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Rock dynamics in deep mining

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International Journal of Mining Science and Technology 2023年第9期33卷 1065-1082页

作者： Manchao He Qi Wang state key laboratory for geo-mechanics and deep underground engineering China University of Mining&Technology-BeijingBeijing 100083China

Rock mass dynamics disasters caused by excavations and mining occur frequently in deep *** order to establish a theoretical system and control technologies for such disasters,we first classify and define dynamic disasters,such as rock bursts,coal bursts,mine pressure bumps,and mine *** to the occurrence mechanism of different types of dynamic disasters,we establish a compensation control theory based on excavation and mining *** the basis,we propose three key technologies:high prestress compensation technology for the roadway,pressure relief technology using directional roof cutting,and the goaf filling technology using broken rock *** three technologies constitute the compensation control method for dynamic disasters in deep ***,this method was successfully applied in a deep coal mine with high stress,with monitored results suggesting its *** work provides a new concept and control method for the prevention of rock dynamic disasters in deep mines.

关键词： Rock burst Coal burst Mine pressure bump Mine earthquake Excavation compensation control Mining compensation control

Strength and failure characteristics of brittle jointed rock-like specimens under uniaxial compression:Digital speckle technology and a particle mechanics approach

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International Journal of Mining Science and Technology 2018年第4期28卷 662-670页

作者： Rihong Cao Hang Lin Ping Cao School of Resources and Safety engineering Central South University state key laboratory for geo mechanics and deep underground engineering China University of Mining & Technology

The strength and failure characteristics of most natural rock mass are influenced by discontinues such as fissures, joints, and weak surfaces. In the present study, the strength and failure behavior of ubiquitous- joint rock-l!ke specimens under uniaxial loading have been investigated by DIC （digital image correlation） and discrete element numerical method （PFC2D）. The results are obtained. Firstly, the UCSJ of spec- imens with γ= 15° or 30° shows similar tendency while α goes from 0° to 75°. With γ= 45° or 60°, the UCSJ of specimens increases when α goes from 0° to 30° and decreases after α goes beyond 30°. With γ=75°, the peak UCSJ value is reached when α=0°. The UCSJ value shows an increasing trend when α goes from 60° to 75°. Secondly, the ubiquitous-joint specimens present different failure modes for various levels of α and γ（β-α）. Based on the experimental results, the failure mode of ubiquitous-joint specimens can be classified into three categories： stepped path failure, failure through parallel plane, and failure through cross plane.

关键词： Ubiquitous-joint Digital speckle correlation technique PFC2D Strength Failure mode

Fractal characteristics of cracks and fragments generated in unloading rockburst tests

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International Journal of Mining Science and Technology 2014年第6期24卷 819-823页

作者： Li Dejian Zhao Fei Zheng Maojiong state key laboratory of geo mechanics and deep underground engineering School of Civil engineering China University of Mining & Technology

True triaxial rockburst experiments with four different unloading rates were performed on four prism specimens of granite sampled from Beishan, China. The damage evolution in the rockburst test was investigated from two aspects including fracture surface crack and fragment characteristics. The scanning electron microscopy was used to observe the micro crack information on fragment surface. Combing binarization and box counting dimensions, the fractal dimensions of cracks were obtained. Meanwhile,the fragments were collected and a sieving experiment was conducted. We weighed the fragments qualities, counted the amount of fragments and measured the fragments length, width and *** four methods to calculate damage fractal dimensions of fragments, the trend of fractal value changing with unloading rates can be roughly described. It can be concluded from these experiments that the fractal dimension either for crack or for fragment holds a decreasing trend with the decreasing unloading rate, indicating a reduction of damage level.

关键词： Unloading rockburst test Fragments Grain distribution Micro crack Fractal dimension

Experimental and numerical study on loading rate effects of rock-like material specimens containing two unparallel fissures

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Journal of Central South University 2016年第6期23卷 1474-1485页

作者：黄彦华杨圣奇曾卫 state key laboratory for geomechanics and deep underground engineering School of Mechanics and Civil Engineering China University of Mining and Technology

A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried *** the basis of experimental and numerical results,the stress-strain curves,mechanical properties,AE events,cracking behavior and energy characteristics were analyzed to reveal the macro-mechanical behavior and meso-mechanism of pre-fissured specimens under different loading *** results show that:1)When the loading rate is relatively low,the stress-strain curves show a brittle *** the loading rate is relatively high,the curve shows a more ductile *** of the peak strength and elastic mudulus increase with the increase of loading rate,which can be expressed as power functions.2)Four crack types are identified,i.e.,tensile crack,shear crack,far-field crack and surface ***,the tensile crack,far-field crack and surface spalling are under tensile mechanism,while the shear crack is under shear mechanism.3)The drops of the stress-strain curves all correspond to the crack initiation or coalescence,which is also linked to a sudden increasing in the accumulated micro-crack curve.4)Both of the maximum bond force and energy have the similar trend with the increase of loading rate to peak strength,which indicates that the trend of peak strength can be explained by the meso-mechanics and energy.

关键词： rock mechanics two pre-existing fissures strength parameters crack coalescence particle flow simulation

New true-triaxial rock strength criteria considering intrinsic material characteristics

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Acta Mechanica Sinica 2018年第1期34卷 130-142页

作者： Qiang Zhang Cheng Li Xiaowei Quan Yanning Wang Liyuan Yu Binsong Jiang state key laboratory for geomechanics and deep underground engineering School of Mechanics and Civil Engineering China University of Mining and Technology

A reasonable strength criterion should reflect the hydrostatic pressure effect, minimum principal stress effect,and intermediate principal stress effect. The former two effects can be described by the meridian curves, and the last one mainly depends on the Lode angle dependence function. Among three conventional strength criteria, ***–Coulomb(MC), Hoek–Brown(HB), and Exponent(EP) criteria, the difference between generalized compression and extension strength of EP criterion experience a firstly increase then decrease process, and tends to be zero when hydrostatic pressure is big enough. This is in accordance with intrinsic rock strength characterization. Moreover, the critical hydrostatic pressure Icorresponding to the maximum difference of between generalized compression and extension strength can be easily adjusted by minimum principal stress influence parameter K. So, the exponent function is a more reasonable meridian curves, which well reflects the hydrostatic pressure effect and is employed to describe the generalized compression and extension ***, three Lode angle dependence functions of L,L, and L, which unconditionally satisfy the convexity and differential requirements, are employed to represent the intermediate principal stress effect. Realizing the actual strength surface should be located between the generalized compression and extension surface, new true-triaxial criteria are proposed by combining the two states of EP criterion by Lode angle dependence function with a same lode angle. The proposed new true-triaxial criteria have the same strength parameters as EP criterion. Finally, 14 groups of triaxial test data are employed to validate the proposed criteria. The results show that the three new true-triaxial exponent criteria,especially the Exponent Willam-Warnke criterion(EPWW)criterion, give much lower misfits, which illustrates that the EP criterion and Lhave more reasonable meridian and deviatoric function form, respectively.

关键词： Rock Strength criterion Meridian plane Lode angle dependence Convexity

Impact of cooling rate on mechanical properties and failure mechanism of sandstone under thermal-mechanical coupling effect

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International Journal of Coal Science & Technology 2023年第2期10卷 97-116页

作者： Pingye Guo Peng Zhang Mohua Bu Hang Xing Manchao He state key laboratory for geo-mechanics and deep underground engineering Beijing 100083China School of mechanics and Civil engineering China University of Mining and TechnologyBeijing 100083China

High geo-temperature is one of the inevitable geological disasters in deep engineering such as resource extraction,space development,and energy *** of the key issues is to understand the mechanical properties and failure mechanism of high-temperature rock disturbed by low-temperature airflow after ***,.the experimental and numerical investigation were carried out to study the impact of cooling rate on mechanical properties and failure mechanism of high temperature ***,uniaxial compression experiments of high temperature sandstone at different real-time cooling rates were carried out to study the mechanical properties and failure *** experimental results indicate that the cooling rate has a significant effect on the mechanical properties and failure modes of *** peak strain,peak stress,and elastic modulus decrease with an increase in cooling rate,and the fragmentation degree after failure increases ***,the equivalent numerical model of heterogeneous sandstone was established using particle flow code(PFC)to reveal the failure *** results indicate that the sandstone is dominated by intragrain failure in the cooling stage,the number of microcracks is exponentially related to the cooling rate,and the higher the cooling rate,the more cracks are concentrated in the exterior *** axial loading,the tensile stress is mostly distributed along the radial direction,and the damage in the cooling stage is mostly due to the fracture of the radial *** addition,axial loading,temperature gradient and thermal stress mismatch between adjacent minerals are the main reasons for the damage of sandstone in the cooling ***,the excessive temperature gradient in the exterior region of the sandstone is the main reason for the damage concentration in this region.

关键词： High geo-temperature Thermo-mechanical coupling effect Cooling rate Sandstone PFC

Particle flow study on strength and meso-mechanism of Brazilian splitting test for jointed rock mass

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Acta Mechanica Sinica 2014年第4期30卷 547-558页

作者： Sheng-Qi Yang Yan-Hua Huang state key laboratory for geomechanics and deep underground engineering School of Mechanics and Civil EngineeringChina University of Mining and Technology

A discrete element method （DEM） called particle flow code （PFC2D） was used to construct a model for Brazilian disc splitting test in the present study. Based on the experimental results of intact Brazilian disc of rock-like material, a set of micro-parameters in PFC2D that reflected the macro-mechanical behavior of rock-like materials were obtained. And then PFC2D was used to simulate Brazilian splitting test for jointed rock mass specimens and specimen containing a central straight notch. The effect of joint angle and notch angle on the tensile strength and failure mode of jointed rock specimens was detailed analyzed. In order to reveal the meso-mechanical mechanism of crack coalescence, displacement trend lines were applied to analyze the displacement evolution during the crack initiation and propagation. The investigated conclusions can be described as follows. （1） The tensile strength of jointed rock mass disc specimen is dependent to the joint angle. As the joint angle increases, the tensile strength of jointed rock specimen takes on a nonlinear variance. （2） The tensile strength of jointed rock mass disc specimen containing a central straight notch distributes as a function of both joint angle and notch angle. （3） Three major failure modes, i.e., pure tensile failure, shear failure and mixed tension and shear failure mode are observed in jointed rock mass disc specimens under Brazilian test. （4） The notch angle roles on crack initiation and and joint angle play important propagation characteristics of jointed rock mass disc specimen containing a central straight notch under Brazilian test.

关键词： Jointed rock mass Brazilian splitting test. Ten-sile strength· Failure mode PFC2D

Rockburst mechanism research and its control

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International Journal of Mining Science and Technology 2018年第5期28卷 829-837页

作者： Manchao He Fuqiang Ren Dongqiao Liu state key laboratory for geomechanics & deep underground engineering School of Mechanics and Civil Engineering China University of Mining & TechnologyBeijing

A new rockburst classification, innovative works in developing a ‘‘strainburst test machine" and an‘‘impact-induced rockburst test machine" that can reproduce rockbursts in laboratory were *** concepts were proposed regarding the stress paths that take into account both the static and dynamic stresses analogous to that at excavation boundaries for generating artificially-induced strainburst and impact-induced rockburst. As an important method for rockburst control, a novel energyabsorbing bolt was developed, which has a constant-resistance under both static and impact loadings and a large-elongation capacity for containing large deformations of rock masses under burst-prone conditions.

关键词： Rockburst Stress paths Energy-absorbing bolt Rockburst control

Dynamic responses of deep underground explosions based on improved Grigorian model

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Journal of Central South University 2015年第1期22卷 323-331页

作者：陈万祥范新郭志昆王明洋 state key laboratory of Disaster Prevention & Mitigation of Explosion & Impact(PLA University of Science and Technology) state key laboratory for geo mechanics & deep underground engineering(China University of Mining and Technology) The Second Artillery Command Academy

It is important to investigate the dynamic behaviors of deep rocks near explosion cavity to reveal the mechanisms of deformations and fractures. Some improvements are carried out for Grigorian model with focuses on the dilation effects and the relaxation effects of deep rocks, and the high pressure equations of states with Mie-Grüneisen form are also established. Numerical calculations of free field parameters for deep underground explosions are carried out based on the user subroutines which are compiled by means of the secondary development functions of LS-DYNA9703 D software. The histories of radial stress, radial velocity and radial displacement of rock particles are obtained, and the calculation results are compared with those of U.S. Hardhat nuclear test. It is indicated that the dynamic responses of free field for deep underground explosions are well simulated based on improved Grigorian model, and the calculation results are in good agreement with the data of U.S. Hardhat nuclear test. The peak values of particle velocities are consistent with those of test, but the waveform widths and the rising times are obviously greater than those without dilation effects. The attenuation rates of particle velocities are greater than the calculation results with classic plastic model, and they are consistent with the results of Hardhat nuclear test. The attenuation behaviors and the rising times of stress waves are well shown by introducing dilation effects and relaxation effects into the calculation model. Therefore, the defects of Grigorian model are avoided. It is also indicated that the initial stress has obvious influences on the waveforms of radial stress and the radial displacements of rock particles.

关键词： underground explosion deep rock Grigorian model numerical calculation dynamic response