A Computer-Aided Algorithm Combined with an Integrated Downhole Method to Improve Shear Wave Detection and Damping Ratio Assessment: Theory and Preliminary Results

Abstract

This contribution introduces a computerized semi-automated procedure coupled with a dedicated algorithm to improve shear wave velocity assessment and the on-site elastic damping ratio estimation of ground materials. The standard equipment of the downhole method is integrated with a horizontal geophone (guardian) placed on the field surface. Mask tapering and band multi-filter functions improve first arrival, recognizing and isolating SH-wave trains to estimate damping ratio profiles. These are computed by treating signals using a frequency–time combined approach (frequency–time packets method). The signals are corrected to consider the different source pulse amplitude, the effects of the propagation path, and scattering. The damping ratio profile is statistically computed in terms of the local drift of trend on the amplitude ratio series that would otherwise have a normal distribution centered on zero. These profiles intercept the lithology changes in the test sites and meet the damping values stemming from previous field tests and the laboratory experimental tests available in the literature regarding materials such as the ones investigated here.

Keywords

• ground material damping ratio
• downhole test
• frequency–time signal analysis
• seismic signals processing
• shear wave