Evolution and effect of the stress concentration and rock failure in the deep multi-seam coal mining
题名：深部多煤层开采中应力集中与岩石破裂的演变与影响
Environmental Earth Sciences, August 2014, Volume 72, Issue 3, pp 629-643
Abstract: Supports crushing accident occasionally occurs in the protected seam exploitation of deep multi-seam coal mining structure and results in adverse effect to the production. To prevent its recurrence in a newly developed working field, a 3D numerical extraction model was built based on the geologic and mining conditions of Jining coal mine to evolve the changes, state and characteristics of the reconstructed vertical and lateral stress in rock interlayer after protective seam exploitation. Stress release and increase zones of this mining structure were separated. Mining-induced localized stress concentration and the interlayer rock failure behavior were explored. The action of concentrated stress on the hydraulic supports in protected seam was discussed upon the major stress redistribution. Using the infinitesimal strain method, a mechanical model was created to further explore, from the vertical and lateral directions, the cause and mechanism of localized stress concentration and rock failure behavior in rock interlayer. The field investigation was finally performed to verify the numerical and mechanical results, and the essential control measures were proposed to prevent this accident. Key findings of this study bring some new insights into the deep multi-seam coal extraction and help to promote a more reliable underground mining.
Influence of Coal Extraction Operation on Shaft Lining Stability in Eastern Chinese Coal Mines
题名：中国华东煤矿回采运作对井筒支护稳定性的影响
Geotechnical and Geological Engineering, August 2014, Volume 32, Issue 4, pp 821-827
Abstract: In order to find the relationship between the shaft lining stability and the coal extraction operation, a 3D numerical model of strata layers and shaft lining was established for simulating the influence of coal extraction operation on shaft lining. Certain factors including mining depth, safety pillar width, mining width and mining height were taken as the influence factors in the simulation. The results indicated that the coal extraction could lead to the initiation of the failure in the aquifer and rock layers. As the mining depth increases, the shear strain increment in aquifer becomes small. In this case, the distance between mining panel and aquifer should be larger than 220 m and the safety pillar width should not <70 m. The maximum principal stress in aquifer had a little relation to mining operations. The mining panel width should not exceed 50 m without any support.
Experimental and numerical analysis of the time-dependent behaviour of argillaceous red sandstone under high in situ stress
题名：高现场应力下粘土红砂石时间依赖特征的实验与数值分析
Bulletin of Engineering Geology and the Environment, July 2014
Abstract: Understanding the time-dependent behaviour of soft rock under high in situ stress is essential to the evaluation of the long-term stability of the deep-buried tunnels in expressways or coal mines. This paper presents an experimental and numerical study of the time-dependent behaviour of argillaceous red sandstone under high in situ stress. First, several triaxial creep tests for strongly and moderately weathered specimens under the confining pressure of 20–40 MPa were conducted, and the variation of time-dependent damage with time was obtained by investigating the evolution of volumetric strain during the creep process. The test results verify that creep damage has a similar effect on both axial strain and lateral strain of argillaceous red sandstone. Second, a creep damage model that is able to describe nonlinear variation in creep strain and volume expansion for sandstone under high in situ stress was established. Last, the parameters of the proposed model were determined by a back analysis method. The results of back analysis show that the model is able to describe the nonlinear variation in creep strain and volume expansion during the creep process very well.
Shear behavior of waste rock materials in drained and undrained ring shear tests
题名：排水与不排水环剪测试中废石料的剪切特性
Geosciences Journal, July 2014
Abstract: The denudation processes in abandoned mines pose environmental and social problems. Insufficient remediation and cleanup modify the physicochemical properties near the mine sites. In addition, large amounts of sediment and debris can flow downward due to heavy rainfall. Here, the shear characteristics of mine deposits are presented rather than their chemical contaminants, which include heavy metals. Drained and undrained ring shear tests were performed on waste rock materials that were collected from pyrophyllite mine deposits in the mountainous region of Korea. These samples were classified as gravelly sandy soils (i.e., with an effective grain size of D10 = 0.3 mm and a uniformity coefficient of cu = 5). The following three tests were performed: (i) shear stress measurement with shearing time for a given shear velocity (i.e., 0.1 mm/sec), (ii) shear stress as a function of shear velocity, and (iii) shear stress as a function of normal stress. The fully saturated samples were subjected to different normal stresses (i.e., 25 and 100 kPa) and shear velocities (i.e., 0.01, 0.1, 1, and 100 mm/sec). The waste materials exhibited a strain-softening behavior regardless of the drainage and shear velocity condition. In addition, the shear stress was strongly influenced by the shear velocity and increased with increasing shear velocity and normal stress in the post-failure stage. Using grain size distribution analyses, we show that significant grain crushing occurs in the shear zone during shearing. Under relatively high shear velocity conditions (i.e., >;100 mm/sec), the grain crushing effect is more significant and results in rapid mass movements.
A Study on Crack Damage Stress Thresholds of Different Rock Types Based on Uniaxial Compression Tests
题名：基于单轴压缩测试的不同岩石裂纹损伤应力临界值研究
Rock Mechanics and Rock Engineering,July 2014, Volume 47, Issue 4, pp 1183-1195
Abstract: When rock samples are loaded until macroscopic fractures develop, the failure process can be divided into several stages based on axial and lateral strain responses or the acoustic emission sequence during uniaxial compression tests. Several stress thresholds may be identified: the crack closure stress σ cc, crack initiation stress σ ci, crack damage stress σ cd, and uniaxial compressive strength σ ucs; these may be used as a warning indicator for rock rupture. We investigated the crack damage stress σ cd, its threshold, and a possible relationship between σ cd and the uniaxial compressive strength. The σ cd of different rock types were compiled from previous studies based on uniaxial compression tests. The results showed that the overall averages and standard deviations of σ cd /σ ucs for igneous, metamorphic, and sedimentary rocks were ~0.78 (±0.11), ~0.85 (±0.11), and ~0.73 (±0.18), respectively. There were no significant differences in σ cd /σ ucs between the different rock types, except that the sedimentary rock had a slightly larger standard deviation attributed to the variation of porosity in the samples, while the metamorphic rock had higher average σ cd /σ ucs resulting from the small statistical sample size. By excluding the higher-porosity (>10 %) rock samples, the averages and standard deviations of σ cd /σ ucs for igneous, metamorphic, and sedimentary rocks were ~0.78 (±0.09), ~0.85 (±0.09), and ~0.78 (±0.11), respectively. The results imply that the rock origin process (i.e., igneous, metamorphic, and sedimentary) has a minimal effect on σ cd /σ ucs. The ratio σ cd/σ ucs could be an essential intrinsic property for low-porosity rocks, which could be used in rock engineering for predicting the failure process.
ISRM Suggested Method for Determining the Abrasivity of Rock by the CERCHAR Abrasivity Test
题名：国际岩石力学学会建议方法：通过CERCHAR研磨测试确定岩石研磨性
Introduction: Rock abrasivity plays an important role in characterizing a rock material for excavation purposes. Abrasion can be defined as the wearing or tearing away of particles from the surface, i.e. it is a process causing removal or displacement of material at a solid surface, which will lead to wear, especially on tools that are used in mining, drilling, and tunneling applications. The CERCHAR Abrasivity Test is a method to determine an index called CERCHAR Abrasivity Index (CAI) for the rock’s abrasivity.
The test was originally developed by the Laboratoire du Centre d’Études et Recherches des Charbonnages (CERCHAR) de France for coal mining applications (Cerchar 1986). Two standards exist for this test method: the French standard AFNOR NF P 94-430-1 (2000) and ASTM D7625-10 (2010). The test is widely used in research and practice. There are essentially two designs of testing apparatus: the original design as developed at the CERCHAR Centre (Valantin 1973) and a modified design as....
Mechanical behavior of typical hazardous waste and its influence on landfill stability during operation
题名：典型危险废物的力学特性以及其对填埋场稳定性的影响
Journal of Material Cycles and Waste Management, October 2014, Volume 16, Issue 4, pp 597-607
Abstract: The stability of hazardous waste (HW) landfill is a major security risk to the landfill environmental safety. The mechanical behavior of waste controls many aspects of landfill design and operation, including stability and settlement issues and the integrity of geosynthetic and liner components. This study presents the results of a laboratory experiment to learn the mechanical properties of HW collected from the Hangzhou HW landfill. Measured mechanical behavior was compared with results for municipal solid waste (MSW) to assess their discrepancies. The particle size of HW was analyzed by the sieving and hydrometer methods. Because HW comes primarily from industrial plants in the form of sludge or slag, their particle sizes are generally smaller than those of MSW. This study indicates that the shear strength parameters of HW are more sensitive to the methods of testing and calculation than those of MSW. Numerical simulations demonstrate that the safety factor of a landfill is affected by the mechanical properties of HW, especially cohesion and friction angle. Because of the lower particle size and wider compression ratio, compared to MSW, an HW landfill should be taken more care in its operational procedures so as to increase its stability.
Numerical Simulation of Squeezing Failure in a Coal Mine Roadway due to Mining-Induced Stresses
题名：开采应力引起的煤矿巷道挤压破坏数值模拟
Rock Mechanics and Rock Engineering, September 2014
Abstract: Squeezing failure is a common failure mechanism experienced in underground coal mine roadways due mainly to mining-induced stresses, which are much higher than the strength of rock mass surrounding an entry. In this study, numerical simulation was carried out to investigate the mechanisms of roadway squeezing using a novel UDEC Trigon approach. A numerical roadway model was created based on a case study at the Zhangcun coal mine in China. Coal extraction using the longwall mining method was simulated in the model with calculation of the mining-induced stresses. The process of roadway squeezing under severe mining-induced stresses was realistically captured in the model. Deformation phenomena observed in field, including roof sag, wall convexity and failed rock bolts are realistically produced in the UDEC Trigon model.
Dilation and Post-peak Behaviour Inputs for Practical Engineering Analysis
题名：剪胀与后峰值特征输入在实际工程分析中的应用
Geotechnical and Geological Engineering, September 2014
Abstract: Numerical models used by engineers to simulate rockmass behaviour are often limited by poor or incomplete representations of post-yield behaviour. Although conventional plasticity theory is often capable of predicting stress distributions around excavations, it is more difficult to fully capture the complex displacement patterns that are observed in situ. This is largely because conventional material models fail to capture the confinement and damage accumulation dependencies of post-yield dilatancy. Even with these mechanistic limitations in mind, simple constitutive models can be used for practical applications, although no reliable methodology for parameter selection exists. This study aims to remedy this deficiency. In this work, existing models for dilatancy based on laboratory testing data are considered and their limitations are discussed. The most accurate of these models add complexity to the analyses and also require additional input parameters beyond those which are typically obtained from laboratory testing. While the concept of a constant dilation angle during yield is not physically valid, it may be, in some cases, a sufficient model for ground response prediction. It is of interest, for practical engineering analyses, to understand the conditions where this additional complexity is required and where simplified models may be adequate. For the case of circular excavations in a uniform stress field, plastic zone displacements for mobilized and constant dilation angle models are compared and parametric sensitivities are discussed. Many material parameter combinations representative of relatively ductile rockmasses are tested, and it is shown that for most of these cases, the results obtained using a mobilized dilation angle can be well approximated through the use of an appropriate best-fit constant dilation angle. Through a statistical analysis of the data, a practical methodology for the selection of a constant dilation angle for use in simpler continuum numerical models is proposed. Further analysis under more general conditions performed using finite-difference models shows that the methodology can be applied to non-circular excavation geometries (errors are only significant near corners), general strain softening behaviour, and non-hydrostatic stress conditions where the stress anisotropy is moderate. An example of the methodology is presented in the context of extensometer data from a deep mine shaft, and the success of the methodology in providing a reasonable dilation angle estimate is demonstrated.
Microseismic and acoustic emission effect on gas outburst hazard triggered by shock wave: a case study
题名：微震与声发射对冲击波引发瓦斯突出灾害的影响：工程实例研究
Natural Hazards, September 2014, Volume 73, Issue 3, pp 1715-1731
Abstract: It has a significant and practical meaning for warning precisely gas outburst to reveal microseismic (MS) and acoustic emission (AE) effect of gas outburst precursor. It was thoroughly investigated and discussed on MS and AE effect on an abnormal gas outburst triggered by a strong rockburst using MS- and AE-monitoring systems through spectral analysis technique. We obtained main conclusions are as: (1) MS amplitude prominently decreased prior to outburst, the spectrum significantly moved from extremely low-frequency to high-frequency band, and evolved from “single-peak type” (the center frequency was about 1.5–3.5 Hz) to “multi-peak type” (the peak frequencies were about 25, 50, 75 and 125 Hz, respectively). (2) During the initiative stage of outburst, MS spectrum manifested the broadband distribution, and the predominant frequency was about 20–35 Hz. The high-frequency portion was generated by micro-cracks, and the low-frequency part attributed to macro-fracture for gas outburst channel. (3) The rockburst stimulated micro-fissures formation for gas emission channels, and maintained the event count of MS and AE signals in a relatively higher level, which is a major discrepancy to the common belief that both the total energy and event count should simultaneously and suddenly reduce to the lowest value in a non-outburst coal seam.
Lattice-Boltzmann simulation of microscale CH4 flow in porous rock subject to force-induced deformation
题名：力致变形多孔岩石中微尺度甲烷流动的格子Boltzmann模拟
Chinese Science Bulletin, September 2014, Volume 59, Issue 26, pp 3292-3303
Abstract: Accurate knowledge of the influence of rock deformation on the permeability of fluid flow is of great significance to a variety of engineering applications, such as simultaneous extraction of coal and gas, oil/gas exploitation, CO2 geological sequestration, and underground water conservation. Based on the CT representation of pore structures of sandstones, a LBM (Lattice Boltzmann Method) for simulating CH4 flow in pore spaces at microscale levels and a parallel LBM algorithm for large-size porous models are developed in this paper. The properties of CH4 flow in porous sandstones and the effects of pore structure are investigated using LBM. The simulation is validated by comparing the results with the measured data. In addition, we incorporate LBM and FEM to probe the deformation of microstructures due to applied triaxial forces and its influence on the properties of CH4 flow. It is shown that the proposed method is capable of visually and quantitatively describing the characteristics of microstructure, spatial distribution of flow velocity of CH4, permeability, and the influences of deformation of pore spaces on these quantities as well. It is shown that there is a good consistency between LBM simulation and experimental measurement in terms of the permeability of sandstone with various porosities.
Quasi-static and dynamic fracture behaviour of rock materials: phenomena and mechanisms
题名：岩石材料的准静态与动态断裂特性：现象与机理
International Journal of Fracture, September 2014, Volume 189, Issue 1, pp 1-32
Abstract: An experimental investigation is conducted to study the quasi-static and dynamic fracture behaviour of sedimentary, igneous and metamorphic rocks. The notched semi-circular bending method has been employed to determine fracture parameters over a wide range of loading rates using both a servo-hydraulic machine and a split Hopkinson pressure bar. The time to fracture, crack speed and velocity of the flying fragment are measured by strain gauges, crack propagation gauge and high-speed photography on the macroscopic level. Dynamic crack initiation toughness is determined from the dynamic stress intensity factor at the time to fracture, and dynamic crack growth toughness is derived by the dynamic fracture energy at a specific crack speed. Systematic fractographic studies on fracture surface are carried out to examine the micromechanisms of fracture. This study reveals clearly that: (1) the crack initiation and growth toughness increase with increasing loading rate and crack speed; (2) the kinetic energy of the flying fragments increases with increasing striking speed; (3) the dynamic fracture energy increases rapidly with the increase of crack speed, and a semi-empirical rate-dependent model is proposed; and (4) the characteristics of fracture surface imply that the failure mechanisms depend on loading rate and rock microstructure.
Observation and Numerical Analysis of the Scope of Fractured Zones Around Gateroads Under Longwall Influence
题名：长臂开采影响下巷道破坏区域范围研究与数值模拟
Rock Mechanics and Rock Engineering, September 2014, Volume 47, Issue 5, pp 1939-1950
Introduction：There exists a trend in China that high productivity longwall face which produces 8.0–10.0 million tons of raw coal per annum is widely employed. The stability of the gateroads during the life of longwall mining is the main concern of the success of high-production longwall face. After a gateroad is driven into rock strata, the primary equilibrium state is disturbed and, as a result, the surrounding rocks are unavoidably broken or fractured (Dong et al. 1994). The extent of the fractured zones mainly depends on: stress characteristics where the gateroad is located; physical, mechanical and rheological properties of rocks; tectonic structure of the rock mass; and an applied extraction and support system (Cai 2008; Chu et al. 2007; Coggan et al. 2012; Feng et al. 2012; Wang et al. 2000). In the case of longwall gateroads, the SFZ can rapidly develop with the influence of longwall mining (Esterhuizen and Barczak 2006; Hao et al. 2004; Walentek et al. 2009). Accurately evaluation....
Mechanical and Elastic Properties of Transversely Isotropic Slate
题名：横向同性岩石的力学与弹性性能
Rock Mechanics and Rock Engineering, September 2014, Volume 47, Issue 5, pp 1763-1773
Abstract: Planes of weakness like schistosity and foliation affect the strength and deformational behaviors of rocks. In this paper, an attempt has been made to study the elastic and strength behavior of slate rocks obtained from foundation of Sardasht dam site in Iran. Wet and dry specimens with different orientation of foliation were evaluated under uniaxial, triaxial, and Brazilian tests. According to the results obtained, slate mechanically pronounced U-shaped anisotropy in uniaxial and triaxial compression tests. In addition, the degree of anisotropy for the slates tested in current study was relatively high, showing the effect of foliation plane on strength and elastic parameters. It was concluded that stiffness of the samples decrease as the angle of anisotropy reaches 30–40°. This change was more pronounced for wet comparing to dry samples. However, the tensile strength obtained during Brazilian tests indicated that there is no apparent relationship between angle of anisotropy and tensile strength. However, increasing the water saturation decreased the tensile strength of the samples. The calculated elastic moduli referring to different anisotropy angles could be valuable for the design of various engineering structures in planar textured rock masses.
Case Studies of Rock Reinforcement Components and Systems Testing
题名：岩石加固组件与系统测试实例研究
Rock Mechanics and Rock Engineering, September 2014, Volume 47, Issue 5, pp 1589-1602
Abstract: Rock reinforcement is widely used in tunnels and surface and underground mines. A large number of proprietary products are available in various configurations of components. While the mechanical properties of the primary element are available from product brochures, the associated component properties may vary widely and adversely influence the overall performance of the system. Field pull out tests are most commonly used to measure the system response in the toe anchor region. However, the response of the collar region is less commonly considered but may be more important. Several case studies are described in which various components and systems of rock bolts and cable bolts have been subjected to static loading in the laboratory and in the field. The results generally demonstrate the importance of considering the properties of all the components and not simply those of the primary element. In some cases, the internal fixtures have strengths much less than the elements. Often it has also been found that the fixture at the collar has significantly less strength than the element and this will result in complete loss of function in restraining surface support hardware, such as plates, mesh and reinforced shotcrete.
Evaluation of Fragments from Disc Cutting of Dry and Saturated Sandstone
题名：干燥与饱水砂岩的盘形滚刀切片研究
Rock Mechanics and Rock Engineering, September 2014, Volume 47, Issue 5, pp 1891-1903
Abstract: As the use of mechanical excavation in tunneling and mining activities expands, so has the use of disc cutters in various ground conditions. The impact of moisture content on rock behavior and rock excavation by disc cutters is examined in this study. This was done through a series of full-scale cutting tests using a 292 mm (11.5 in.) disc cutter in a moderate strength sandstone. The muck from the cutting tests was used to determine coarseness index (CI) and absolute size constant (x′). x′ was calculated using Rosin–Rammler distribution (or Weibull) curve, a statistical technique to look at the fragmented rock products. This approach is very popular among the mineral-processing professionals for the evaluation of the particle sizes of the comminution products. x′ and CI show a reasonable correlation with the specific energy of cutting and production rate. Both of these indicators were found to be dependent on the cut spacing and the interaction between the adjacent cuts, as anticipated. This paper explains the background information on this topic, reviews the laboratory testing, and offers analysis of the results of grain size distribution and its relationship with specific energy and cutting geometry. It should be noted that the experimental program was limited to only one rock type and additional testing on the other rock types is required to expand the results of the current study.
The influence of porosity and vesicle size on the brittle strength of volcanic rocks and magma
题名：孔隙度和囊泡大小对火山岩与岩浆脆裂强度的影响
Bulletin of Volcanology, August 2014, 76:856
Abstract: Volcanic rocks and magma display a wide range of porosity and vesicle size, a result of their complex genesis. While the role of porosity is known to exert a fundamental control on strength in the brittle field, less is known as to the influence of vesicle size. To help resolve this issue, here, we lean on a combination of micromechanical (Sammis and Ashby's pore-emanating crack model) and stochastic (rock failure and process analysis code) modelling. The models show, for a homogenous vesicle size, that an increase in porosity (in the form of circular vesicles, from 0 to 40 %) and/or vesicle diameter (from 0.1 to 2.0 mm) results in a dramatic reduction in strength. For example, uniaxial compressive strength can be reduced by about a factor of 5 as porosity is increased from 0 to 40 %. The presence of vesicles locally amplifies the stress within the groundmass and promotes the nucleation of vesicle-emanating microcracks that grow in the direction of the applied macroscopic stress. As strain increases, these microcracks continue to grow and eventually coalesce leading to macroscopic failure. Vesicle clustering, which promotes the overlap and interaction of the tensile stress lobes at the north and south poles of neighbouring vesicles, and the increased ease of microcrack interaction, is encouraged at higher porosity and reduces sample strength. Once a microcrack nucleates at the vesicle wall, larger vesicles impart higher stress intensities at the crack tips, allowing microcracks to propagate at a lower applied macroscopic stress. Larger vesicles also permit a shorter route through the groundmass for the macroscopic shear fracture. This explains the reduction in strength at higher vesicle diameters (at a constant porosity). The modelling highlights that the reduction in strength as porosity or vesicle size increases is nonlinear; the largest reductions are observed at low porosity and small vesicle diameters. In detail, we find that vesicle diameter can play an important role in dictating strength at low porosity but is largely inconsequential above 15 % porosity. Vesicle clustering and stress lobe interaction are implicit at high porosity, regardless of the vesicle diameter. In the case of an inhomogeneous vesicle size, the microcracks grow from the largest vesicles, and brittle strength is closer to that of the largest vesicle end-member. The results of this study highlight the important role of vesicle size, and the complex interplay between porosity and vesicle size, in controlling the brittle strength of volcanic rocks and magma.
Thermal Storage and Transport Properties of Rocks, I: Heat Capacity and Latent Heat
题名：岩石的热储与运移特性：热容量与潜热
Encyclopedia of Solid Earth Geophysics, Encyclopedia of Earth Sciences Series 2014, pp 1423-1431
Visualization of the complex structure and stress field inside rock by means of 3D printing technology
题名：用3D打印技术可视化岩石复合结构与引力场
Chinese Science Bulletin, August 2014
Abstract: Accurate characterization and visualization of the complex inner structure and stress distribution of rocks are of vital significance to solve a variety of underground engineering problems. In this paper, we incorporate several advanced technologies, such as CT scan, three-dimensional (3D) reconstruction, and 3D printing, to produce a physical model representing the natural coal rock that inherently contains complex fractures or joints. We employ 3D frozen stress and photoelastic technologies to characterize and visualize the stress distribution within the fractured rock under uniaxial compression. The 3D printed model presents the fracture structures identical to those of the natural prototype. The mechanical properties of the printed model, including uniaxial compression strength, elastic modulus, and Poisson’s ratio, are testified to be similar to those of the prototype coal rock. The frozen stress and photoelastic tests show that the location of stress concentration and the stress gradient around the discontinuous fractures are in good agreement with the numerical predictions of the real coal sample. The proposed method appears to be capable of visually quantifying the influences of discontinuous, irregular fractures on the strength, deformation, and stress concentration of coal rock. The method of incorporating 3D printing and frozen stress technologies shows a promising way to quantify and visualize the complex fracture structures and their influences on 3D stress distribution of underground rocks, which can also be used to verify numerical simulations.
Block caving-induced strata movement and associated surface subsidence: a numerical study based on a demonstration model
题名：矿块崩落法开采引起的地层移动与地表沉降：基于示范模型的数值研究
Bulletin of Engineering Geology and the Environment, August 2014
Abstract: The block cave mining mechanism and associated subsidence present one of the most challenging engineering problems in rock mining. Although block caving has been in use for many years, there has been limited research on the impact caving angles have on surface settlement and failure profiles, specifically when associated with deep caves and surface propagation (i.e., not as part of caving into an existing open pit). We analyse in this study block caving-induced step-path failure development in a large-scale demonstration model utilizing a numerical code based on a finite element technique that incorporates an elasto-brittle fracture mechanics constitutive criterion. Fracture initiation, propagation and coalescence, as well as the breaking of the intact rock bridge and the evolution of a pressure-balancing arch in the stressed strata, are represented visually during the whole caving process. Based on numerical results, surface impacts of block caving, such as subsidence profiles, break angles, fracture initiation angles and subsidence angles at different initial caving depths, are illustrated in this study.
Effect of rock strength on failure mode and mechanical behavior of composite samples
题名：岩石强度对复合煤岩样破坏模式及力学性能的影响
Arabian Journal of Geosciences, August 2014
Abstract: Many dynamic events in coal mine are caused by the instability of coal–rock body. In order to study the influence of rock strength on this type of instability, uniaxial compression experiments of rock–coal–rock composite samples with different rock strengths are carried out, and the effect and mechanism of rock strength on the mechanical behavior and fracture mode of the composite samples are analyzed. The results show that major failure modes of the composite samples are conjugate X-shaped shearing fracture and splitting fracture. The angle between the shear fracture surface and the end face increases with rock strength. The splitting fracture in the coal body expands to the rock when the rock strength is low. The strength properties of the composite samples mainly depend on the coal strength instead of the rock strength. With the rock strength increasing, the peak strain of the composite samples decrease, and the differences from the coal strain and strain rate to rock strain and strain rate become greater. These failure modes and characteristics of deformation are shown to be determined by the difference between the elastic modulus of rock and coal constituting the composite samples.
Fracture Angle Analysis of Rock Burst Faulting Planes Based on True-Triaxial Experiment
题名：基于真三轴实验的岩爆断层面断裂角分析
Rock Mechanics and Rock Engineering, August 2014
Abstract: The aim of this paper is to estimate fracture angles in deep-seated rock bursts encountered in intact hard rock tunnels. The fracture angles of fault planes in rock burst failure are analytically formulated by employing stress analysis based on Mohr’s circle construction. Mohr’s circle construction suits well for representing the rock burst stress states including the static loading and dynamic unloading processes existing at or near the excavation surface. Four fracture angles can be precisely predicted using the proposed mathematical models, including two minimum angles for two conjugate planes where the shear stress is equal to the maximum static shear stress τ max while the normal stress approaches to zero, and two maximum angles for two conjugate planes where the normal stress is reduced from σ 1 to σ 1/2 while shear stress increases markedly from ±(σ 1–σ 3)/2 to the maximum dynamic shear τ dmax = ±σ 1/2. For validation of the analytical solutions to fracture angles, rock burst experiments on Laizhou granite were conducted using a modified true-triaxial apparatus. The predicted fracture angles are compared very well with the results obtained from the laboratory rock burst tests and are in good agreement with the in situ observations. The proposed solutions to the fracture angle are a function of the static stresses only which can be known a priori from a field survey.
