Influence of Poisson's Ratio on Surface Wave Near-Field Effects

Surface waves measurements will be influenced by near-field effects when the source is located too close to the receiver array. These effects typically produce a reduction in the measured surface wave velocity. Since most surface wave inversion methods use a theoretical model that does not include near-field contributions, it is important that data are collected such that near-field effects are minimized. A recent study of theoretical and experimental data produced recommendations that the source should be located at least two wavelengths from the center of the receiver array to limit errors to less than 5%. However, this study was based on experiments and simulations using material with a Poisson's ratio of 0.3 to 0.33. In geotechnical applications, saturated conditions are often encountered where Poisson's ratio may approach values near 0.5. The objective of this study is to investigate the effect of high values of Poisson's ratio on the required source offset distance to minimize near-field effects. Results from simulations of simple but common profile conditions are presented and demonstrate that in some cases the source offset distance can be significantly lower than previously published values. Experimental data is also presented that support the findings.