Propagation of Frictional Discontinuities
Event details
| Date | 29.11.2012 |
| Hour | 12:15 › 13:15 |
| Speaker | Prof. Antonio Bobet |
| Location |
GC C330
|
| Category | Conferences - Seminars |
The most important mechanism for deformation and failure in rock masses under relatively low stresses is slip along pre-existing discontinuities. As stresses increase relative to the strength of the rock (e.g. in very deep tunnels, open mine excavations, faults, etc.), failure through discontinuities as well as through the rock matrix becomes possible. The failure involves a complex mechanism of interaction between existing discontinuities, creation of new discontinuities, and coalescence.
In rocks, there is the tendency of cracks to initiate and propagate in tension due to the lower toughness of the material in tension than in shear. This initiation mechanism however may not be favored when predominant stresses are compressive. In compression, two types of cracks can be generated from a pre-existing discontinuity (flaw): wing or primary cracks and secondary cracks. Wing cracks are tensile cracks that initiate at or near the tips of a flaw and propagate in a stable manner towards the direction of maximum compression. Secondary cracks initiate from the tips of the flaws, propagate in a stable manner, and have been recognized as shear cracks. There are two possible directions for shear crack initiation: coplanar and oblique to the flaw. Crack coalescence through wing (tensile) cracks is just one possible mode of crack linkage, which occurs only with small confining stresses and for a particular flaw distribution. Coalescence through shear cracks is observed under a variety of flaw distributions, and is the only possible mechanism for crack linkage under moderate to large confinement. Propagation along a shear crack requires not only the creation of new surfaces, similar to what happens with tensile cracks, but also slip along the new surfaces. The mechanism for slip initiation is controlled by the strength drop required for the transition from peak to residual along the newly formed shear crack and on the displacement necessary for such transition. Laboratory experiments show that the mode II critical stress intensity factor is not a material property, as it strongly depends on confinement.
Bio: Dr. Bobet is a Professor of Civil Engineering at Purdue University, USA. He holds a bachelor degree in Civil Engineering from Technical University of Madrid in Spain and a Doctor of Science degree from Massachusetts Institute of Technology, USA. Dr. Bobet’s areas of interest include rock mechanics, underground structures, soil-structure interaction during seismic events and problem soils. He has extensive experience in practice. He was senior geotechnical engineer at Euroestudios, consulting engineers, in Spain for four years, and a construction manager for Ferrovial, Spain, also for four years.
He has authored or co-authored more than one hundred technical publications. He serves or has served on the Editorial Board of ASCE Journal of Geotechnical and Geoenvironmental Engineering, ASTM Geotechnical Testing Journal, Rock Mechanics and Rock Engineering Journal, and Tunnelling and Underground Space Technology Journal. He is a member and past chair of the ASCE rock mechanics committee, a Director of the Board of Directors of the American Rock Mechanics Association (ARMA), the co-chair of the Working Group on Suggested Methods for Failure of Intact Rock, appointed by the International Society of Rock Mechanics, and the Chair of the 2012 U.S. Rock Mechanics/Geomechanics Symposium. He is currently the Vice-president of the American Rock Mechanics Association. Dr. Bobet has received a number of awards, including the 2011 Ralph B. Peck Award from ASCE, the 2012 National Award for Significant Contributions in Science and Technology - SENACYT Panama, and the 2012 ARMA Research Award.
In rocks, there is the tendency of cracks to initiate and propagate in tension due to the lower toughness of the material in tension than in shear. This initiation mechanism however may not be favored when predominant stresses are compressive. In compression, two types of cracks can be generated from a pre-existing discontinuity (flaw): wing or primary cracks and secondary cracks. Wing cracks are tensile cracks that initiate at or near the tips of a flaw and propagate in a stable manner towards the direction of maximum compression. Secondary cracks initiate from the tips of the flaws, propagate in a stable manner, and have been recognized as shear cracks. There are two possible directions for shear crack initiation: coplanar and oblique to the flaw. Crack coalescence through wing (tensile) cracks is just one possible mode of crack linkage, which occurs only with small confining stresses and for a particular flaw distribution. Coalescence through shear cracks is observed under a variety of flaw distributions, and is the only possible mechanism for crack linkage under moderate to large confinement. Propagation along a shear crack requires not only the creation of new surfaces, similar to what happens with tensile cracks, but also slip along the new surfaces. The mechanism for slip initiation is controlled by the strength drop required for the transition from peak to residual along the newly formed shear crack and on the displacement necessary for such transition. Laboratory experiments show that the mode II critical stress intensity factor is not a material property, as it strongly depends on confinement.
Bio: Dr. Bobet is a Professor of Civil Engineering at Purdue University, USA. He holds a bachelor degree in Civil Engineering from Technical University of Madrid in Spain and a Doctor of Science degree from Massachusetts Institute of Technology, USA. Dr. Bobet’s areas of interest include rock mechanics, underground structures, soil-structure interaction during seismic events and problem soils. He has extensive experience in practice. He was senior geotechnical engineer at Euroestudios, consulting engineers, in Spain for four years, and a construction manager for Ferrovial, Spain, also for four years.
He has authored or co-authored more than one hundred technical publications. He serves or has served on the Editorial Board of ASCE Journal of Geotechnical and Geoenvironmental Engineering, ASTM Geotechnical Testing Journal, Rock Mechanics and Rock Engineering Journal, and Tunnelling and Underground Space Technology Journal. He is a member and past chair of the ASCE rock mechanics committee, a Director of the Board of Directors of the American Rock Mechanics Association (ARMA), the co-chair of the Working Group on Suggested Methods for Failure of Intact Rock, appointed by the International Society of Rock Mechanics, and the Chair of the 2012 U.S. Rock Mechanics/Geomechanics Symposium. He is currently the Vice-president of the American Rock Mechanics Association. Dr. Bobet has received a number of awards, including the 2011 Ralph B. Peck Award from ASCE, the 2012 National Award for Significant Contributions in Science and Technology - SENACYT Panama, and the 2012 ARMA Research Award.
Practical information
- General public
- Free
Organizer
- Prof. Nikolas Geroliminis & Prof. Katrin Beyer
Contact
- Prof. Lyesse Laloui