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Abstract For heterogeneous rock specimen with smooth ends and initially random material imperfections in uniaxial plane strain compression，the effects of loading velocity on the failure process are modeled using FLAC. A few coded FISH functions are used to prescribe the random imperfections and to remember the number of failed elements. For intact rock exhibiting linear strain-softening behavior after the occurrence of failure and then ideal plastic behavior，the failure criterion is a composite Mohr-Coulomb criterion with tension cut-off. Imperfection undergoes ideal plastic behavior after the occurrence of failure. As loading velocity increases，the peak stress and corresponding axial strain increase；and the post-peak stress-axial strain curve becomes less steep. In the loading process，the number of failed elements per 10 time steps-axial strain curve possesses three stages with remarkable increase in the failed elements. At higher loading velocities，the second and third stages become wider；the peak of the second stage decreases，and the peak of the third stage increases. In the initially loading stage and before the failure of all imperfections，the number of failed elements-axial strain curve is less steep at higher loading velocities. Since the crack propagation and the stress transfer within the specimen are less sufficient at higher loading velocities，when axial strain is less than a certain value，the number of yielded elements can be lower at the same axial strain. It is found from the number of failed elements-axial strain curve that the specimen loaded at higher loading velocities is subjected to more severe failure in the final deformational stage.
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Received: 20 April 2007
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