LA FALLA DE LA ROCA

vírtually no infomation concerning the non-elastic behavior of hard rock is available. as the systems usually used to determine the strength of rock specimens become unstable as soon as the peak of the strain-stress characteristics is passed and its slope becomes negative. an analysis of the energy changes associated with the extensión of griffith cracks in tensión and compression is made. which shows that the non-elastic behavior can be described by a curved griffith locus in the strain-stress plane. only when the slope of this locus de ds>0, is a material intrinsically brittle and liable to spontaneous fracture. when dé ds<0. crack extensión can proceed by unstable fracture or stable failure. depending upon the amount of energy supplied to the material by the loading system. the effect of triaxial confinement is to reduce the negative slope of the griffith locus and make the material more ductile than it is in uniaxial compression. micro-seismic activity during the testing of rock specimen can be accounted for by assuming that rock is a heterogeneous material containing elastic inclusions. and analyzing the fracture of these inclusions in terms of the above. experimental data obtained from uniaxial compression tests on tennessee marble and saint cloud granite is presented and is shown to be in accord with the analytical predictions.