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The representative elementary volume (REV) is the premise of the continuous-media method of analysis, and the investigation of the REVs of fractured rock masses is a fundamental area of rock mechanics research. The existence of an REV can be determined based on a variety of physical parameters. This paper presents an analysis of the REV from the view of blockiness, which is defined as the percentage of the volume of isolated blocks formed by fractures in the total rock volume. Seventy-seven types of fractured rock mass models were developed based on 7 classes of fracture persistence and 11 classes of spacing that are suggested by the International Society for Rock Mechanics (ISRM) fracture classification. Rock blocks in each of the 77 types of fractured rock mass models were identified using GeneralBlock to determine the variation in blockiness with model domain sizes, which were changed from 2 to 20 times the fracture spacing. For each model domain size 9 random realizations were carried out to reduce the effects of randomness. The coefficient of variation (C v ) was then used to quantify the variability of the 9 random realizations. The fluctuation in blockiness with the variation in the scale of the model region was also investigated. In this way, the size of the REV in these models can be calculated using the average and the variance of the blockiness as indicators of the convergence. The blockiness of these fractured rock masses can be determined at the REV volume. The results indicate that of the 77 models, 76 REV sizes are between 2 and 20 times the fracture spacing. The fractured rock mass with a wide fracture spacing and very high persistence (WS2–VHP) has a REV size that exceeds 20 times the fracture spacing. Thus, the WS2–VHP model should be investigated further to validate this concept. [ABSTRACT FROM AUTHOR]

Identifying blocks formed by various fractures is important in rock engineering. Most studies focus mainly on blocks formed by planar fractures whereas curved fractures are rarely considered. However, large fractures observed in the field are often curved. This paper presents a new method for identifying rock blocks formed by both curved and planar fractures based on the element-block-assembling approach, in which the study domain is divided into numerous tetrahedral subdomains under the constraint of curved fractures and the subdomains are further decomposed into element blocks by extended planar fractures. When the fractures are restored to finite dimensions, the element blocks are combined and the subdomains are assembled to form complex blocks. The combination of the two subdomains is skipped if and only if their common facet lies on a curved fracture. A computer program was implemented based on the method introduced in this study and the verification examples indicated that this method could effectively handle both convex and concave blocks. [ABSTRACT FROM AUTHOR]

The large-scale construction of railway tunnels in China is hindered by several challenges, including large depths, large tunnel cross-sections, and fragile geological conditions. In this paper, we explored a new physical and numerical simulation method that improves upon the currently used methods to investigate the deformation and failure modes of weak rocks surrounding a tunnel. We also compared the results from physical tests and numerical simulations with the field measurements to demonstrate the effectiveness of the proposed numerical simulation method. In the physical model test, an artificial speckle field was developed by staining quartz sand particles and mixing the particles with barite powder and petroleum jelly in preset proportions. The artificial speckle field was employed in the digital speckle correlation method (DSCM) to monitor the evolution of the strain field on the surface of the plain strain model for tunneling during loading. A secondary strain-softening constitutive model using the numerical modeling code FLAC3D was developed (degradation constitutive model) by considering the deformation modulus degradation in the numerical simulation. The failure mode of weak rocks surrounding a tunnel in the physical model test was examined using the developed degradation constitutive model. Both the physical and numerical results revealed that the least stable area was the shear wedge along the minimum principal stress, which was confirmed in the damage zone of the surrounding rocks. The results were consistent with previous research findings. The results of the DSCM in the physical model test indicated that the shear wedge in the middle part of the tunnel and the cracks around the arch of the tunnel were induced by shear strain, whereas the collapse of the arch was attributed to a combination of tensile strain and shear strain. A comparison of the physical and numerical simulation results demonstrated that the degradation constitutive model can be used to describe the extent and depth of the excavation damage zone of tunneling. A comparison of the displacements from the numerical simulation and field measurements indicated that the degradation model can be used to capture the displacement of weak rocks surrounding tunnels. [ABSTRACT FROM AUTHOR]