a valuable tool for the in situ estimation of cross-anisotropic elastic constants of shallow geomaterials based on field seismic techniques.