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SUMMARY:Propagation of Frictional Discontinuities
DTSTART:20121129T121500
DTEND:20121129T131500
DTSTAMP:20260920T164839Z
UID:ffb318a4e86ff3943752a04eb8c9ac96dc14e3ea23ce202a7b6ae89d
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Antonio Bobet\nThe most important mechanism for deformat
 ion and failure in rock masses under relatively low stresses is slip along
  pre-existing discontinuities. As stresses increase relative to the streng
 th of the rock (e.g. in very deep tunnels\, open mine excavations\, faults
 \, etc.)\, failure through discontinuities as well as through the rock mat
 rix becomes possible. The failure involves a complex mechanism of interact
 ion between existing discontinuities\, creation of new discontinuities\, a
 nd coalescence.\nIn rocks\, there is the tendency of cracks to initiate an
 d propagate in tension due to the lower toughness of the material in tensi
 on than in shear. This initiation mechanism however may not be favored whe
 n predominant stresses are compressive. In compression\, two types of crac
 ks can be generated from a pre-existing discontinuity (flaw): wing or prim
 ary cracks and secondary cracks. Wing cracks are tensile cracks that initi
 ate 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 recognize
 d as shear cracks. There are two possible directions for shear crack initi
 ation: coplanar and oblique to the flaw. Crack coalescence through wing (t
 ensile) cracks is just one possible mode of crack linkage\, which occurs o
 nly with small confining stresses and for a particular flaw distribution. 
 Coalescence through shear cracks is observed under a variety of flaw distr
 ibutions\, and is the only possible mechanism for crack linkage under mode
 rate to large confinement. Propagation along a shear crack requires not on
 ly the creation of new surfaces\, similar to what happens with tensile cra
 cks\, but also slip along the new surfaces. The mechanism for slip initiat
 ion is controlled by the strength drop required for the transition from pe
 ak to residual along the newly formed shear crack and on the displacement 
 necessary for such transition. Laboratory experiments show that the mode I
 I critical stress intensity factor is not a material property\, as it stro
 ngly depends on confinement.\n\nBio: Dr. Bobet is a Professor of Civil Eng
 ineering at Purdue University\, USA. He holds a bachelor degree in Civil E
 ngineering from Technical University of Madrid in Spain and a Doctor of Sc
 ience degree from Massachusetts Institute of Technology\, USA. Dr. Bobet
 ’s areas of interest include rock mechanics\, underground structures\, s
 oil-structure interaction during seismic events and problem soils. He has 
 extensive experience in practice. He was senior geotechnical engineer at E
 uroestudios\, consulting engineers\, in Spain for four years\, and a const
 ruction manager for Ferrovial\, Spain\, also for four years.\nHe has autho
 red 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 Me
 chanics and Rock Engineering Journal\, and Tunnelling and Underground Spac
 e Technology Journal. He is a member and past chair of the ASCE rock mecha
 nics committee\, a Director of the Board of Directors of the American Rock
  Mechanics Association (ARMA)\, the co-chair of the Working Group on Sugge
 sted Methods for Failure of Intact Rock\, appointed by the International S
 ociety of Rock Mechanics\, and the Chair of the 2012 U.S. Rock Mechanics/G
 eomechanics Symposium. He is currently the Vice-president of the American 
 Rock Mechanics Association. Dr. Bobet has received a number of awards\, in
 cluding the 2011 Ralph B. Peck Award from ASCE\, the 2012 National Award f
 or Significant Contributions in Science and Technology - SENACYT Panama\, 
 and the 2012 ARMA Research Award.
LOCATION:GC C330
STATUS:CONFIRMED
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