Chapter 24: Clayey Landslide Investigations Using Active and Passive VS Measurements
F. Renalier, G. Bièvre, D. Jongmans, M. Campillo, P.-Y. Bard, 2010. "Clayey Landslide Investigations Using Active and Passive VS Measurements", Advances in Near-surface Seismology and Ground-penetrating Radar, Richard D. Miller, John H. Bradford, Klaus Holliger
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Clay slopes frequently are affected by gravitational movements. Such movements generate complex patterns of deformation that have slip surfaces located at different depths and are likely to modify geophysical parameters of the ground. Geophysical experiments performed on the large clayey Avignonet landslide (Western Alps, France) have shown that shear-wave velocity (VS) is most sensitive to clay deconsolidation resulting from the slide. Values of VS at shallow depths exhibit an inverse correlation with the GPS-measured surface-displacement rates. Compared with measurements in stable zones, VS values in the most deformed areas of the slide can be reduced by a factor of two to three. Laboratory measurements on clay samples set in triaxial cells have shown that a strong decrease of VS values accompanies an increase in the void ratio, in a velocity range similar to that measured in situ. Although other factors (stress change, cementation, granularity) can modify VS values, these results justify the potential of VS imaging to map spatially the deformation induced by a landslide. Several active and passive techniques for measuring VS are tested and compared on the kilometer-size and 50-m-deep Avignonet landslide. The crosscorrelation technique, applied to seismic noise recorded by a large-aperture array and associated with shot records, turns out to be an effective tool for imaging the landslide in three dimensions. If permanent stations are installed, the same method also can be used to monitor the evolution of seismic velocity with time, as an indicator of landslide activity.
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Near-surface seismology and ground-penetrating radar (GPR) have enjoyed success and increasing popularity among a wide range of geophysicists, engineers, and hydrologists since their emergence in the latter half of the twentieth century. With the common ground shared by near-surface seismology and GPR, their significant upside potential, and rapid developments in the methods, a book bringing together the most current trends in research and applications of both is fitting and timely. Conceptually, near-surface seismology and GPR are remarkably similar, and they share a range of attributes and compatibilities that provides opportunities to integrate processing and interpretation workflows, which makes them a perfect pair to share pages in a book.
With growth in numbers and professional emphasis have come sections, focus groups, and even professional societies specifically promoting near-surface geophysics. The emergence of near-surface geophysics groups, beginning in the late 1990s and extending into the early twenty-first century, has fueled a diversity of opportunities for professional collaborations. A range of workshops and shared publications has been the fruit of collaborative efforts. The near-surface community continues to extend and develop methods and approaches necessary to satisfy increasing demands in some of the socioeconomically pertinent disciplines such as civil and environmental engineering and hydrology. This book represents the first formal cooperative effort undertaken by the near-surface communities of the Society of Exploration Geophysicists, the American Geophysical Union, and the Environmental and Engineering Geophysical Society.