Effect of insoluble materials on the volumetric behavior of rock salt

Abstract

This paper focuses on the presence of nodules of insoluble materials within salt specimens, and their effect on the volumetric strain measurements and the dilatancy phenomenon. We analyzed experimental results of over 120 conventional triaxial compression tests, and found that in 20% of the cases, the volumetric strain measurements were atypical. We also noted that the natural variability of the specimens can lead to a non-negligible data scattering in the volumetric strain measurements when different specimens are subjected to the same test. This is expected given the small magnitude of those strains, but it occasionally implies that the corresponding specimens are not representative of the volumetric behavior of the studied rock. In order to understand these results, we numerically investigated salt specimens modeled as halite matrices with inclusions of impurities. Simulations of triaxial compression tests on these structures proved that such heterogeneities can induce dilatancy, and their presence can lead to the appearance of tensile zones which is physically translated into a micro-cracking activity. The modeling approach is validated as the patterns displayed in the numerical results are identical to that in the laboratory. It was then employed to explain the observed irregularities in experimental results. We studied the natural variability effect as well and proposed a methodology to overcome the issue of specimen representativity from both deviatoric and volumetric perspectives.