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In simulation of fractured rock mass such as mechanical calculation, hydraulic calculation or coupled hydro-mechanical calculation, the representative element volume of fractured rock mass in the simulating code is very important and give the success of simulation works. The difficulties of how to make a representative element volume are come from the numerous fractures distributed in different orientation, length, location of the actual fracture network. Based on study of fracture characteristics of some fractured sites in the world, the paper presented some main items concerning to the fracture properties. A methodology of re-generating a representative element volume of fractured rock mass by DEAL.II code was presented in this paper. Finally, some applications were introduced to highlight the performance as well as efficiency of this methodology.

A synthetic rock mass (SRM) model coupling discrete fracture networks (DFNs) and a discrete element grain-based model (DEM) is used to characterize the mechanical properties of moderately jointed rockmasses under confined and unconfined conditions. The scale dependency of the rockmass properties is investigated using the concept of representative element volume (REV). The numerical results are compared with the estimated values from empirical methods. It is determined that the empirical Hoek-Brown criterion correctly estimates the unconfined strength of the rockmass with non-persistent joints, while it overestimates the strength under confined conditions. An S-shaped strength envelope is obtained from the numerical results.

A detailed study is described of the post-yield behaviour of four medium-plasticity heavily overconsolidated UK stiff clays. Sub-layers of the stiff-to-hard Gault, Kimmeridge and Oxford clays were identified, sampled and tested; these, along with facies investigated in an earlier London Clay study, had broadly similar depositional histories. The intention in considering a spread of similar sediments from the Jurassic to the Eocene was to allow any strong effects of geological age, or burial depth, to be identified. A strongly fissured meso-structure was present in three of the four clays, which had a controlling influence on their effective shear strengths, considering that the representative element volume is of paramount importance in measuring the strengths of such soils. All four soils were brittle in shear and, when sheared to sufficient displacements, developed low residual shear strengths. The stiff clays were investigated further through comparisons between natural and reconstituted behaviour, using the latter to normalise the effective stress data for volume and also considering the clays' oedometer swell sensitivities. Normal compression tests, when normalised for void index, implied different degrees of ‘structure' than undrained shear tests, showing that a more elaborate micro- and meso-fabric framework is needed to capture the behaviour of highly overconsolidated and aged geomaterials. This paper focuses on describing the study sites' geotechnical profiles and the stiff clays' yielding behaviours under one-dimensional compression and in triaxial compressive shear.

For dual-pore-fracture rock mass, by considering the effect of facture weakening, a method for determining the cohesion c N and internal friction angle O N of arbitrary plane in a representative element was suggested. It was proven to be reasonable for the coordination of the anisotropy variation curves of rock mass strength obtained by this and Attewell's methods. Introducing the method for the solving of c N and O N into the elastic-plastic FEM code developed by the authors, aimed at a rectangular underground cave, three cases with different fracture states were computed. The results show that with the increasing of fracture set number, the cohesion and internal friction angle of rock mass and the plasticity zone decreased and sharply, nonlinearly grew respectively, and the magnitude and distribution of stress and displacement in the surrounding rock mass changed obviously.

Studies of strains within granular assemblies using digital image correlation have shown that as the resolution of observation becomes finer so the detail of the local variations of strains becomes more complex. The scale of this observed complexity is typically of the order of a few (5–10?) particles. The notion of a localised shear band of uniform shear or volumetric strain is not easily supported. In addition, studies reveal somewhat regular patterns of heterogeneity within samples which have been subjected to uniform external boundary deformations. A heterogeneous state is the natural state for granular materials. These observations have implications for the scales that should be adopted for testing of granular materials either in single-element or in physical model tests. Testing of a single element of a size that just accommodates a single region of ‘localisation’ will inevitably impose constraints on the particles in this region. On the other hand, one can envisage a representative element that is uniformly heterogeneous. Such an element would need to have dimensions that are large in comparison with the dimensions of the building blocks of the patterns of heterogeneity. These would define a length scale that is two orders of magnitude greater than typical particle sizes.

An elastic-plastic model was developed to describe the deformation and permeability of fractured rocks under confining pressure. Elastic and elastic-plastic contact models were used in the model to analyze the deformations of a representative element containing a single fracture under various confining pressures. The present work utilized elements from contact mechanics and viscous flows to derive an expression for permeability of fractured rocks under a range of confining pressures. The elastic-plastic model predictions for coal permeability under loading and unloading confining pressure were compared with the experimental data. The new model exhibited trends similar to the data for the range of confining pressures used in the experiments. The model can be used to predict the permeability of other fractured media with different material properties.

This paper aims to determine the strength properties of jointed rock masses by means of the homogenization method. To reflect the microstructure of jointed rock masses, a representative element volume (REV) is selected. Assuming being rigid and perfectly plastic and utilizing the Mohr-Coulomb yield criterion for rock and joints, an upper bound limit analysis method is proposed based on the homogenization theory. By using the finite element method and Goodman joint element, a nonlinear mathematical programming with equality constraints is formulated, which can be solved by a direct iterative algorithm. Numerical results show the strength of jointed rock masses behaves anisotropy with different joint directions. This method presents an effective tool for the strength analysis of jointed rock masses.

The paper discusses the intrinsic properties, the geological history, the natural structure and the mechanical behaviour of intensely fissured clays from Santa Croce di Magliano, a site located within the East-side border of the Apennine chain (southern Italy). The clays were originally deposited elsewhere and subsequently moved and largely deformed during the Apennine orogenesis, so that their structure appears severely disturbed and fissured. The applicability of a continuum-based approach to describe the mechanical behaviour of a Representative Element Volume (REV, hereafter) of the natural, fissured clay is experimentally investigated by analysing the clay specimen deformation under plane strain compression by means of False Relief Stereophotogrammetry. The results of such analysis show that, despite the intense network of pre-existing fissures, the patterns of deformation - including the eventual development of shear bands within the REV of the natural clay - are similar to those observed for unfissured clays. Triaxial tests were carried out on both natural and reconstituted clay samples and the results were compared with those recognised in the literature to be typical of unfissured clays. Based on such comparisons, the study provides a few essential elements that are useful to define a general framework for the mechanical behaviour of intensely fissured clays.