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.     

环向约束条件下破裂岩体力学特性试验研究

深部地下工程围岩多为破裂岩体，与支护结构间存在相互作用，破裂岩体的力学性能对工程稳定起着极其重要作用．采用环向约束试验方法研究破裂岩体的承载和变形特性．结果表明：破裂岩体的轴向应力-应变曲线是-分段连续曲线，峰谷后表现出等效弹塑性特性，随环向约束力的逐步提高，破裂岩体轴向应力呈现应力强化趋势，可达到并稳定在一个较高的应力状态，而环向约束应力则随侧向应变的增加呈线性增加，直至屈服．因此，环向约束条件下破裂岩体的力学特性明显不同于岩石三轴试验残余段的剪切滑移特性，反映了破裂岩体在有效环向约束条件下具有良好的结构效应．     

Mechanical properties and failure characteristics of fractured sandstone with grouting and anchorage简

Based on uniaxial compression experimental results on fractured sandstone with grouting and anchorage, we studied the strength and deformation properties, the failure model, crack formation and evolution laws of fractured sandstone under different conditions of anchorage. The experimental results show that the strength and elastic modulus of fractured sandstone with different fracture angles are significantly lower than those of intact sandstone. Compared with the fractured samples without anchorage, the peak strength, residual strength, peak and ultimate axial strain of fractured sandstone under different anchorage increase by 64.5–320.0%, 62.8–493.0%, and 31.6–181.4%, respectively. The number of bolts and degree of pre-stress has certain effects on the peak strength and failure model of fractured sandstone. The peak strength of fractured sandstone under different anchorage increases to some extent, and the failure model of fractured sandstone also transforms from tensile failure to tensile–shear mixed failure with the number of bolts. The pre-stress can restrain the formation and evolution process of tensile cracks, delay the failure process of fractured sandstone under anchorage and impel the transformation of failure model from brittle failure to plastic failure.     

饱和花岗岩水-力耦合力学特性试验研究

采用全应力多场耦合三轴试验仪,对饱和花岗岩开展了不同加载速率、不同围压、不同孔压下的水-力耦合三轴压缩排水试验,分别给出了饱和花岗岩在不同加载速率、不同有效围压下的应力-应变曲线,分析了峰值强度、峰值应变、弹性模量随加载速率以及有效围压的变化规律。研究结果表明:(1)在不同有效围压和加载速率的条件下,岩样的应力应变曲线均经历了非线性压密、弹性、屈服、峰后四个阶段。偏压加载初期非线性压密阶段比较明显,而随着围压的升高非线性段逐渐消失;由于花岗岩的致密性较高,因而曲线的弹性阶段较长且相对平滑;在屈服和峰后阶段,岩石呈现出明显的脆—延性转化的过程。(2)饱和花岗岩的峰值强度随着加载速率的增加而增大;且当有效围压相同时,岩石的峰值强度大致相等,抵抗外界荷载的能力大致相同。(3)缓慢加载条件下饱和花岗岩的峰值应变表现出加载速率强化效应,但强化效果是有限的;且在有效围压相同条件下,随着围压和孔压的同步增长,峰值应变也呈增长的趋势。(4)弹性模量随着加载速率的增加呈二次多项式增长,但随着围压和孔压的同步增长而逐渐降低。     

不同结构面倾角节理岩体三轴试验力学特性

为了掌握贯穿型节理岩体的变形和破坏规律,对人工制备的不同倾角模拟节理岩体圆柱试样进行了系列静力三轴试验,得到了相关的应力应变曲线结果和破坏特征,进而分析了结构面倾角对节理岩体试样力学特性的重要影响.结果表明:1)随着结构面倾角的变化,节理岩体试样的应力应变曲线将不全为典型的四阶段曲线,在结构面倾角较大时结构面的变形特征十分显著,峰前曲线发生了明显转折,结构面变形占据了主导作用.2)峰值强度、残余强度和峰前线性阶段变形模量随结构面倾角增大而单调降低,而试样的脆性和剪胀性强弱、压密阶段的变形模量以及体胀、体缩量最大值等与结构面倾角的变化关系则均为非单调的.3)结构面的倾角大小影响了其与基质的相互作用规律,使得结构面或基质或者两者一起控制了节理岩体试样的变形、强度和破坏,从而形成了节理岩体试样显著不同的变形、强度和破坏特征,其变形和强度各向异性与破坏模式随结构面倾角变化而不同.     

3D打印类岩石材料强度特性与动态损伤本构模型

为研究基于3D打印的层状类岩石材料动态损伤力学行为，对5组不同倾角的岩样，采用分离式霍普金森杆对其进行动态压缩试验。依据所得的应力-应变数据，以朱-王-唐本构模型为基础，建立一种线性弹簧体、Weibull分布损伤体和Maxwell体并联的黏弹性本构模型，并结合试样的残余强度特性引入损伤修正系数。最后，将其推广应用于黑色页岩的变形规律研究，以检验该本构模型的适用性。结果表明：动态冲击下岩样峰值应力随着倾角的增加呈现先减小后增大的“V”形变化趋势，与天然层状岩石的变化规律相符合；所构建的损伤本构模型，能准确地表征3D打印的层状类岩石材料的应力-应变曲线形状及其力学特征；考虑损伤修正后，其还可较好地反映试样峰后阶段应力应变变化特性与残余强度。研究结果对揭示层状岩石动载下变形规律具有一定参考价值。     

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.     

侧向卸荷条件下结构性软黏土典型力学特性

为研究海积结构性软黏土在侧向卸荷路径下的结构损伤特性,通过温州瑞安软黏土侧向卸荷条件下的应力路径试验,研究侧向卸荷路径和结构性对软黏土应力-应变关系、强度、初始卸荷模量等典型力学特性的影响;分析应力路径和土样深度对初始结构性及损伤特性的影响.试验结果表明:温州软黏土应力-应变关系呈明显应变软化型,具有较强的结构性;侧向卸荷条件下,初始切线模量与平均固结压力呈线性关系,斜率为加荷条件的1.4倍;侧向卸荷条件下达到峰值强度时对应的应变较常规加荷条件小.拓展了应力比结构性参数的应用范围,计算结果表明侧向卸荷条件下初始应力比结构性参数明显大于常规加荷条件.结构损伤曲线可分为平稳损伤、加速损伤和减速损伤三段,常规加荷条件下加速损伤段的损伤速率明显大于卸荷条件,这种差异与其各向异性有关,施工时需予以重点关注.     

不同冲击荷载下花岗岩力学和能量耗散特性

为探究不同冲击荷载条件下花岗岩的动力学特性,采用分离式霍普金森压杆分别对花岗岩试样进行单次和重复冲击荷载试验,并对试样的应力-应变响应、应变率曲线特征、能量耗散特性以及破坏形态进行综合分析.结果表明:单次冲击下,试样动态抗压强度与比能量呈现对数函数关系,试样破坏程度随着比能量的增加而逐渐增大；随着入射波峰值应力的增加,应力-应变曲线峰后段的回弹现象逐渐减弱,应变率曲线呈现出愈加明显的“双峰”特征,其第2波峰逐渐高于第1波峰.重复冲击作用下,当试样未破坏时,应力-应变曲线基本经历弹性加载、损伤演化和峰后回弹3个阶段,当试样经历最后一次冲击时,应力-应变曲线峰后段形状与试样的破坏程度有关.此外,试样破坏时的累积比能量越大,其破坏越严重,应变率曲线由“单峰”逐渐向“双峰”过渡.     

Behavior of High Performance PVA Fiber Reinforced Cement Composites in Triaxial Compression

Based on an extensive experimental program,the paper studies the behavior of HPFRCC under triaxial compression. The experimental parameters are lateral confining pressure and PVA fiber content by volume. The test results indicate that ultimate strength and peak strain are significantly improved with the increases of confining pressure. The confining effect introduced by the fibers becomes minor in triaxial compression tests,where there is relatively high external confining pressure. The axial stress-strain curves with different confining pressure and different PVA fiber content by volume are obtained. Lateral confining pressure constraints the lateral expansion of HPFRCC,so there is a big plastic deformation with its ultimate strength improved. At lower confining pressure,PVA fiber content by volume has some effect on the decreased section of stress-strain curve. According to test results,the paper establishes formula of confining pressure with ultimate strength and axial peak strain respectively.     

基于破坏类型的本溪灰岩本构关系研究

根据单轴和三轴条件下本溪灰岩的压缩试验和峰后循环加载试验,总结本溪灰岩的强度、变形随围压的变化规律,研究不同围压下本溪灰岩的破坏过程和重复加载过程,分析不同应力条件下本溪灰岩破坏的方式.结果表明:本溪灰岩在应力刚过峰值且未完全进入残余强度阶段,其弹性模量与峰前相同,此阶段进行循环加载时,新的峰值应力低于卸载点应力;在残余强度阶段,残余强度不再随重复加载发生明显变化;采用比较峰值时的环向弹性应变值与环向应变值的方法来判别本溪灰岩的破坏类型是可行的;不同围压下,本溪灰岩的破坏方式有张性破坏和剪切破坏2种类型,这2种破坏方式下本构模型的控制参数是不同的.分别选取了环向应变和剪切应变作为控制参数建立了本构模型,该模型很好地描述了本溪灰岩峰后阶段的应力脆性跌落现象及应力与应变的关系.     

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。     

Hardfill筑坝材料应力—应变特性与本构模型研究

胶凝砂砾石（Hardfill）材料是用少量胶凝材料将砂砾料固结得到的一种低强度筑坝新材料。通过对材料试验资料的分析,获得Hardfill材料应力—应变关系的特点为：表现出较典型的弹塑性材料应力—应变特征;在低应力水平表现为线弹性性质,当应力达到峰值强度的60%～80%后逐步进入弹塑性阶段,直至达到峰值强度;其后,应力随...     

水影响下油页岩三轴压缩力学特性试验研究

为研究油页岩的力学特性,试验采用吉林桦甸油页岩试样,利用YE-200A液压式压力试验机和自制三轴压力室,进行油页岩三轴压缩实验。通过不同围压、不同水化时间的三轴压缩实验,揭示油页岩全应力-应变、峰值强度、弹性模量、泊松比随不同围压和水化时间的变化规律,以及油页岩的破坏形式。结果表明,水化对油页岩的力学特性影响很大,使其峰值强度和弹性模量降低,同时,还表现出明显的延性效应;另外,围压和水化作用的对比分析表明,在围压影响下水化对油页岩强度影响比自然状态下小,油页岩因原岩裂隙发育不同水化后呈现不同的破坏形式。     

冻融损伤混凝土重复受压本构关系

为研究冻融损伤对混凝土重复受压力学性能的影响,完成了两种强度等级混凝土试块的快速冻融及重复受压试验.结果表明,冻融损伤混凝土重复受压力学性能显著降低,动力本构特征曲线也发生改变,包络线及再加载曲线在峰值应力之前因存在明显压实效应而表现出下凹形态,卸载曲线应变滞后现象严重且曲线逐渐趋于重合.在试验研究基础上,探讨了冻融循环次数、混凝土强度等级与冻融后混凝土力学性能参数及本构模型参数之间的关系,建立了冻融损伤混凝土动力本构模型.     

Relations of complete creep processes and triaxial stress-strain curves of rock

Based on the results of triaxial compressive creep tests for five kinds of rock under the different stress loading,unloading and cycle-loading-unloading conditions,the creep deformation is not only a function of stress and time,but also it has the corresponding relations to the triaxial stress-strain curves of rock.The deformation properties of soften-strain,harden-strain and ideal plasticity presented by conventional triaxial compressive test curves under the different stress states were utilized,and the creep characteristics,the creep starting stress and the different entire creep process curves of rock were studied systematically according to creep experiment results,and the relations of the triaxial stress-strain curves to the creeping starting stress,the terminating curve,the different creep processes,and the different creep fracture properties were established.The relations presented in this paper were verified partially by the creep experiment results of five types of rock.     

深部重塑土高压应力路径试验研究

为了获取高压条件下应力路径对深部土力学特性的影响,采用自行设计的室内高压试验方法研究了深部重塑土在K_0固结基础上4种典型应力路径下的应力-应变行为和强度特性.结果表明:三轴压缩路径下的应力-应变曲线形态呈应变软化型,三轴拉伸路径下的应力-应变曲线则由线性段和应变硬化段组成;三轴压缩路径下深部重塑土的屈服强度和屈服变形均大于三轴拉伸路径,而抵抗破坏的能力刚好相反,且加荷条件下深部土抵抗破坏的能力高于卸荷条件.深部重塑土的室内高压试验应根据工程实际选取合理路径以避免重大事故的发生.     

不同围压下灰岩力学特性及破坏力学模型研究

为了研究围压对灰岩力学特性及破坏力学模型的影响,采用MTS815对完整灰岩岩样进行三轴压缩试验。基于岩样宏观破坏形式,建立张拉剪切破坏模型,构建峰值强度与围压关系表达式;讨论张拉剪切模型与纯剪切模型对岩石剪切强度参数值（粘聚力与内摩擦角）的影响。研究结果表明：岩样弹性模量、抗压强度及残余强度均随围压升高而增大,且残余强度与围压呈非线性相关;当岩样最终破坏时,环向应变与轴向应变比值随围压升高呈负指数降低;一定围压范围内,岩石抗压强度受剪切强度参数和抗拉强度影响;张拉剪切模型确定岩石剪切强度参数值随破裂角增大而增大,与纯剪切模型相比,数值均较小。因此,低围压时,考虑岩石破坏模型具有一定的实际意义。     

初始各向异性对软土强度与变形的影响试验研究

通过压缩试验、无侧限抗压强度试验以及三轴固结不排水试验,对海积软土初始各向异性影响土体强度与变形进行了试验研究.结果表明:在一维压缩试验中,海积软土垂直方向的压缩变形最小,水平方向的变形最大,而45°斜方向的变形介于两者之间;在三轴压缩试验中,海积软土的应力-应变关系都呈现应变硬化,垂直方向的峰值强度最强,45°斜方向最弱,水平方向的强度介于两者之间.在此基础上,对其进行了机理分析,研究成果对工程实践有一定的指导意义.     

含水率对花岗岩残积土邓肯-张模型参数影响

制作了不同含水率花岗岩残积土击实试样,进行一系列固结排水三轴试验.得出在不同围压和不同含水率条件下,花岗岩残积土击实试样在三向应力作用下均呈现鼓胀破坏的变形特征,其固结排水应力-应变曲线均为加工硬化型,与邓肯-张模型的条件式基本吻合.通过邓肯-张模型参数的计算与分析,得知含水率对花岗岩残积土的邓肯-张模型参数整体上影响较大,其中粘聚力受影响最显著,无因次指数n和低围压时的初始变形模量受影响较显著,基本规律为:抗剪强度指标粘聚力、内摩擦角值,初始变形模量及无因次基数K均随着含水率的增大而减小;无因次指数、破坏比随含水率的增大而增大;各参数与含水率关系曲线均在最优含水率处出现拐点,且当含水率大于最优含水率时,其对各参数的影响不同程度地加大.