Fabric evolution and crack propagation in salt during consolidation and cyclic compression tests

Abstract

It is of great interest to describe and quantify the evolution of microstructure for a better understanding of rock deformation processes. In this study, 2D microstructure images of salt rock are analyzed at several stages of consolidation tests and cyclic compression tests to quantify the evolution of the magnitude and orientation of solidity, coordination, local solid volume fraction, and crack volume. In both the consolidation and the cyclic compression tests, the deformation of aggregates achieved by grain rearrangement is greater than that achieved by the deformation of an individual grain. In the consolidation test, the aggregates are rearranged into horizontal layers of coordinated grains, the orientation distribution of grain indentations is quasi-uniform, and the size of the pores reduces and becomes more uniformly distributed. As a result, salt rock microstructure becomes more homogeneous. The increase in local solid volume fraction in the lateral direction is correlated with an increase in the oedometer modulus. In the cyclic compression tests, grain-to-grain contact areas decrease due to the redistribution of grains and the propagation of intergranular cracks. Aggregates are reorganized into columns of coordinated grains. Intergranular opening-mode cracks tend to develop in the axial direction, while intergranular shear-mode cracks propagate preferentially in the lateral direction. The lateral components of the fabric tensors of coordination and local solid volume fraction decrease, which result in an increase in the Poisson’s ratio. The fabric descriptors used in this work allow a better quantification and understanding of halite deformation processes and can be used in other types of rocks encountering similar deformation mechanisms.