Rock Failure and Instability from a Structural Perspective: Insights from the Shape Effect.

The failure and instability of a kind of specific rock structural bodies, such as the spalling-induced thin rock plates and the slender rock pillars, are the key inducing factors of rock engineering disasters and they are closely related to the shape effect, i.e., the height-to-width (H/W) ratio. For application in engineering practice, the strength characteristics and failure modes of the rock structural bodies when their H/W ratios vary in a wide range should be specially concerned, whereas this seems to be seriously ignored in previous studies. To support this purpose, a numerical scheme that integrates the statistical meso-damage constitutive model and the finite deformation formulation is proposed, to consider both the material failure and buckling instability of the rock structural bodies. The numerical results of a series of uniaxial compression tests of rock samples with relatively low H/W ratios (0.5–4) are completely consistent with the findings obtained from experiments. The behaviors of rock samples with high H/W ratios (6–28) show that the failure of rock samples is affected by both the H/W ratio and the strength of the rock material. That is, as the H/W ratio increases, the failure of rock samples gradually transforms from material failure dominated to structural (buckling) instability dominated, and the increase of the strength of rock material can facilitate this transition. The presented results have established an envelope about the failure and instability of rocks, and obtained the critical boundary line (CBL) for distinguishing different failure modes and determining the boundary between low and high H/W ratio. [ABSTRACT FROM AUTHOR]