A non-associated viscoplastic model for the behaviour of granite in triaxial compression

Experimental work and analytical modelling were applied to study the elastic-viscoplastic behaviour of a Japanese granite rock. Triaxial creep tests, at confining pressure varying from 0 to 40 MPa, were performed following a step-wise loading procedure. which emphasises the transient creep behaviour. A non-associated constitutive equation was then formulated, which describes their elastic and viscoplastic properties during any compressive state this model is based on the theory proposed by Cristescu (see review in N.D. Cristescu, U. Hunsche, Time Effects in Rock Mechanics, Wiley, New York. 1998). The constitutive functions have been entirely determined from the available experimental data. In this paper, no assumption concerning the existence of the viscoplastic potential is made. The flow rule is defined by a function which denotes the orientation of the viscoplastic strain rate tenser. The model prediction is compared with the experimental data following different stress paths. The results are qualitatively very good throughout all the stress conditions, and enable the model to be applied to various engineering problems. (C) 2001 Elsevier Science Ltd. All rights reserved.