Abstract:

To reveal the physical and mechanical characteristics of impure salt rock, especially the mechanism of splitting fracture under high confining pressure, the test-matrix consisting of chemical components analysis, SEM (scanning electron microscope), uniaxial and conventional tri-axial compression tests has been carried out. The experimental results and theoretical analysis revealed that: the main components of impurities in salt rock, which distribute with dotted pattern inner big grains or with agglomerate and banded patterns among grains, are glauberite and anhydrite and some argillaceous minerals. On micro-size, the impurities mainly distribute among salt grain boundaries or act as the cement matrix of salt grains. The presence of impurities will, in turn, a certain extent increase the strength and reduce the flexibility of the salt rock, for which the meso-mechanism can be explained as impurities have modified the mechanical properties of the boundaries among adjoined halite grains so that the self-heal ability will be of some reduction. Compared to the pure salt rock, impurities can cause more unrecoverable damage to accumulate under tri-axial compression tests. Different with the main distributed impurities, uneven distributed impurities tend to cause uncoordinated deformation and local fracture. Moreover, in the final phase of strain-hardening under high confining pressure tests, the uneven distributed impurities may even cause the membrane's damage in local fracture regions and then induce the sample's splitting fracture and "stress-drop" phenomenon. The "stress-drop" can be simply explained by criterion of Mohr-Coulomb. The research above has indicated some influence of impurities on salt rock and also made some references for the further study of impure salt rock and reasonable stability investigations of the storage caverns in salt rock formation.

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