Numerical studies of the influence of microstructure on rock failure in uniaxial compression - Part II: Constraint, slenderness and size effect

Numerical simulations of uniaxial compression have been conducted to evaluate the effects of the loading system and specimen geometry on the deformation and failure behavior of brittle and heterogeneous rock. This was done using the Rock Failure Process Analysis program (RFPA(2D)). Numerical model specimens with different Young's modulus ratios of platen to specimen (Ep/Es = 0, 0.1, 1, 2, and 10). different slenderness in terms of height to width ratios (H/W=0.5, 0.67, 1, 1.5, and 3), and different sizes (H x W = 30 x 20, 100 x 67, 120 x 80, 150 x 100, and 190 x 127 mm) have been numerically analyzed. The numerical simulations not only qualitatively reproduce the experimentally observed pre- and post-peak failure phenomena of the loaded specimens. but also provide a quantitative evaluation of the influence of the parameters studied on the complete stress-strain curves and the strength characteristics. The results presented here indicate that a more ductile response is simulated and the peak strength increases when the end constraint increases. The crack patterns show that almost-vertical splitting cracks develop in specimens loaded with softer loading platens, and the well-known hour-glass failure mode develops in specimens loaded with stiffer loading platens. The peak stress sustained by a specimen decreases with increasing slenderness of the specimen. The pre-peak portion of the stress-strain curves shows no significant dependence on slenderness; however, the post-peak curves are highly dependent on the ratio of specimen height to width. As far as the effect of size is concerned, numerical results reveal a strength reduction with an increase in specimen size, whereas the change of the specimen size does not obviously change the failure patterns. (C) 2000 Elsevier Science Ltd. All rights reserved.