A Study On The Scale Effects And Representative Elemental Volume(REV) Of Strength And Deformation Characteristics For Fractured Rock Masses

This paper focuses on scale effects and representative elemental volume(REV) of strength and deformation characteristics for rock masses with random intermittently joint. Both the equivalent strength and the equivalent deformation characteristics are studied, one of which start through the parameters of rock masses–cohesion and frictionfactor, the other of which is in research by plotting stress-strain curve. The main contents are as follows:1. It's summarized that the present numerical method of research in jointed rock masses, the characteristics of equivalent continuum approach, and the principle of equivalent strength approach. Besides it's introduced that geological character of joint, including geometry,mechanics,statistics and so on.2. A series of numerical specimens are conducted with random simulation method, which represent the fracture networks based on fracture geometry information3. Based on specimens of rock masses with random intermittently joint, the strength is confirmed with the principle of equivalent strength method. Cohesion and friction degree are obtained by the method of the least squares fitting.4. There is high negative correlations between, the equivalent strength parameters, cohesion and friction-factor, which are to the rock specimens with the same scale and joint probability model. The results show that the strength parameters must be as relative variables for calculating the reliability of Geotechnical Engineering.5. The effects of space between fractures on the equivalent strength parameters are studied, between which a empirical equation for the relationship is concluded.6. A theoretical model of size effect of uniaxial and triaxil compression strength is brought out. The error of regression is tiny. And this part discusses the REV of axial strength, which is the value of size when the strength is basically constant with the increase of size of square models.7. The scale effects and REV of strength parameters are studied in this paper.8. The effects of space between fractures on REV of the equivalent strength parameters are studied, which is fitted very well by power equation y = a+bxc. The REV of cohesion is more sensitivity than that of Friction-factor for space between fractures.9. The effects of trace lengths of fractures on REV of the equivalent strength parameters are studied, which is fitted very well by power equation y = a+bxc. The REV of cohesion is increase with the increase of size lengths of models, while REV of Friction-factor is inverse.10. Despite REV of rock masses ,it is anisotropy, which is concluded in this paper11. Under the confining pressure condition, the model with the same size and the probability model of joint are loaded till failure, by which the stress-strain curve can be ploted. The curve can reflect the scale effect of jointed rock mass. The results show that the deformation curves are scattered for the small size specimens, and the scattering of the curves clearly narrows down with increase of the side lengths.It proves than there is scale effect in the stress-strain curves, so the representative element volume(REV) of jointed rock mass can be obtained.