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Nonlinear criterion for strength mobilization in Brittle failure of rock and its extension to the tunnel scale

International Journal of Mining Science and Technology 2022年第4期32卷 685-705页

作者： Rodolfo Cabezas Javier Vallejos Faculty of Engineering and Technology Universidad San SebastianSantiagoChile Advanced Mining Technology Center Universidad de ChileSantiagoChile Department of Mining Engineering Universidad de ChileSantiagoChile

As underground excavations are getting deeper and field stresses increase, the behavior of intact rock blocks plays an increasingly important role in understanding and estimating the overall rock mass strength. To model the brittle behavior of intact rock blocks, the stress–strain curve is usually idealized considering a linear strength mobilization approach(cohesion-weakening-friction-strengthening, CWFS),however, it is well recognized that rock presents a nonlinear behavior in terms of the confining stress.This study extends the strength mobilization in Brittle failure of rock using nonlinear criteria. To determine the model parameters, a standard statistical method that uses the complete laboratory stress–strain curves of the intact rock is employed. Several hypotheses of linear and nonlinear models are statistically compared for different types of rock and confining stress levels. Results demonstrate that the best approach to model the Brittle failure of rock is to consider a nonlinear strength envelope, such as the Hoek-Brown criterion assuming a residual uniaxial compressive strength different from zero and a mi parameter that increases, both with simultaneous mobilization. This model helps to recreate highconfining conditions and a more realistic transition between peak and post-peak strength. The obtained parameters are discussed and compared with literature values to verify the validity and to develop guidelines for the estimation of parameters, providing an objective mobilization criterion. Finally, the nonlinear model was applied to a finite element code and extended to a tunnel scale in the brittle rock under high-stress conditions. A reasonable fit between the simulations and the in-situ overbreak measurements was found.

关键词： Nonlinear strength Strength mobilization Brittle failure Intact rock Scaling

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Dynamic behaviors of rockslides subjected to Brittle failure of locked segments

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Journal of Mountain Science 2023年第2期20卷 532-541页

作者： HU Kai ZHAO Xiao-yan ZHANG Guang-ze Faculty of Geosciences and Environmental Engineering Southwest Jiaotong UniversityChengdu 611756China China Railway Eryuan Engineering Group Co. LtdChengdu 610031China

Locked segments are recognized as a critical role that controls the stability of rock slopes but remain an unclear and challenging problem with respect to their role incorporated into the failure mechanism.In order to study the effect of the locked segments on the initial failure process of rockslides,thirty-six groups of locked segment specimens with three different lithologies were prepared,direct shear tests were carried out to obtain the accelerations caused by Brittle failure of the locked segment specimens.Experiment results showed that the maximum accelerations caused by the Brittle failure of locked segment specimens was 2.91 g in the horizontal direction,and 3.18 g in the vertical direction.We took the Wangjiayan rockslide in 2008 Wenchuan earthquake as an example,the critical balance condition of the sliding mass under combined effect of gravity and accelerations induced by Brittle failure of locked segment was analyzed,which indicated that the initial failure process of the Wangjiayan rockslides was notably influenced by the existence of the locked segment.The departure acceleration and direction of the Wangjiayan rockslide were proposed.The study results can provide a new insight into the understanding of the initial failure mechanism of rockslides with locked segments.

关键词： Rockslides Rockfalls Locked segment Direct shear test Initial failure mechanism Sudden departure Brittle failure

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Pseudo-discontinuum model to simulate hard-rock mine pillars

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Underground Space 2023年第4期11卷 81-95页

作者： Erick Ro genes Alessandra dos Santos Gomes Marcio Muniz de Farias Leandro Lima Rasmussen Faculty of Technology University of BrasiliaDF 70910-900BrasiliaBrazil

In this study,the pseudo-discontinuum modeling technique,called continuum Voronoi block model(CVBM),was applied to repre-sent the behavior of hard-rock pillars from underground mines subjected to high field stresses.The CVBM’s ability to produce numerical results consistent with the observed behavior of pillars is demonstrated through the numerical analysis of a hypothetical case and a back analysis of the Creighton mine pillar.The results show that the model can capture convergence displacements and explicitly show the formation of macro-fractures parallel to excavation walls,intact rock slabs,and V-shaped notches.These components are characteristics of Brittle failure induced by highly stressed ground conditions.The studies presented in this work confirm the CVBM as a convenient tool for the numerical modeling of intact rock pillars excavated in deep underground mines.

关键词： Brittle failure Spalling Bulking Voronoi tessellation

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Analysis of the stress ratio of anisotropic rocks in uniaxial tests

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International Journal of Mining Science and Technology 2017年第3期27卷 531-535页

作者： Wang Miaomiao Li Pei Wu Xiaowa Xu Dan Key Laboratory of Shale Gas and Geoengineering Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China Institute of Geomechanics Chinese Academy of Geological Sciences Beijing 100081 China

The effect of structural discontinuities on the progressive failure process of anisotropic rocks should be paid particular attention.The crack damage stress σ_(cd),also considered as the yield strength,and the relationship between σ_(cd) and the uniaxial peak strength σ_(ucs) of anisotropic rocks for different orientations 8 of the isotropy planes with respect to the loading directions were investigated theoretically and experimentally.A theoretical relation of σ_(cd)/σ_(ucs) with the function of the shape parameter m was established.Additionally,uniaxial compression tests of shale samples were conducted for several inclinations θ.The test result of σ_(cd)/σ_(ucs) was close to the theoretical value for a given orientation.Furthermore,both experimental results and theoretical solutions of σ_(cd)/σ_(ucs) were independent of the inclination θ while σ_(cd) andσ_(ucs) were strongly affected by θ.The strength ratio σ_(cd)/σ_(ucs) may therefore be an intrinsic property of anisotropic rocks and could be used to predict the failure of rock samples.

关键词： Anisotropic rocks Uniaxial compression test Brittle failure Crack damage stress Stress ratio

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Effects of spatial variation in cohesion over the concrete-rock interface on dam sliding stability

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Journal of Rock Mechanics and Geotechnical Engineering 2015年第6期7卷 659-667页

作者： Alexandra Krounis Fredrik Johansson Stefan Larsson Division of Soil and Rock Mechanics KTH Royal Institute of Technology

The limit equilibrium method （LEM） is widely used for sliding stability evaluation of concrete gravitydams. failure is then commonly assumed to occur along the entire sliding surface simultaneously.However, the brittle behaviour of bonded concrete-rock contacts, in combination with the varying stressover the interface, implies that the failure of bonded dam-foundation interfaces occurs progressively. Inaddition, the spatial variation in cohesion may introduce weak spots where failure can be initiated.Nonetheless, the combined effect of Brittle failure and spatial variation in cohesion on the overall shearstrength of the interface has not been studied previously. In this paper, numerical analyses are used toinvestigate the effect of Brittle failure in combination with spatial variation in cohesion that is taken intoaccount by random fields with different correlation lengths. The study concludes that a possible existenceof weak spots along the interface has to be considered since it significantly reduces the overallshear strength of the interface, and implications for doing so are discussed.

关键词： Concrete gravity dam Sliding stability Cohesion Brittle failure Spatial variation

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Italy Tower Collapse in São Josédo Rio Preto-S.Paulo,Brazil

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Journal of Civil Engineering and Architecture 2022年第5期16卷 270-276页

作者： Fernando Stucchi Polytechnic School USPSão PauloBrazil

This paper discusses the collapse of Italy Tower,a 16-storeybuilding,that occurred 10 years after construction,with 10 floors tumbling upside down into a side street.The designed structure and the structure as built w... 详细信息

关键词： High-rise buildings columns transition piles collapse Brittle failure

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Considerations of rock dilation on modeling failure and deformation of hard rocks-a case study of the mine-by test tunnel in Canada

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Journal of Rock Mechanics and Geotechnical Engineering 2010年第4期2卷 338-349页

作者： Xingguang Zhao Meifeng Cai MCai Beijing Research Institute of Uranium Geology Beijing100029China School of Civil and Environmental Engineering University of Science and Technology BeijingBeijing100083China School of Engineering Laurentian UniversitySudburyP3E 2C6Canada

For the compressive stress-induced failure of tunnels at depth, rock fracturing process is often closely associated with the generation of surface parallel fractures in the initial stage, and shear failure is likely to occur in the final process during the formation of shear bands, breakouts or V-shaped notches close to the excavation boundaries. However, the perfectly elastoplastic, strain-softening and elasto-brittle-plastic models cannot reasonably describe the Brittle failure of hard rock tunnels under high in-situ stress conditions. These approaches often underestimate the depth of failure and overestimate the lateral extent of failure near the excavation. Based on a practical case of the mine-by test tunnel at an underground research laboratory (URL) in Canada, the influence of rock mass dilation on the depth and extent of failure and deformation is investigated using a calibrated cohesion weakening and frictional strengthening (CWFS) model. It can be found that, when modeling Brittle failure of rock masses, the calibrated CWFS model with a constant dilation angle can capture the depth and extent of stress-induced Brittle failure in hard rocks at a low confinement if the stress path is correctly represented, as demonstrated by the failure shape observed in the tunnel. However, using a constant dilation angle cannot simulate the nonlinear deformation behavior near the excavation boundary accurately because the dependence of rock mass dilation on confinement and plastic shear strain is not considered. It is illustrated from the numerical simulations that the proposed plastic shear strain and confinement-dependent dilation angle model in combination with the calibrated CWFS model implemented in FLAC can reasonably reveal both rock mass failure and displacement distribution in vicinity of the excavation simultaneously. The simulation results are in good agreement with the field observations and displacement measurement data.

关键词： hard rocks Brittle failure deformation dilation angle model confinement plastic shear strain mine-by test tunnel

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