Breakage and shear behaviour of intermittent rock joints

Abstract The breakage and shear behaviour of intermittent rock joints have been investigated in a series of direct shear tests with a new shear device, specifically designed for this purpose. The tests have been performed on specimens of rock-like material or hard rock, respectively, incorporating idealized non-persistent joints, made up of a number of short cracks in an en-echelon arrangement along the central shear axis. The shear behaviour of such a joint constellation has been found to be composed of different phases. The first phase of shearing is that of the actual rupture, initiated by the formation of wing cracks, starting from the existing cracks and growing into the material bridges, and concluded by the generation of additional new fractures connecting the initial cracks in the zone between the wing cracks. The second phase of shearing is characterized by friction processes and volume increase in the then continuous shear zone. Finally, the third phase of shearing, reached after large shear displacements, is determined by sliding processes inside the strongly fractured shear zone. In a large number of shear tests the geometrical parameters of the discontinuous joints as well as the loading conditions have been found to influence the activated shear resistance in each phase of shearing to a noticeably different extent. The orientation of the initial cracks and the normal stress, however, have been identified as the most influential parameters. Depending on the test conditions, an initially discontinuous rock joint can activate the largest shear resistance not just before rupture but in one of the two subsequent phases of shearing as well. The mechanisms which govern the different shear phases could be identified as (1) tensile rupturing, (2) rolling and sliding friction of dilatant joint zones and (3) sliding within the joint filling composed of brecciated material.

[1]  J. C. Jaeger.  Friction of Rocks and Stability of Rock Slopes , 1971 .

[2]  Jayantha Kodikara,et al.  Shear behaviour of irregular triangular rock-concrete joints , 1994 .

[3]  B. Ladanyi,et al.  Simulation Of Shear Behavior Of A Jointed Rock Mass , 1969 .

[4]  B. J. Carter,et al.  Simulation of crack growth and interaction in compression , 1995 .

[5]  Antonio Bobet,et al.  Coalescence of multiple flaws in a rock-model material in uniaxial compression , 2002 .

[6]  Ove Stephansson,et al.  Modification of the G-criterion for crack propagation subjected to compression , 1994 .

[7]  Yijun Du,et al.  THE INSTABILITY OF EN-ECHELON CRACKS AND ITS PRECURSORS , 1986 .

[8]  S. Nemat-Nasser,et al.  Brittle failure in compression: splitting faulting and brittle-ductile transition , 1986, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[9]  Herbert H. Einstein,et al.  Coalescence of fractures under shear stresses in experiments , 1995 .

[10]  K. T. Chau,et al.  Analysis of crack coalescence in rock-like materials containing three flaws—Part I: experimental approach , 2001 .

[11]  Evert Hoek,et al.  Practical estimates of rock mass strength , 1997 .

[12]  M. H. de Freitas,et al.  LABORATORY TESTING AND PARAMETERS CONTROLLING THE SHEAR STRENGTH OF FILLED ROCK JOINTS , 1993 .

[13]  Antonio Bobet,et al.  Fracture coalescence in rock materials : experimental observations and numerical predictions , 1997 .

[14]  Michael E. Plesha,et al.  An investigation of the mechanics of rock joints—Part I. Laboratory investigation , 1993 .

[15]  M. H. Freitas,et al.  Mechanisms of shear failure in artificial fractures of sandstone and their implication for models of hydromechanical coupling , 1993 .

[16]  F. Patton.  Multiple Modes of Shear Failure In Rock , 1966 .

[17]  A. Haque,et al.  Shear behaviour of idealized infilled joints under constant normal stiffness , 1999 .

[18]  Jon E. Olson,et al.  The initiation and growth of en échelon veins , 1991 .

[19]  B. Stimpson,et al.  Failure of slopes containing discontinuous planar joints : Proc 19th US Symposium on Rock Mechanics, Stateline, Nevada, 1–3 May 1978, V1, P296–300. Publ Reno: University of Nevada, 1978 , 1979 .

[20]  Development of subcracks betweenen echelon fractures in rock plates , 1995 .

[21]  K. T. Chau,et al.  Crack coalescence in a rock-like material containing two cracks , 1998 .

[22]  Herbert H. Einstein,et al.  Fracture coalescence in rock-type materials under uniaxial and biaxial compression , 1998 .

[23]  D. Pollard,et al.  Progress in understanding jointing over the past century , 1988 .

[24]  Gregory B. Baecher,et al.  The effect of discontinuity persistence on rock slope stability , 1983 .

[25]  R. Wong,et al.  The coalescence of frictional cracks and the the shear zone formation in brittle solids under compressive stresses , 1997 .

[26]  H. H. Einstein,et al.  The Probabilistic Model For Shearing Resistance Of Jointed Rock , 1978 .

[27]  H. Honi,et al.  Brittle Failure in Comression : Splitting Faulting and Brittle-Ductile Transition , 1986 .