Chapter 8: Estimating In Situ Horizontal Stress in Soil Using Time-lapse VS Measurements
Ranajit Ghose, 2010. "Estimating In Situ Horizontal Stress in Soil Using Time-lapse VS Measurements", Advances in Near-surface Seismology and Ground-penetrating Radar, Richard D. Miller, John H. Bradford, Klaus Holliger
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The magnitude and temporal changes of in situ horizontal stress at shallow depths in the subsoil are crucial information in geotechnical engineering. Although various methods of monitoring in situ horizontal stress have shown some success, such monitoring remains extremely challenging, especially for sands and stiff clays, and large uncertainties are usual. Laboratory experiments are performed that involve realistic values of stress and porosity, combined with seismic-array data acquisition, to monitor changes in shear-wave velocity (VS) induced solely by changes in horizontal stress. Seismic-array data have been instrumental in distinguishing the small velocity changes associated with horizontal stress changes. Stress-porosity empirical models and micromechanical models have predicted quite accurately the observed trend of variation in VS as a function of horizontal stress. This trend is unique for a given combination of vertical stress, porosity, and soil type. Therefore, by monitoring the temporal change of VS by means of a seismic receiver array fixed at a given depth range and then by using the velocity–horizontal stress trend predicted by the model, one can estimate the temporal change and magnitude of in situ effective horizontal stress. A data-driven inversion approach has been tested on laboratory-experiment data for which the effective horizontal stress is known. The results demonstrate the possibility of estimating in situ effective horizontal stress at a given depth in subsoil, with an uncertainty of less than 15–20%, even when the porosity, vertical stress, and field factor are unknown. This approach shows potential for use on real field data.