Development and verification of a micromechanics-based continuum theory for long-term deterioration of hard rock

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The purpose of this study is to establish a micromechanics-based continuum damage model to analyze short- and long-term behavior of brittle rocks under compression. The model developed in this study provides information on not only the macroscopic mechanical responses of rock such as strength, but also microscopic information such as crack lengths and crack density during inelastic deformation. A small number of parameters are involved in this model and can be identified from the results of triaxial compression tests, creep tests and microscopic observation of microcracks. The model is derived from the mechanics of tensile microcracks. It is assumed that local tensile stress thereby sliding up on asperities causes microcracks growth. By generalizing the analysis of one single microcrack and also, including the effects of interaction among neighboring microcracks directly on cracks growth, the proposed model for brittle rocks under compression is derived.In order to illustrate the predi … More ctive capability of the proposed model, the model is applied to simulation of short-term mechanical tests of Inada granite. Numerical results are compared with experimental data from triaxial compression tests results and microscopic observations of microcracks. The peak stress obtained numerically is in good accordance with the one observed in triaxial compression tests under a confining pressure higher than 10 MPa.Furthermore, the present model is capable of reproducing the three characteristic stages of long-term behavior commonly observed in laboratory creep tests. The sub-critical microcrack growth parameters can be determined for Inada granite by fitting the numerical results of elapse time to failure versus the creep stress ratio curve with the experimental data under both dry and wet conditions. Use of the extended model makes it possible to analyze not only the extension of microcrack length, but also the development of the excavation damage zone around tunnels as a function of time. Less