ABSTRACT
Results of an investigation into the effects of drying and wetting cycles, on the shear strength of discontinuities, in natural argillaceous shales are presented. Shear strength in natural discontinuities was measured by triaxial and direct shear testing. Mohr-Coulomb shear strength envelopes were established for all wetting and drying cycles applied. After several cycles of drying and wetting the structure and geometry of the sample is lost, turning it into a particulate soil. This new material (particulate soil) was also tested to obtain a lower limit of resistance values. The results show that argillaceous rocks exhibit a big reduction in resistance when they are subjected to successive cycles of wetting and drying. Using a mineralogical analysis, it was found that the effect of degradation, caused by wetting and drying cycles, in the composition and proportions of the main chemical compounds of the rock, is not important. It revealed that the successive cycles of wetting and drying generates a physical degradation that takes place in very short periods of time and causes a considerable reduction of resistance that could explain the failure of natural deposits of these materials when they are exposed to atmospheric environmental changes.
