For heterogeneous rock specimen with initial random material imperfections in uniaxial plane strain compression, the effect of shear dilatancy on the failure process and stress-strain curve is numerically modeled using FLAC. For intact rock exhibiting linear strain-softening behavior beyond the occurrence of failure and then ideal plastic behavior, the failure criterion is a composite Mohr-Coulomb criterion with tension cut-off. Initial imperfection undergoes ideal plastic behavior beyond the occurrence of failure. The number of yielded elements within the specimen increases with dilation angle. Higher dilation angle causes no significant change in peak strength, slight changes to the post-peak stress-axial strain behavior, wider and steeper shear bands and more ductile stress-lateral strain curve in strain-softening stage because of the wider and steeper shear bands. At much higher dilation angle, the peak stress is slightly lower. It is possible that higher brittleness leads to earlier occurrence of failure. Strictly speaking, higher dilation angle leads to ductile post-peak stress-axial strain curve. This means that the contribution of the increase in shear band width exceeds the contribution of the increase in shear band inclination. The specimen with higher dilation angle has more apparent precursor to failure. The well-developed shear band inclination angle is closer to Arthur theory and is lower than Coulomb theory. Usually, Roscoe theory underestimates the well-developed shear band inclination angle unless dilation angle is much higher. At the same axial strain, higher dilation angle results in higher shear strain increment and higher volumetric strain increment in shear bands.


Geomaterials such as rock and soil are heterogeneous materials. In compression, with an increase of axial strain, microcracking may occur in the vicinity of material imperfections, such as voids, pores and cracks. Further loading will result in the progressive coalescence of microcracks to eventually form the macroscopic fractures (Scholz 1968).

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