Failure mechanisms in coal: Dependence on strain rate and microstructure

Zhao, Yixin; Liu, Shimin; Zhao, Gao‐Feng; Elsworth, Derek; Jiang, Yaodong; Han, Jiayu

doi:10.1002/2014jb011198

Cited by 65 publications

(32 citation statements)

References 60 publications

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“…Zhao et al . [] performed experimental and numerical investigations of the failure behavior of brittle coal under uniaxial compression for various loading strain rates. They reported that the strength and failure mechanisms of a coal rock mass depend on the loading strain rate and also the microstructure of the material.…”

Section: Introductionmentioning

confidence: 99%

Investigation of rock fragmentation during rockfalls and rock avalanches via 3‐D discrete element analyses

et al. 2017

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This paper investigates the characteristics of dynamic rock fragmentation and its influence on the postfailure fragment trajectory. A series of numerical simulations by discrete element method (DEM) were performed for a simple rock block and slope geometry, where a particle agglomerate of prismatic shape is released along a sliding plane and subsequently collides onto a flat horizontal plane at a sharp kink point. The rock block is modeled as an assembly of bonded spherical particles with fragmentation arising from bond breakages. Bond strength and stiffness were calibrated against available experimental data. We analyzed how dynamic fragmentation occurs at impact, together with the generated fragment size distributions and consequently their runout for different slope topographies. It emerges that after impact, the vertical momentum of the granular system decreases sharply to nil, while the horizontal momentum increases suddenly and then decreases. The sudden boost of horizontal momentum can effectively facilitate the transport of fragments along the bottom floor. The rock fragmentation intensity is associated with the input energy and increases quickly with the slope angle. Gentle slopes normally lead to long spreading distance and large fragments, while steep slopes lead to high momentum boosts and impact forces, with efficient rock fragmentation and fine deposits. The fragment size decreases, while the fracture stress and fragment number both increase with the impact loading strain rate, supporting the experimental observations. The fragment size distributions can be well fitted by the Weibull's distribution function.

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Section: Introductionmentioning

confidence: 99%

Investigation of rock fragmentation during rockfalls and rock avalanches via 3‐D discrete element analyses

et al. 2017

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“…The microstructures of a rock at the grain scale are usually associated with different mineral aggregations and microdefects such as microcracks, voids, and cleavage planes [Duan and Kwok, 2016;Hallbauer et al, 1973;Kranz, 1983;Olsson and Peng, 1976]. Numerous laboratory test results indicate that the strength and deformation responses and the associated microcracking behavior of rocks are to a large extent affected by the internal microstructures [Brace et al, 1966;Eberhardt et al, 1998;Fredrich et al, 1990;Martin and Chandler, 1994;Wong, 1982a;Zhao et al, 2014].…”

Section: Introductionmentioning

confidence: 99%

Influence of grain size heterogeneity on strength and microcracking behavior of crystalline rocks

2017

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This study numerically investigates the influence of material heterogeneity on the strength and deformation behavior and the associated microcracking process of a felsic crystalline rock using a grain‐based modeling approach in two‐dimensional Particle Flow Code. By using a heterogeneity index defined in this study, the heterogeneity induced by variation of grain size distribution can be explicitly incorporated into the numerical specimen models quantitatively. Under compressive loading, the peak strength and the elastic modulus are found to increase as the numerical model gradually changes from heterogeneous to homogeneous, i.e., a decrease of heterogeneity index. Meanwhile, the number of grain boundary tensile cracks gradually decreases and the number of intragrain cracks increases at the moment of failure. However, the total number of generated microcracks seems not to be significantly influenced by heterogeneity. The orientation of grain boundary microcracks is mainly controlled by the geometry of assembled grain structure of the numerical specimen model, while the orientation of intragrain microcracks is to a large degree influenced by the confinement. In addition, the development of intragrain cracks (both tensile and shear) is much more favored in quartz than in other minerals. Under direct tensile loading, heterogeneity is found to have no significant influence on the simulated stress‐strain responses and rock strength. Only grain boundary tensile cracks are generated when the numerical models are loaded in direct tension, and the position of generated macroscopic fracture developed upon failure of the specimen is largely affected by heterogeneity.

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“…in a random and stochastically based manner. After introducing μCT, researchers can set-up numerical models 1:1 inlcuding all relevant microscopic features [30]. After μCT image processing, slices are used to visualize the distribution of various material inclusions.…”

Section: Materials and Methodsologymentioning

confidence: 99%

Numerical Approach in Recognition of Selected Features of Rock Structure from Hybrid Hydrocarbon Reservoir Samples Based on Microtomography

Kaczmarek

Zhao

Konietzky

et al. 2017

Studia Geotechnica Et Mechanica

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Abstract:The study employs numerical calculations in the characterization of reservoir sandstone samples based on high-resolution X-ray computed microtomography. The major goals were to determine porosity through pore size distribution, permeability characterization through pressure field, and structure impact on rock strength by simulation of a uniaxial compression test. Two Miocene samples were taken from well S-3, located in the eastern part of the Carpathian Foredeep. Due to the relation between sample size and image resolution, two X-ray irradiation series with two different sample sizes were performed. In the first approach, the voxel side was 27 µm and in the second it was up to 2 µm. Two samples from different depths have been studied here. Sample 1 has petrophysical features of conventional reservoir deposits, in contrast to sample 2. The approximate grain size of sample 1 is in the range 0.1-1.0 mm, whereas for sample 2 it is 0.01-0.1 mm with clear sedimentation lamination and heterogenic structure. The porosity, as determined by µCT, of sample 1 is twice (10.3%) that of sample 2 (5.3%). The equivalent diameter of a majority of pores is less than 0.027 mm and their pore size distribution is unimodal right-hand asymmetrical in the case of both samples. In relation to numerical permeability tests, the flow paths are in the few privileged directions where the pressure is uniformly decreasing. Nevertheless, there are visible connections in sample 1, as is confirmed by the homogenous distribution of particles in the pore space of the sample and demonstrated in the particle flow simulations. The estimated permeability of the first sample is approximately four times higher than that of the second one. The uniaxial compression test demonstrated the huge impact of even minimal heterogeneity of samples in terms of micropores: 4-5 times loss of strength compared to the undisturbed sample. The procedure presented shows the promising combination of microstructural analysis and numerical simulations. More specific calculations of lab tests with analysis of variable boundary conditions should be performed in the future.

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Failure mechanisms in coal: Dependence on strain rate and microstructure

Cited by 65 publications

References 60 publications

Investigation of rock fragmentation during rockfalls and rock avalanches via 3‐D discrete element analyses

Investigation of rock fragmentation during rockfalls and rock avalanches via 3‐D discrete element analyses

Influence of grain size heterogeneity on strength and microcracking behavior of crystalline rocks

Numerical Approach in Recognition of Selected Features of Rock Structure from Hybrid Hydrocarbon Reservoir Samples Based on Microtomography

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