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Effects of loading waveforms on rock damage using particle simulation method

Journal of Central South University 2018年第7期25卷 1755-1765页

作者： XIA Ming gong feng-qiang Hunan Key Laboratory of Geomechanics and Engineering Safety Xiangtan UniversityXiangtan 411105China College of Civil Engineering and Mechanics Xiangtan UniversityXiangtan 411105China School of Resources and Safety Engineering Central South UniversityChangsha 410083China

The particle simulation method is used to study the effects of loading waveforms （i.e. square, sinusoidal and triangle waveforms） on rock damage at mesoscopic scale. Then some influencing factors on rock damage at the mesoscopic scale, such as loading frequency, stress amplitude, mean stress, confining pressure and loading sequence, are also investigated with sinusoidal waveform in detail. The related numerical results have demonstrated that： 1） the loading waveform has a certain effect on rock failure processes. The square waveform has the most damage within these waveforms, while the triangle waveform has less damage than sinusoidal waveform. In each cycle, the number of microscopic cracks increases in the loading stage, while it keeps nearly constant in the unloading stage. 2） The loading frequency, stress amplitude, mean stress, confining pressure and loading sequence have considerable effects on rock damage subjected to cyclic loading. The higher the loading frequency, stress amplitude and mean stress, the greater the damage the rock accumulated; in contrast, the lower the confining pressure, the greater the damage the rock has accumulated. 3） There is a threshold value of mean stress and stress amplitude, below which no further damage accumulated after the first few cycle loadings. 4） The high-to-low loading sequence has more damage than the low-to-high loading sequence, suggesting that the rock damage is loading-path dependent.

关键词： rock damage failure process crack initiation and propagation loading waveform cycle loading particle simulation method

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Brazilian disc test study on tensile strength-weakening effect of high pre-loaded red sandstone under dynamic disturbance

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Journal of Central South University 2020年第10期27卷 2899-2913页

作者： gong feng-qiang WU Wu-xing ZHANG Le Engineering Research Center of Safety and Protection of Explosion&Impact of Ministry of Education(ERCSPEIME) Southeast UniversityNanjing 211189China School of Civil Engineering Southeast UniversityNanjing 211189China School of Resources and Safety Engineering Central South UniversityChangsha 410083China

Tensile failure(spalling or slabbing)often occurs on the sidewall of deep tunnel,which is closely related to the coupled stress state of deep rock mass under high pre-static load and dynamic *** reveal the mechanism of rock tensile failure caused by this coupled stress mode,the Brazilian disc tests were carried on red sandstone under high pre-static load induced by dynamic *** on the pure static tensile fracture load of red sandstone specimen,two static load levels(80%and 90%of the pure static tensile fracture load)were selected as the initial high pre-static loading state,and then the dynamic disturbance load was applied until the rock specimen was *** dynamic disturbance loading mode adopted a sinusoidal wave(sine-wave)load,and the loading wave amplitude was 20%and 10%of the pure static tensile fracture load,*** dynamic disturbance frequencies were set to 1,10,20,30,40,and 50 *** results show that the tensile failure strength and peak displacement of red sandstone specimens under coupled load actions are lower than those under pure static tensile load,and both parameters decrease significantly with the increase of dynamic disturbance *** the increase of dynamic disturbance frequency,the decrease range of tensile strength of red sandstone increased from 3.3%to 9.4%when the pre-static load level is 80%.While when the pre-static load level is 90%,the decrease range will increase from 7.4%to 11.6%.This weakening effect of tensile strength shows that the deep surrounding rock is more likely to fail under the coupled load actions of pre-static load and dynamic *** this tensile failure mechanism of the deep surrounding rock,the stress environment of deep sidewall rock determines that the failure mode of rock is a tensile failure,the pre-static load level dominates the tensile failure strength of surrounding rock,and dynamic disturbance promotes the strength-weakening effect and affects the weakening

关键词： spalling deep surrounding rock strength-weakening effect pre-static load dynamic disturbance tensile failure Brazilian disc test

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Rockburst proneness criteria for rock materials:Review and new insights

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Journal of Central South University 2020年第10期27卷 2793-2821页

作者： gong feng-qiang WANG Yun-liang LUO Song School of Resources and Safety Engineering Central South UniversityChangsha 410083China School of Civil Engineering Southeast UniversityNanjing 211189China

To review the rockburst proneness(or tendency)criteria of rock materials and compare the judgment accuracy of them,twenty criteria were summarized,and their judgment accuracy was evaluated and compared based on the laboratory tests on fourteen types of *** study begins firstly by introducing the twenty rockburst proneness criteria,and their origins,definitions,calculation methods and grading standards were summarized in ***,to evaluate and compare the judgment accuracy of the twenty criteria,a series of laboratory tests were carried out on fourteen types of rocks,and the rockburst proneness judgment results of the twenty criteria for the fourteen types of rocks were obtained ***,to provide a unified basis for the judgment accuracy evaluation of above criteria,a classification standard(obtained according to the actual failure results and phenomena of rock specimen)of rockburst proneness in laboratory tests was *** judgment results of the twenty criteria were compared with the judgment results of this classification *** results show that the judgment results of the criterion based on residual elastic energy(REE)index are completely consistent with the actual rockburst proneness,and the other criteria have some inconsistent situations more or ***,the REE index is based on the linear energy storage law and defined in form of a difference value and considered the whole failure process,and these superior characteristics ensure its *** is believed that the criterion based on REE index is comparatively more accurate and scientific than other criteria,and it can be recommended to be applied to judge the rockburst proneness of rock materials.

关键词： deep rock rockburst rockburst proneness rockburst proneness criterion rock mechanics

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Experimental study on energy storage and dissipation characteristics of granite under two-dimensional compression with constant confining pressure

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Journal of Central South University 2021年第3期28卷 848-865页

作者： SU You-qiang gong feng-qiang LUO Song LIU Zhi-xiang School of Resources and Safety Engineering Central South UniversityChangsha 410083China School of Civil Engineering Southeast UniversityNanjing 211189China

To study the energy storage and dissipation characteristics of deep rock under two-dimensional compression with constant confining pressure,the single cyclic loading-unloading two-dimensional compression tests were performed on granite specimens with two height-to-width(H/W)ratios under five confining *** energy density parameters(input energy density,elastic energy density and dissipated energy density)in the axial and lateral directions of granite specimens under different confining pressures were calculated using the area integral *** experimental results show that,for the specimens with a specific H/W ratio,these three energy density parameters in the axial and lateral directions increase nonlinearly with the confining pressure as quadratic polynomial *** constant confining pressure compression,the linear energy storage law of granite specimens in the axial and lateral directions was *** the linear energy storage law in different directions,the elastic energy density in various directions(axial elastic energy density,lateral elastic energy density and total elastic energy density)of granite under any specific confining pressures can be *** the H/W ratio varies from 1:1 to 2:1,the lateral compression energy storage coefficient increases and the corresponding axial compression energy storage coefficient decreases,while the total compression energy storage coefficient is almost independent of the H/W ratio.

关键词： rock mechanics two-dimensional compression linear energy storage law single cyclic loading-unloading height-to-width ratio

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Experimental simulation investigation of influence of depth on spalling characteristics in circular hard rock tunnel

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Journal of Central South University 2020年第3期27卷 891-910页

作者： LUO Yong gong feng-qiang LI Xi-bing WANG Shan-yong School of Resources Environment and Safety Engineering University of South ChinaHengyang 421001China School of Resources and Safety Engineering Central South UniversityChangsha 410083China School of Civil Engineering Southeast UniversityNanjing 211189China ARC Centre of Excellence for Geotechnical Science and Engineering Faculty of Engineering and Built EnvironmentThe University of NewcastleCallaghanNSW 2238Australia

A series of true-triaxial compression tests were performed on red sandstone cubic specimens with a circular hole to investigate the influence of depth on induced spalling in *** failure process of the hole sidewalls was monitored and recorded in real-time by a micro-video monitoring *** general failure evolution processes of the hole sidewall at different initial depths(500 m,1000 m and 1500 m)during the adjustment of vertical stress were *** results show that the hole sidewall all formed spalling before resulting in strain rockburst,and ultimately forming a V-shaped *** far-field principal stress for the initial failure of the tunnel shows a good positive linear correlation with the *** the depth increases,the stress required for the initial failure of the tunnels clearly increased,the spalling became more intense;the size and mass of the rock fragments and depth and width of the V-shaped notches increased,and the range of the failure zone extends along the hole sidewall from the local area to the entire ***,as the depth increases,the support area around the tunnel should be increased accordingly to prevent spalling.

关键词： deep underground engineering circular tunnels spalling strain rockburst true-triaxial loading V-shaped notch

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Dynamic characteristics of high stressed red sandstone subjected to unloading and impact loads

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Journal of Central South University 2022年第2期29卷 596-610页

作者： gong feng-qiang ZHONG Wen-hui GAO Ming-zhong SI Xue-feng WU Wu-xing School of Resources and Safety Engineering Central South UniversityChangsha 410083China School of Civil Engineering Southeast UniversityNanjing 211189China Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization Shenzhen UniversityShenzhen 518060China

In the process of deep projects excavation,deep rock often experiences a full stress process from high stress to unloading and then to impact disturbance *** study the dynamic characteristics of three-dimensional high stressed red sandstone subjected to unloading and impact loads,impact compression tests were conducted on red sandstone under confining pressure unloading conditions using a modified split Hopkinson pressure *** disturbance tests of uniaxial pre-stressed rock were also conducted(without considering confining pressure unloading effect).The results demonstrate that the impact compression strength of red sandstone shows an obvious strain rate *** an approximately equal strain rate,the dynamic strength of red sandstone under confining unloading conditions is less than that in the uniaxial pre-stressed impact compression *** pressure unloading produces a strength-weakening effect,and the dynamic strength weakening factor(DSWF)is also *** results also indicate that the strain rate of the rock and the incident energy change in a logarithmic *** similar incident energies,unloading results in a higher strain rate in pre-stressed *** to the experimental analysis,unloading does not affect the failure mode,but reduces the dynamic strength of pre-stressed *** influence of confining pressure unloading on the shear strength parameters(cohesion and friction angle)is *** the same external energy impact compression,prestressed rock subjected to unloading is more likely to be ***,the effect of unloading on the rock mechanical characteristics should be considered in deep rock project excavation design.

关键词： deep rock excavation unloading unloading confining pressure three-dimensional high stress strengthweakening effect impact disturbance

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Experimental investigation on influence of loading rate on rockburst in deep circular tunnel under true-triaxial stress condition

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Journal of Central South University 2020年第10期27卷 2914-2929页

作者： SI Xue-feng HUANG Lin-qi gong feng-qiang LIU Xi-ling LI Xi-bing School of Resources and Safety Engineering Central South UniversityChangsha 410083China School of Civil Engineering Southeast UniversityNanjing 211189China

To investigate the influence of loading rate on rockburst in a circular tunnel under three-dimensional stress conditions,the true-triaxial tests were conducted on 100 mm×100 mm×100 mm cubic sandstone specimens with d50 mm circular perforated holes,and the failure process of hole sidewall was monitored and recorded in real-time by the *** loading rates were 0.02,0.10,and 0.50 MPa/*** test results show that the rockburst process of hole sidewall experienced calm period,pellet ejection period,rock fragment exfoliation period and finally formed the V-shaped *** rockburst has a time lag and vertical stress is high when the rockburst *** vertical stress at the initial failure of the hole sidewall increases with loading *** the same period after initial failure,the rockburst severity of hole sidewalls increased significantly with increasing loading *** the vertical stress is constant and maintains a high stress level,the rockburst of hole sidewall under low loading rate is more serious than that under high loading *** increasing loading rate,the quality of rock fragments produced by the rockburst decreases,and the fractal dimension of rock fragments increases.

关键词： rockburst loading rate deep circular tunnel true-triaxial test V-shaped notch

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Effect of loading rate on fracture behaviors of shale under mode I loading

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Journal of Central South University 2020年第10期27卷 3118-3132页

作者： XIE Qin LI Sheng-xiang LIU Xi-ling gong feng-qiang LI Xi-bing School of Resources and Safety Engineering Central South UniversityChangsha 410083China School of Civil Engineering Southeast UniversityNanjing 211189China

In this study,the effect of loading rate on shale fracture behaviors was investigated under dynamic and static loading *** straight through Brazilian disc(CSTBD)shale specimens were tested with a split Hopkinson pressure bar(SHPB)setup and INSTRON1346 servo-testing machine under pure mode I loading *** the test,the crack propagation process was recorded by high-speed(HS)camera,and the acoustic emission(AE)signal generated by the fracture was collected by acoustic emission(AE)*** the same time,crack propagation gauge(CPG)was used to measure the crack propagation velocity of the *** results show that the crack propagation velocity and fracture toughness of shale have a positive correlation with the loading *** relationship among the crack propagation velocity,the fracture toughness and the loading rate is established under the static loading *** addition,the characteristics of AE signals with different loading rates are *** is found that the AE signals generated by microcrack growth decrease with the increase of loading ***,the turning point of cumulative counting moves forward as the loading rate increases,which shows that the AE signal generated by shale fracture at low loading rate mainly comes from the initiation and propagation of microcracks,while at high loading rate it mainly comes from the formation of macro large-scale *** fracture mechanism that causes shale fracture toughness and crack propagation velocity to vary with loading rate is also discussed based on the analysis results of AE signals.

关键词： shale loading rate cracked straight through Brazilian disc fracture toughness acoustic emission crack propagation velocity

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膨胀土胀缩等级分类中的距离判别分析法

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岩土工程学报 2007年第3期29卷 463-466页

作者：宫凤强李夕兵中南大学资源与安全工程学院湖南长沙410083

膨胀土胀缩等级的分类是治理膨胀土工作中的首要问题。本文将距离判别分析方法应用于膨胀土胀缩等级的分类问题中,建立了膨胀土胀缩等级分类的距离判别分析模型,选用黏粒含量、粉粒含量、液限、塑限和塑性指数5项指标作为距离判别分析... 详细信息

膨胀土胀缩等级的分类是治理膨胀土工作中的首要问题。本文将距离判别分析方法应用于膨胀土胀缩等级的分类问题中,建立了膨胀土胀缩等级分类的距离判别分析模型,选用黏粒含量、粉粒含量、液限、塑限和塑性指数5项指标作为距离判别分析模型的判别因子,以膨胀土实测数据作为学习样本进行训练,建立相应线性判别函数对待判样本进行分类。研究结果表明:距离判别分析模型分类性能良好,预测精度高,交叉确认估计的误判率很低,是膨胀土胀缩等级分类的一种有效方法,可以在实际工程中进行推广。

关键词：膨胀土距离判别分析分类

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矿区立井井筒非采动破裂的距离判别分析预测法

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煤炭学报 2007年第7期32卷 700-704页

作者：宫凤强李夕兵中南大学资源与安全工程学院湖南长沙410083

将距离判别分析方法应用于矿区立井井筒非采动破裂的预测问题中,建立了井筒非采动破裂的距离判别分析模型.选用表土层厚度、底含厚度、底含水位速降、井筒外径、井壁厚度和井筒投入使用时间6项指标作为距离判别分析模型的判别因子,以历... 详细信息

将距离判别分析方法应用于矿区立井井筒非采动破裂的预测问题中,建立了井筒非采动破裂的距离判别分析模型.选用表土层厚度、底含厚度、底含水位速降、井筒外径、井壁厚度和井筒投入使用时间6项指标作为距离判别分析模型的判别因子,以历史上工程实测数据作为学习样本进行训练,建立相应判别函数对工程实例进行预测.研究结果表明,距离判别分析模型分类性能良好,预测精度高,回判估计的误判率很低.

关键词：立井井筒非采动破裂距离判别分析

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