深部砂岩加卸载过程的能量演化分析

为了研究砂岩不同应力路径下的力学特征和能量演化规律,开展砂岩的三轴加载试验与同时卸轴压和围压的三轴卸荷试验.分析了在受荷破坏过程中围压以及应力路径对砂岩的力学特性以及能量演化规律的影响.结果表明:不同的应力路径下,围压增大可以提高试件的力学特性;不同应力路径下,围压的增高会提高峰值强度对应的总能量、弹性能以及耗散能;不...     

卸围压条件下花岗岩强度特性及三维裂隙演化规律

为研究卸围压条件下花岗岩强度特性和三维裂隙演化规律,对花岗岩开展了常规三轴压缩、卸围压-加轴压和分级卸围压-加轴压循环加卸载3种不同应力路径力学试验,获得对应的轴、径向应力-应变曲线;采用CT扫描三维重构技术获得岩石卸围压过程中和破坏后内部裂隙分布三维图像.结果表明:相对于常规三轴压缩试验,试件在卸荷条件下脆性破坏特征更加显著,分级卸围压-加轴压循环加卸载会增大花岗岩的峰后延性,降低破坏轴压和破坏剧烈程度;两种卸围压方案都会使花岗岩的承载能力降低30%左右;卸荷作用下花岗岩宏观破裂为拉剪组合状,拉剪过渡不明显,表观裂隙是内部裂隙向外扩展的结果;花岗岩在卸荷作用下峰前产生的裂隙量较少,大量裂隙在峰后产生,破裂具有突发性和瞬时性,围压较低时宏观裂隙首先在试件边缘产生,围压较高时宏观裂隙首先在试件中部产生.     

循环加载下单节理砂岩三轴强度与变形试验研究

为了研究节理砂岩试样在循环加载下的变形演化规律和强度特性,开展了贯通单节理砂岩在不同围压下的单调加载和循环加载试验.结果表明:随着围压的增加,节理砂岩试样单调及循环加载下峰值强度增大;在三轴循环加载作用下,节理砂岩的弹性模量的演化经历了明显增大、急剧减小、峰后趋于稳定3个阶段;三轴单调及循环加载下节理砂岩试样主要发生剪切破坏;在较低的围压(5,15 MPa)下,循环加载导致的破坏程度比单调荷载导致的更严重,在较高的围压(25,35 MPa)下,单调和循环加载下的破坏模式相似.     

载荷方式对深部采动煤体损伤-渗透时效特性影响实验研究

根据煤体实际力学状态设定恒定围压增加轴压、恒定轴压卸除围压和同时增加轴压卸除围压等3种力学路径,开展加卸载煤体损伤-渗透同步实验,分析加卸载方式对采动煤体损伤-渗透时效特性的影响,并揭示采动煤体损伤-渗透特性差异的内在机制.研究结果表明:不同的力学路径使煤体表现出截然不同的变形与强度特征,在高围压作用下试样的变形特性逐渐从脆性向塑性转变;受加卸载方式的影响,3种力学路径下的试样分别发生主剪切破坏、拉剪破坏和X型共轭剪切破坏;不同的力学路径对试样造成不同程度的损伤扩容和渗透率变化,且具有明显的时效特性,按响应速度排序依次是:同时增加轴压卸除围压恒定轴压卸除围压恒定围压增加轴压;煤体损伤、渗透具有协同演化特性,但渗透率变化相对于损伤扩容具有滞后性;差应力比是导致加卸载煤体损伤-渗透特性差异的本质原因,承受较大差应力比的深部采动煤体极易诱发煤岩瓦斯动力灾害,为避免动力灾害发生,需采取相应措施减小采动煤体所受的差应力比.研究结果对于揭示煤岩瓦斯动力灾害机理、实现深部煤炭精准开采与动力灾害防治具有指导作用.     

不同应力路径下超固结软黏土的永久变形特性

为了真实模拟软土路基在长期交通循环荷载作用下的沉降特性,通过部分排水条件下、不同应力路径下的正常固结及超固结温州饱和软黏土的循环三轴加载试验,对循环偏应力和循环围压耦合作用下饱和软黏土的永久轴向应变特性进行了研究,重点分析了超固结比及循环围压对饱和软黏土永久轴向应变的影响.研究结果表明:部分排水条件下,超固结土体相较于正常固结土体,其永久轴向应变提前趋于稳定,且稳定后的值随着超固结比的增大呈指数衰减;循环围压的存在可极大促进土体永久轴向应变发展,且循环偏应力和循环围压耦合作用对土体永久轴向应变的影响与超固结比无关.由此可见,在估算交通循环荷载下饱和软黏土产生的永久轴向应变时,对超固结比及循环围压的影响必须加以重视.     

多级循环荷载下饱和砾性土动三轴试验研究

为探究多级循环荷载下砾性土动力特性,以围压与动应力幅值为变量,开展了饱和砾性土动三轴试验,对轴向累积应变εd、回弹模量Ed、动孔隙水压力ud及滞回曲线的演化规律进行对比分析.研究结果表明:围压增加会促使砾性土Ed、ud增长,而使εd减小;随着动应力幅值的提高,Ed的发展趋势由随振次不断减小向逐渐增长转变;高动应力幅值(σd=150 kPa)下,ud均呈骤降→逐渐增大的变化趋势;在循环荷载下砾性土动应变主要是各阶段前期形变累积的结果,不同围压下各阶段前期(N≤1 500)动应变增量均占动应变总增量的90%左右;围压越大,土体的耗能作用越弱,刚度越大.     

循环荷载作用下非饱和击实粉土变形特性的试验研究

采用GDS非饱和土三轴仪,对循环荷载作用下的非饱和击实粉土样进行了控制吸力三轴排水剪切试验,研究了吸力、围压和动应力幅值对土样的变形特性的影响.试验结果表明:在相同动应力幅值和相同净围压下,吸力的增加提高了土体抵抗动变形的能力;在相同的净围压和吸力下,动应力幅值较小时,土样产生弹性变形且变形最终趋于稳定,动应力幅值较大时,经过一定的循环次数后土样达到破坏;净围压对试样的变形特性影响显著,围压较大时土样有较小的弹性变形,围压较小时土样发生明显的塑性变形.     

三轴循环加卸载下砂岩声发射分形特征试验

为探究砂岩在三轴循环加卸载条件下的声发射特性及其分形特征,对砂岩进行不同围压等级下常规三轴试验和三轴循环加卸载声发射试验,通过分析砂岩在三轴循环加卸载条件下峰前与峰后全过程的声发射特性及其分形特征,探究岩石渐进破坏过程中试样裂纹开展和损伤演化规律.采用MTS815 Flex Test GT岩石力学测试系统与PCI-Ⅱ型...     

膨胀土动力性质的研究

本文通过对静、动三轴试验的研究，探讨了重塑土在长期重复荷载下的动的应力─应交关系、动强度特性以及影响它们的主要因素，得到了累积塑性应变和循环次数的函数表达式以及临界动应力与围压、含水量等的关系，并同英国ＨｅａｔｈＤＬ的结果进行了对比．所得结果可供工程应用参考．     

真三轴条件下原状黄土的定量化结构性参数研究

为描述土的结构性及其变化引起的力学效果,基于综合结构势思想,结合真三轴仪对原状土和扰动饱和土(干密度一致)施加荷载,提出了一个能综合反映土颗粒排列和联结特征的定量化结构性指标,探讨了不同含水率、围压和中主应力条件下结构性参数在真三轴剪切过程中的变化特性。研究结果表明,该结构性参数在揭示含水率、围压和中主应力对真三轴剪切过程中土结构性的影响时表现出很好的灵敏性、合理性和稳定性。     

Mechanical property and permeability of raw coal containing methane under unloading confining pressure

Based on domestic-developed triaxial servo-controlled seepage equipment for thermal–hydrological–mechanical coupling of coal containing methane, an experimental study was carried out to investigate mechanical property and gas permeability of raw coal, under the situation of conventional triaxial compression and unloading confining pressure tests in different gas pressure conditions. Triaxial unloading confining pressure process was reducing confining pressure while increasing axial pressure. The research results show that, compared with the peak intensity of conventional triaxial loading, the ultimate strength of coal samples of triaxial unloading confining pressure was lower, deformation under loading was far less than unloading, dilation caused by unloading was more obvious than loading. The change trend of volumetric strain would embody change of gas permeability of coal, the permeability first reduced along with volumetric strain increase, and then raised with volume strain decrease, furthermore, the change trends of permeability of coal before and after destruction were different in the stage of decreasing volume strain due to the effect of gas pressure. When gas pressure was greater, the effective confining pressure was smaller, and the radial deformation produced by unloading was greater. When the unloading failed confining pressure difference was smaller, coal would be easier to get unstable failure.     

大理岩破坏起裂应力及断裂能特征试验研究

根据大理岩常规三轴试验数据,探讨不同围压下大理岩破坏的起裂应力和起裂断裂能变化规律.大理岩起裂应力位于峰值应力的53％～76％之间,随围压升高向峰值强度逐渐逼近.起裂断裂能与围压、峰值强度呈正线性关系.起裂应力对应的声发射能量计数率出现突跳,起裂点之后声发射能量计数率和累计释放能量增加速度明显变快,理论计算求得的起裂点和声发射监测数据吻合较好.大理岩常规三轴破坏符合Mogi-Coulomb强度准则.     

三轴加卸载下花岗岩脆性破坏及应力跌落规律

基于2种卸荷应力路径和常规三轴压缩试验,研究了加卸载条件下花岗岩的变形破坏及应力脆性跌落特征。卸荷条件下岩石变形主要是向卸荷（主）方向回弹或拉伸变形为主,而非或次卸荷方向的塑性变形很小,峰后应力应变曲线呈现明显的脆性特征。而加载条件下岩石以轴向压缩变形为主,且压缩塑性变形随围压增大而增大;卸荷条件下破坏岩石各种级别的张拉裂缝较多,张裂面一般垂直于卸荷主方向,高初始围压时双向卸荷甚至在次卸荷方向也可产生环形张拉裂缝。破坏围压较高时破裂面剪性特征相对明显,但剪性裂面一般追踪张性破裂面发展而成,并在剪切面两侧发育较多微张裂缝。而相对较高围压下常规三轴压缩岩石一般为剪切破坏,张性裂缝很少;常规三轴压缩岩石的应力脆性跌落系数随围压的增大而增大,而在卸荷条件下却随初始围压的增大而减小。相同初始围压时,卸荷条件下比加载时的应力脆性跌落系数小得多,方案Ⅱ在初始围压达到30 MPa时甚至出现负值,应力脆性跌落系数R依次为：RⅢ〉RⅠ〉RⅡ。     

岩石卸荷破坏的试验研究

对岩样进行了常规三轴加载后保持轴向变形不变的卸围压试验,得到了峰前、峰后卸围压全过程曲线。对岩样破坏特征和试验结果的分析表明:峰前卸围压岩样表现出脆性剪切破坏的特征,而峰后卸围压表现出张剪破坏的特征,峰前卸围压破坏比峰后卸围压破坏更具有突发性;峰前、峰后卸围压岩样都表现出明显的侧向扩容现象;岩样破坏时的轴向承载能力对围压都很敏感,反应了试件沿破裂面摩擦滑动的结构效应。     

Mechanical properties of deep-buried marble material under loading and unloading tests

The mechanical properties are essentially different when rock material is subjected to loading or unloading conditions. In this study, loading and unloading tests with various confining pressures are conducted to investigate the mechanical properties of marble material samples taken from the deep diversion tunnels of Jinping II Hydropower Station. The stress-strain relationship, failure characteristics and strength criterion are compared and analyzed based on the experiment results. The results show: in the loading and unloading test, peak strength, lateral strain, axial strain and plastic deformation increase significantly as the confining pressure increases. Lateral strain increased significantly and obvious lateral dilatancy can be observed to the change of confining pressure; The fracture mode is mainly the single shear fracture for the triaxial compression test and post-peak test, angle between the failure surface and the ends of the rock material becomes smaller as the confining pressure increases. Hoek-Brown strength criterion reflects the strength characteristics of marble material under two different unloading conditions, and has some supplementary effects to the rock material of mechanical field.     

Effects of confining pressure on acoustic emission and failure characteristics of sandstone

In this study, uniaxial and triaxial compression acoustic emission(AE) tests were implemented to investigate the AE effect and failure characteristics of sandstone under different confining pressures(σ_3). The evolution of AE parameters in the rock failure process and fracture fractal dimension characteristics after failure were analyzed. The results revealed that the activity of the AE signal is strongly related to σ_3. The evolution of the Ib value can be divided into the I-fluctuation, II-stability, and III-decrease stages. In the first stage, the Ib value of the AE was relatively high, and the AE energy was low. Then, the Ib value tended to be stable; however, the fluctuation amplitude decreased, and the AE energy rapidly increased. In the stage of decrease, the AE energy sharply increased before the load approached the peak value, and the Ib value significantly decreased and dropped to the lowest point before the peak value. As σ_3 increased, the rock's failure mode changed from tensile failure to shear failure and became more coordinated. As the confining pressure increased, the shape dimension decreased, and the order degree of rock failure increased. The confining pressure exerted a certain control effect on the rock failure.     

Space–time evolution rules of acoustic emission location of unloaded coal sample at different loading rates

By using MTS815 rock mechanics test system, a series of acoustic emission (AE) location experiments were performed under unloading confining pressure, increasing the axial stress. The AE space–time evolution regularities and energy releasing characteristics during deformation and failure process of coal of different loading rates are compared, the influence mechanism of loading rates on the microscopic crack evolution were studied, combining the AE characteristics and the macroscopic failure modes of the specimens, and the precursory characteristics of coal failure were also analyzed quantitatively. The results indicate that as the loading rate is higher, the AE activity and the main fracture will begin earlier. The destruction of coal body is mainly the function of shear strain at lower loading rate and tension strain at higher rate, and will transform from brittleness to ductility at critical velocities. When the deformation of the coal is mainly plasticity, the amplitude of the AE ringing counting rate increases largely and the AE energy curves appear an obvious “step”, which can be defined as the first failure precursor point. Statics of AE information shows that the strongest AE activity begins when the axial stress level was 92–98%, which can be defined as the other failure precursor point. As the loading rate is smaller, the coal more easily reaches the latter precursor point after the first one, so attention should be aroused to prevent dynamic disaster in coal mining when the AE activity reaches the first precursor point.     

超静孔隙水压下软土卸荷蠕变特性试验研究

考虑超静孔隙水压作用的软土卸荷力学特性对富水软土地区地下空间开挖变形和稳定性分析具有重要作用。以深圳地区淤泥质软土为研究对象,开展不同初始超静孔隙水压作用下的K₀固结不排水三轴卸荷强度试验和卸荷蠕变试验。试验结果表明：初始超静孔隙水压越大,固结围压越小,软土卸荷破坏越具有突然性;软土卸荷强度应力-应变曲线大致呈双曲线型,其双曲线函数拟合结果表明,卸荷强度随着初始超静孔隙水压的增大而大致线性减小。卸荷蠕变对初始超静孔隙水压敏感性很大,卸荷蠕变破坏时的偏应力约为卸荷强度试验中偏应力的90%。UU0.5应力路径相对于UU0.0应力路径更容易发生卸荷强度破坏和卸荷蠕变破坏,在实际工程中,应尽可能控制软土侧向卸荷比和超静孔隙水压的大小。     

Strength properties and evolution laws of cracked sandstone samples in re-loading tests

To study the strength properties and evolution laws of cracked sandstone samples in re-loading tests,strength and damage evolution properties of intact sandstone samples were first analyzed through the triaxial compression tests carried on TAW-2000 microcomputer control electro-hydraulic servo rock triaxial test system. Damage evolution models were established based on dilatancy properties realizing the real-time and quantitative evaluation of samples damage state in loading process. On this basis, samples with different damage were obtained by pre-peak, peak point, post-peak and residual strength stage unloading tests in the loading process of intact samples. The characteristics of the stress-strain curves and strength evolution laws were studied through the re-loading tests of samples with different damage under different stress states. The experimental results showed that the slope of stress-strain curves, peak strength and residual strength of cracked samples increased linearly with confining pressure and decreased linearly with damage. The equivalent cohesion decreased with damage in the exponential decay curves. The mechanics properties of samples transformed from strain softening to strain hardening with damage.