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A series of numerical unconfined compression tests for virtual pseudo three-dimensional colluvial–deluvial soil–rock mixture (CDSRM) specimens with different areal block proportions ( BP s), sizes and slenderness ratios were conducted to study the variations of strength, deformability and failure process. Surrogate models of the specimens were generated on the basis of statistical characterization of the mesostructures extracted from the outcrop images of Baishuihe landslide site located in Three Gorges Reservoir Area of China. We find that the strength exhibits reduction for higher BP s and exhibits enhancement for lower BP s when the size increases and become asymptotic eventually. The deformability shows a monotonically increasing linear correlation with the specimen size for most BP scenarios. Simultaneously, the strength and deformability values decrease with the specimen slenderness monotonously. These findings are different from the previous assumption that the geo-mechanical behavior of bimrock is scale-independent. Comparing the observations of this study with the reported scale effect of other geotechnical materials, we conjecture that the scale effect is due to the block size and distribution. [ABSTRACT FROM AUTHOR]

Rock slope monitoring is an important aspect of better understanding the deformation behaviours and failure mechanisms of rock slopes. In this study, a multi-smartphone photogrammetric monitoring (MSM) system for rock slope hazards was proposed and developed. The system, which has nine smartphones embedded in device units, is based on structure from motion and multi-view stereo (SfM-MVS) photogrammetry. All smartphones were controlled remotely only through smartphone applications and the 4G internet. The accuracy of the system under various shooting strategies and light conditions is comprehensively evaluated in terms of both trueness and precision for two rock slopes. The distance errors of target points and the cloud-to-cloud distance were applied to assess the trueness and precision of the reconstructed slope models through the system. The results show that easy-assembly and low-cost systems have centimetre-level accuracy in the evaluation tests. The shooting strategy with a larger overlap rate tends to improve the trueness of the system, and insufficient light conditions increase the distance errors of the system. In addition, a rock slope change detection with 0.006–1.123 m3 was monitored through the MSM system. Owing to these characteristics, the MSM system has the potential to become a helpful method for rock slope reconstruction and monitoring. [ABSTRACT FROM AUTHOR]

Joint Roughness Coefficient ( JRC ) is one of the principal parameters used to calculate the shear strength and conducting aperture of discontinuities. Originally, 10 standard discontinuity profiles were commonly associated with JRC values. However, as the original profiles provided a rough estimation of joint roughness, many researchers attempted to investigate different methods of analysis to determine JRC s accurately. In the current study, we are proposing a new method for accurate JRC estimation. Firstly, we introduced a new roughness index ( λ ) using a Root Mean Square method, which considers inclination angle, amplitude of asperities and their directions. Secondly, the logistics function between λ and JRC was derived after locating the mean line, which is the line between maximum and minimum points of asperities. Finally, three formulae were developed to calculate upper-bound, suggested and lower-bound values of JRC s in relation to the variation of λ for two-dimensional discontinuity profiles. Comparison of our experimental test results with data available in the literature showed that the proposed roughness index, λ , can be used to determine JRC values accurately resulting in better estimation of discontinuity shear strength and conducting apertures. In addition, the sensitivity of JRC , shear strength and the ratio of mechanical aperture to conducting aperture ( E / e ) with respect to λ were also investigated. The results revealed that trends of JRC , shear strength and E / e ratios are similar. These parameters are found to be most sensitive when λ is in the range of 0.05–0.20. [ABSTRACT FROM AUTHOR]

A general discrete element method-based model is proposed to investigate the cyclic freezing-thawing induced damage of fractured rocks. A set of cracks is defined as an assembly of interparticle pores that are interconnected due to self-definition (pre-existing) or contact breaking (external force induced). During the freezing-thawing simulation, only the rock grains surrounding the cracks are subjected to frost heave pressure, which are expected to cause contact breaking and crack propagation. In this sense, most of the pores that do not form cracks in the numerical model will not participate in the calculation, so the computational cost and time are substantially reduced. The cracks connected to the atmosphere, i.e. the model boundaries, are classified as inactive cracks and their frost heave pressures are removed accordingly. Therefore, model convergence is recognized when all cracks are converted to inactive. Parametric analysis is further performed to show the influence of some important input parameters, including the unfrozen water content, calibration factor of frost heave pressure, crack density and dip. Finally, the freezing-thawing damage of rocks is quantified by the reduction in uniaxial compressive strength after a prescribed number of freezing-thawing cycles. The results are validated with an analytical solution. It is shown that the rock strength degradation, crack evolution, heave and settlement can be well simulated by the proposed model. This methodology can be extended to large-scale problems such as glacier slope instability or landslides. [ABSTRACT FROM AUTHOR]

In this study, to investigate the variability of mechanical parameters of rock, a three-dimensional (3D) discrete element model (DEM) with the consideration of random microcracks was proposed. The random microcracks follow the negative power-law distribution with upper and lower limits of microcrack size. The results showed that coefficient of variations (COVs) and average values of elastic modulus, Poisson's ratio, unconfined compression strength and tensile strength of Lac du Bonnet granite are well matched through the present model. The present simulations indicate that the large COVs were induced by the interconnected large microcracks. The parametric study clearly indicates that the random microcracks significantly affect COVs, while the effect of grain size variation can be ignored. The size of microcracks determines the variability of mechanical parameters, and the volume density of microcracks can significantly influence the COVs. The correlation between the fractal dimension of microcrack size distribution and COVs is not linear. The increasing variability of microcrack density can result in the increase of COVs. Finally, a calibration procedure was proposed to determine the present model's parameters. [ABSTRACT FROM AUTHOR]

Flexural toppling is one of the main failure modes of natural and manmade anti-dip layered rock slopes. Based on cantilever slab tensile theory, the failure mechanism of flexural toppling was analyzed. A toppling slope is divided into three parts: the stability, tensile and shear zones. By considering this failure mechanism, a new stability analysis method for slopes against flexural toppling failure is proposed using equilibrium theory. In addition, a sensitivity analysis is performed to investigate the locations of possible failure surfaces and zones as well as changes in the stability of anti-dip rock slopes under different conditions. The results show that the positions of the inter-column forces have almost no effect on the stability factor but affect the areas of the tensile zone and the shear zone. The angle of the most dangerous potential failure surface increases with increasing dip angle and slope height, whereas the stability factor is negatively correlated with the dip angle and slope height but is positively correlated with the layer thickness. The failure mode is essentially flexural toppling when the layer thickness is small, but the failure mode gradually transitions to shear-sliding with increasing layer thickness. Finally, a real case study is analyzed using this method, and the calculated results are consistent with the actual conditions. [ABSTRACT FROM AUTHOR]