Mechanical and damage evolution properties of sandstone under triaxial compression

To study the mechanical and damage evolution properties of sandstone under triaxial compression,we analyzed the stress strain curve characteristics,deformation and strength properties,and failure process and characteristics of sandstone samples under different stress states.The experimental results reveal that peak strength,residual strength,elasticity modulus and deformation modulus increase linearly with confining pressure,and failure models transform from fragile failure under low confining pressure to ductility failure under high confining pressure.Macroscopic failure forms of samples under uniaxial compression were split failure parallel to the axis of samples,while macroscopic failure forms under uniaxial compression were shear failure,the shear failure angle of which decreased linearly with confining pressure.There were significant volume dilatation properties in the loading process of sandstone under different confining pressures,and we analyzed the damage evolution properties of samples based on acoustic emission damage and volumetric dilatation damage,and established damage constitutive model,realizing the real-time quantitative evaluation of samples damage state in loading process.     

碳化高温后再生混凝土受压声发射特性与损伤演化

为研究再生混凝土在碳化高温下的损伤演化规律,对碳化后不同温度梯度（常温20 ℃、中低温200 ℃及中高温400 ℃）下C30再生混凝土（质量分数取代率0%、50%、100%）进行轴心受压试验并同步采集声发射信号,在分析声发射特征参数的基础上建立再生混凝土的损伤模型。结果表明,通过对声发射损伤定位、累计撞击计数与能量计数分析,可实现再生混凝土轴心受压破坏从初始损伤到微裂缝演变,再到宏观裂缝扩展,最终到试件破坏的全过程动态监测;不同粗骨料取代率再生混凝土试件,加载过程中损伤点的密集集中位置与试件最终破坏位置相符;随着温度梯度增加,3种不同粗骨料取代率的再生混凝土均呈现初始损伤增大、声发射参数增大、应力减小的现象;基于声发射累计撞击计数建立的混凝土损伤模型可用于分析碳化高温后再生混凝土轴心受压损伤演化规律。     

三轴压缩下粉砂质泥岩蠕变力学特性试验研究

为揭示三峡地区巴东组二段粉砂质泥岩的蠕变力学特性,采用RLJW-2000岩石流变伺服仪对饱和粉砂质泥岩进行了三轴压缩蠕变试验。试验在分级加载条件下进行,试验围压为1 MPa。基于试验结果,定量研究了粉砂质泥岩蠕变过程中轴向蠕应变与径向蠕应变的差异、轴向蠕变速率与径向蠕变速率的差异,得出了岩石的长期强度。研究结果表明:1)在各级应力水平下,试样径向蠕应变占径向总应变的比例始终比轴向蠕应变占轴向总应变的比例大,岩石的径向蠕变效应更明显。2)在破裂应力水平下,岩石径向蠕变比轴向蠕变先进入加速蠕变阶段,径向的初始蠕变速率、稳态蠕变速率以及加速蠕变速率均高于轴向相应的蠕变速率,以径向蠕变特征来判别粉砂质泥岩是否发生蠕变破坏更合理。工程实践中,应加强对岩石径向蠕变特性的监测工作,这对于工程失稳的预测预报更有意义。3)粉砂质泥岩的长期强度仅为其瞬时强度的74.4%,长期强度折减较大。4)试验中获得的长期强度实际上应为粉砂质泥岩的径向长期强度,径向先发生蠕变破坏从而导致试样破坏。     

Acoustic emission characteristics of rock under impact loading

Acoustic emission tests were performed using a split Hopkinson pressure bar system(SHPB) on 50-mm-diameter bars of granite, limestone, sandstone and skarn. The results show that the amplitude distribution of hits is not well centralized around 50 d B, and that some hits with large amplitudes, usually larger than 70 d B, occur in the early stages of each test, which is different from the findings from static and low-loading-rate tests. Furthermore, the dominant frequency range of the recorded acoustic emission waveforms is between 300 k Hz and 500 k Hz, and frequency components higher than 500 k Hz are not significant. The hit with the largest values of amplitude, counts, signal strength, and absolute energy in each test, displays a waveform with similar frequency characteristics and greater correlation with the waveform obtained from the elastic input bar of the split Hopkinson pressure bar system compared with the waveforms of the other hits. This indicates that the hit with the largest values of amplitude, counts, signal strength, and absolute energy is generated by elastic wave propagation instead of fracture within the rock specimen.     

三轴卸荷条件下煤体力学特性和能量耗散演化

孤岛工作面煤体和巷道受周边开采扰动影响,煤体受循环荷载作用存在卸荷力学行为而表现出动态破坏特性.为探讨不同路径下煤体力学特性,利用TAW-2000三轴电液伺服刚性试验机分别进行常规三轴(T)、三轴循环荷载(TC)以及相应卸围压试验(TU、TCU),分析不同围压下煤体卸围压强度、变形、声发射事件以及能量耗散演化特征,开展...     

Effect of CO2 on coal P-wave velocity under triaxial stressOA

As P-wave velocity is sensitive to the variations in coal reservoir parameters,it is possible to monitor the injected CO₂through P-wave velocity during CO₂sequestration in coal.However,the effects of CO₂on the coal P-wave velocity under triaxial stress are not clearly discerned.In the present study,different boundary conditions and gases were utilised to investigate the factors affecting the P-wave velocity after the interaction of coal with CO₂.Experi...     

Particle simulation of the failure process of brittle rock under triaxial compression

In order to investigate the failure process of brittle rock under triaxial compression through both experimental and numerical approaches, the particle simulation method was used in numerical simulations and the simulated results were compared with those of the experiment. The numerical simulation results, such as fracture propagation, microcrack distribution, stress-strain response, and damage patterns, were discussed in detail. The simulated results under various confining pressures (0-60 MPa) are in good...     

Stress-dilatancy of Zipingpu gravel in triaxial compression tests

Experimental investigations of the dilatancy and particle breakage of gravelly material from the Zipingpu concrete-faced rockfill dam, which was subjected to high-intensity seismic load during the 2008 Wenchuan earthquake, were conducted through a series of large-scale drained triaxial compression tests. A hyperbolic relation between the input plastic work and the degree of particle breakage was found for Zipingpu gravel, independent of the initial void ratio and confining pressures. The stress-dilatancy for Zipingpu gravel was analyzed and compared with data from two rounded alluvial and three angular quarried gravelly and rockfill materials in the literature. A nearly linear relationship between the dilatancy D~p and the stress ratio η was found at medium-to-large stress ratios before the peak stress ratio. The slope of the stress-dilatancy line before peak had slight dependence on the void ratio and confining pressure of the gravel. After peak, the stress-dilatancy relation shifts down compared with that before peak for the gravel specimen. The phase-transformation stress ratio decreased with increased confining pressure, with the exception of sub-rounded gravel with little particle breakage. A nearly linear relationship was found between the phase-transformation stress ratio M_f and the state parameter y for the Zipingpu gravel, regardless of the void ratio and confining pressure of the specimens.     

真三轴压缩下大理岩强度、变形与损伤特征数值

为研究真三轴条件下岩石的力学行为,采用离散元颗粒流程序,探析不同应力路径下大理岩试样的变形破坏过程、微裂纹演化机制及其中间主应力效应。结果表明：平行黏结模型能较准确地反映大理岩真三轴压缩下力学特性和破坏模式;中间主应力对峰值强度、弹性模量、破坏角和破坏模式演变的影响较为显著;八面体理论可较好地拟合出大理岩真三轴压缩中的破坏应力,所得的破坏强度包络线具有明显线性特征;结合应力-应变曲线形状,该大理岩在压缩过程中裂纹扩展可划分为4个阶段,即线弹性阶段、裂纹稳定扩展阶段、裂纹非稳定扩展阶段及峰后破坏阶段;随着中间主应力增大,应力-应变曲线峰后段的脆性破坏特征变强,试样从拉伸破坏向拉剪混合破坏转变,且中间主应变符号由拉转向压,岩石损伤演化与中间主应力间呈现出“对勾”型趋势。     

Acoustic emission characteristics and stress release rate of coal samples in different dynamic destruction time

Considering the importance of the prediction of rock burst disasters, and in order to grasp the law of acoustic emission(AE) of coal samples in different dynamic destruction time, the SH-II AE monitoring system was adopted to monitor the failure process of coal samples. The study of the change rule of the AE numbers, energy, ‘b' value and spectrum in the micro crack propagation process of the coal samples shows that as dynamic damage time went by, AE presented high-energy counts and the accumulated counts increased during the compression phase. The AE energy and cumulative counts increased during the elastic stage. The AE blank area increased gradually and the blank lines were more and more obvious in the molding stage. The AE counts and energy showed a trend of decrease in the residual damage phase.AE ‘b' values gradually became sparse, and the large scale cracks percentage compared with micro cracks decreased and the degree of damage decreased. The AE frequency spectrum peak went from the residual damage phase to the molding phase, and finally it was nearly stable, besides the bandwidth of the main frequency is gradually narrowed. Also, the frequency peak changed from single peak frequency to bi-peak frequency and to the single peak frequency. Uniaxial compressive strength is more sensitive than the elastic modulus to dynamic damage time.     

纤维混凝土三轴抗压强度及破坏特征的试验研究

利用伺服试验机对纤维混凝土和普通高强混凝土试样进行不同围压下轴向压缩试验,基于试验结果,研究了两种混凝土的单轴与三轴压缩强度,探讨了两种混凝土试样的破坏特征.结果表明,两种混凝土单轴压缩强度都达到80 MPa以上,普通高强混凝土单轴与三轴强度略高于与之配合比相同的混杂纤维混凝土;当围压达到20 MPa以上时,纤维混凝土峰值应力不显著,加载后期具有更大的塑性变形特征,说明掺入适量纤维可以提高混凝土的韧性,降低脆性;纤维混凝土试样加载结束后试样不断裂、不剥落,具有良好的整体性能.     

三轴受压状态混凝土当量损伤本构模型

本文根据Ｈ－Ｔ－Ｃｈｅｎ的多轴受压状态下的破坏准则,引用了混凝土损伤力学的概念,提出了在多轴受压状态下的当量损伤模型。可以模拟混凝土在多轴受压状态下的应力应变关系,得到等效单轴受压的应力应变全过程曲线,并且可求得在不同侧压力情况下混凝土的极限抗压强度。本模型不仅可模拟混凝土多轴受力的应力应变过程,并为拱坝非线性全过程分析了依据。     

声波团聚对燃煤电厂可吸入颗粒物的排放控制

为了从煤燃烧过程中脱除细粒子（PM_2.5）颗粒物以控制大气可吸入颗粒物（PM₁₀）的污染程度,将高强度的声场运用于气溶胶中以改变颗粒的粒径分布,使粒子团聚为较大的颗粒以在传统的除尘器中脱除.在1～5 kHz、110～140 dB行波声场内对燃煤电厂布袋除尘器收集的飞灰进行声团聚实验,载尘质量浓度为1～5 g/m3,并采用碰撞式分级仪和激光粒度仪MS-2000在线测量颗粒的粒度分布,得到声强和声波频率对团聚效果的影响.在1.72 kHz、140 dB声波团聚实验中,分级仪上的实验结果显示,PM_2.5减少52%～63.6%,PM₁₀减少35.6%～53.3%.     

焦作矿区含瓦斯煤体电阻率变化规律研究

在低频率（100～10000Hz）条件下测试了煤体在吸附瓦斯过程中和含瓦斯煤在三轴压缩条件下的电阻率变化规律．实验结果表明,煤体在吸附瓦斯过程中和含瓦斯煤三轴压缩条件下,电阻率值分别随着吸附时间和应力的增加,出现先大幅度减小后小幅度增大的变化规律．运用电介质物理学理论对含瓦斯煤体导电机理分析表明,电子和离于在煤孔隙表面上的迁移、游离瓦斯对煤颗粒的挤压作用和正负电荷在外电场作用下产生移动,三者共同造成煤体在吸附瓦斯过程和含瓦斯煤体受载过程中电阻率的降低．     

砂岩三轴常规压缩物理和数值实验分析

基于曹窑东井采空区砂岩试件的超声波测试实验,选出了岩性较好的试件,并在RMT-150 B岩石力学实验机上对砂岩试样在不同围压条件下进行常规三轴压缩物理实验;利用RFPA系统,研究了不同围压对岩石试样承载能力的影响.数值试验和物理实验表明,在较低围压条件下,试样的承载能力与围压大致成线性关系,即试样的承载能力随着围压的增高而增大.     

单轴压缩条件下不同裂纹制作方式的裂纹破坏分析及其声发射特征研究

采用类岩石材料研究了不同裂纹制作条件下张拉裂纹的破裂过程, 并利用声发射测试技术分析了试样在破坏过程中裂纹的萌生、起裂、扩展和破裂全过程的声发射特征。试验结果表明, 不同制作条件下裂纹扩张呈现不同的破坏方式,有不同的起裂强度和抗压强度,而且在hits t时间曲线上存在差别;声发射hits t时间曲线呈现与应力时间曲线同步性的特点,并且曲线自身突变性反映了裂纹扩展中能量释放的突发性,两者的符合性较好。     

阿刀亥煤矿掘进巷道煤壁瓦斯涌出规律的研究

针对阿刀亥煤矿1203炮掘巷道,通过现场实测掘进巷道煤壁瓦斯涌出量,建立了掘进巷道煤壁瓦斯涌出强度随时间的变化规律方程,确定出掘进巷道煤壁瓦斯涌出量与巷道长度、掘进速度及煤壁暴露时间的关系,给出了煤壁瓦斯涌出枯竭极限时间、掘进巷道煤壁最大瓦斯涌出量以及掘进巷道煤壁达到最大瓦斯涌出量时巷道长度的计算方法.该研究结果,对于指导矿井的通风设计和采掘部署,采取有针对性的防治煤巷掘进瓦斯灾害措施,具有重要的理论意义和实用价值.     

Electronic band Gap of ZnO under triaxial strain

The effect of triaxial strains on the band gap of wurtzite ZnO has been investigated by the first principles calculations. The results indicate that, after application of triaxial strain, the wurtzite ZnO is still a direct band gap semiconductor with conduction-and valence-band minima remains at the Γ point. Comparing with the unstrained ZnO, the Eg at Γ point increases under compressive strain but decreases under tensile strain. This triaxial strain model is in better agreement with the experimental results than the widely-employed in-plane biaxial strain model, thus providing a more accurate explanation on the behaviors of ZnO thin film under three-dimensional strain.     

孔隙压力作用下泥岩三轴蠕变实验研究

在具有孔隙压力系统的岩石三轴蠕变仪上,对泥岩进行了考虑孔隙压力作用的三轴蠕变实验.实验中不仅考虑了轴压σ₁和围压σ₃对蠕变的影响,而且考虑了孔隙压力p在泥岩蠕变过程中产生的重要影响.通过不同应力水平下的蠕变实验,对比含孔隙压力和不含孔隙压力的蠕变实验曲线,表明当轴压σ₁和围压σ₃一定时,随着孔隙压力p的增加,蠕变变形量将会减小,在稳态蠕变阶段的应变率也会减小,在一定程度上会延长蠕变三个阶段的蠕变时间.并采用经典蠕变模型对实验结果进行分析.