Instabilities and bifurcations in geomechanics

Abstract

This special issue of the International Journal of Numerical and Analytical Methods in Geomechanics (IJNAMG) contains nine selected papers based on presentations and discussions held at the International Workshop on Bifurcation and Degradations in Geomaterials (IWBDG 2008) in Lake Louise, Alberta, Canada, 28–31, May 2008. The venue offered an ideal setting for discussing the science and engineering in a relaxed atmosphere in the natural beauty of the Canadian Rockies. IWBDG 2008 is the eighth of a series of bifurcation workshops that started back in the early 1980s when the first International Workshop on Localization of Soils was organized in Karslrule, Germany, February 1988. This aroused so much enthusiasm and interest in the fundamental aspects of bifurcation theory for soils that a second workshop followed soon after in Gdansk, Poland, September 1989. The topic was then extended to rock mechanics at the third international workshop in Aussois, France, September, 1993. Interests grew steadily and the scope was expanded to instabilities and degradations in geomaterials at the fourth, fifth, sixth and seventh workshops that were held in Gifu, Japan, September 1997; Perth, Australia, November 1999; Minnesota, USA, June 2002 and Crete, Greece, June 2005. The collection of original papers in this special issue reflects the state-of-the-art in the specialized field of geomechanics, highlighting contemporary approaches to solving the central issue of failure within the framework of bifurcation theory. The papers include theoretical, numerical and experimental reports covering both diffuse and localized failures arising from a material (constitutive) instability phenomenon across various scales where force chains buckle as a microstructural instability to continuum-level instabilities in the form of shear banding. The special issue also broaches on a similar consideration of instability that relates to a possible bifurcation and loss of controllability in unsaturated soils. Professor Ioannis Vardoulakis, who tragically passed away in September 2009, played an eminent role in the development of bifurcation analysis in geomaterials, and as such was one of the founders of the IWBDG series. His substantial contributions, both technical and as a mentor to young researchers, were pivotal to the success of these workshops. We thus dedicate this special issue in Ioannis' memory for his pioneering contributions not only to the field of geomechanics, but also to the world of science and engineering. We trust this is a fitting tribute to an outstanding man and scientist. Finally, my sincere thanks go to all the authors who contributed to this issue, for which the manuscripts were fully peer-reviewed according to the rules of IJNAMG.