不同频率循环荷载下大理岩动力学特性试验研究

利用MTS 815岩石力学试验系统,对大理岩进行了单轴压缩和不同振动频率、不同动应力幅值的循环加卸载试验,探讨循环荷载的振动频率和动应力幅值对大理岩的动弹性模量和动泊松比的影响.研究结果表明,在不同应力幅值的循环荷载作用下,大理岩的动应力-动应变曲线不完全重合,形成了滞回环;随着动应力级别的提高,滞回环面积增大,能量耗散增加;随着循环周次的增加,累积不可逆变形增大.当动应力幅值的范围分别处在岩石弹性变形阶段和塑性变形阶段时,振动频率和动应力幅值对动弹性模量和动泊松比的影响不同.随着循环应力级别的提高,动弹性模量减小,而动泊松比呈现出逐渐增加的趋势;当动应力幅值处在岩石的屈服点以上时,随着振动频率的增大,动泊松比增加、动弹性模量减小.     

弯曲加卸载下杂质盐岩断裂力学行为特征研究

为研究弯曲荷载下杂质盐岩断裂力学行为及损伤演化规律,利用四川大学MTS815岩石力学测试设备及三维声发射监测系统,展开了纯盐岩、含杂卤石盐岩及杂质盐岩三点弯曲加卸载试验。试验结果表明：(1)杂卤石及泥质胶结提升了盐岩的韧性,纯盐岩的断裂韧度均值KIC=6.36MPa.mm^-0.5,杂卤石盐岩的断裂韧度较纯盐岩高43.08%,杂质盐岩的断裂韧度为纯盐岩的3.18倍;(2)杂质导致盐岩脆性提高,纯盐岩声发射事件覆盖区域大于杂卤石盐岩及杂质盐岩;三点弯曲加卸载下岩石内部声发射事件由切槽尖端逐渐向荷载点扩散,直至岩石完全断裂;(3)盐岩损伤程度随循环次数增长逐渐提高,但增长速度逐渐降低,损伤变量与切槽张开度符合指数函数关系,损伤变量-张开度曲线拐点对于研究岩石失稳倾向性具有一定的预测效果;(4)声发射参数rc值能够反映盐岩弯曲加卸载破坏全过程中主裂纹与微裂纹的发展趋势,峰后残余阶段纯盐岩及杂卤石盐岩rc曲线持续上升,微裂隙稳定发展;杂质盐岩表现出更强的脆性,其在峰后残余阶段rc曲线表现出与纯盐岩及杂卤石盐岩相反的变化趋势。     

单轴分级循环加载条件下砂岩疲劳变形特性与损伤模型研究

利用MTS815电液伺服试验机对两组砂岩试样进行了单轴分级循环加卸载试验,分析了分级循环加卸载应力-应变曲线特征和分级循环加卸载下岩石疲劳损伤演化过程,建立了循环加卸载条件下轴向应变与循环数目之间的理论模型,并推导了评价岩石损伤程度的损伤变量演化方程.结果表明:理论模型可以作为岩石循环加卸载条件下的破坏准则,试验结果与理论值之间相关度超过98%,同时,其逆函数可以实现对岩石疲劳寿命的预测;疲劳损伤演化方程可以衡量循环加卸载过程中疲劳损伤的发展水平;疲劳循环上限应力值是决定岩石疲劳寿命的关键因素,随着上限应力的提高,岩石的疲劳寿命呈现几何级数下降.     

岩石应力敏感曲线机制分析

根据固体力学的有关知识,研究了岩石应力敏感曲线测试过程中的机理问题.岩芯应力敏感曲线测试时因封套的塑性变形,使得加载曲线与卸载曲线产生了较大的差异,也夸大了岩石的应力敏感程度.实际上,应力敏感测试时,岩芯只产生弹性变形,而不产生塑性变形.加载时封套有塑性变形,卸载时封套和岩芯都无塑性变形.卸载曲线的应力敏感程度,包含了封套的弹性变形部分.扣除封套的变形因素,岩石自身的应力敏感程度极其微弱.     

节理砂岩在循环加卸载下力学特性及损伤规律实验研究

为研究不同方向频繁扰动对节理岩体力学特性及损伤规律的影响,利用伺服试验机对南坡铜矿砂岩平行层理方向、垂直层理方向进行单轴循环加卸载,每次应力水平依次递增的实验,直至岩石破坏,通过实验数据分析得到:1平行层理方向加载的泊松比和弹性模量比垂直层理方向大,破坏强度相反;2卸载阶段的弹性模量和泊松比总比对应的加载阶段的要大;3随着循环次数的增加,两种加载方向均体现出形成的封闭塑性滞回环的面积逐渐增大,但垂直层理方向增加幅度要明显大于平行层理方向;且对应的各循环阶段的滞回环面积比平行层理方向要大;4每次循环残余变形量总比上一次的要大,但增长速度降低,降低幅度为5%~10%;5对于两种不同的加载方向,损伤规律、纵向应变的发展及应力大小有很好的一一对应关系,且岩石的损伤记忆性不受各向异性影响.     

层状盐穴储库中盐岩和泥岩蠕变特性试验研究

针对层状盐穴储气库中不同岩性之间变形不协调问题,本文利用四川大学大型程控流变仪对盐岩和含盐泥岩两种岩石进行了常规单轴加载和单轴多级加载的蠕变的对比试验研究,重点探讨了两者蠕变力学特性之间的异同。研究结果表明：盐岩的塑性变形能力、流变特性明显强于含盐泥岩,因加载应力产生的瞬时应变量均呈先减小后增大的趋势,与常规单轴下张拉破坏不同,长期蠕变试验条件下,两者均以张剪型破坏为主;同等应力百分比情况下,盐岩的稳态蠕变率明显高于含盐泥岩,稳态蠕变率随着加载应力的增加而增大,并呈指数型函数变化,盐岩对应力的敏感性明显强于含盐泥岩;利用等时应力-应变曲线拐点法对两种岩石的长期强度值进行分析,得到盐岩的长期强度值为12MPa,为短期抗压强度的48%,含盐泥岩的长期强度值为34~36MPa,较短期抗压强度下降约30%,盐岩的长期强度值与短期抗压强度的比值远低于大多数岩石的比值。     

岩石动静态参数间关系的研究

岩石由矿物颗粒组成,内部存在弱面、裂隙等结构,并非线弹性材料,动静态参数之间并没有确定的力学关系.含有大量裂隙的砂岩、煤等软弱岩石,动态模量大于平均模量;大理岩的动态模量大于变形模量,但与平均模量的关系较为复杂;火成岩及其变质岩,动态模量可以小于变形模量.动态泊松比对波速极端敏感,与静态参数没有明确的关系.现场取回岩块已经卸载、脱水,岩样加工也会对材料产生损伤,内部出现张开裂隙,超声波速度降低.如某大理岩矿岩墙端头所测纵波速度的平均值就大于室内岩样纵波速度的最大值,因而以岩体与岩样纵波速度的比值评价岩体完整性将偏于不安全.     

岩石动静态参数间关系的研究

岩石由矿物颗粒组成,内部存在弱面、裂隙等结构,并非线弹性材料,动静态参数之间并没有确定的力学关系.含有大量裂隙的砂岩、煤等软弱岩石,动态模量大于平均模量;大理岩的动态模量大于变形模量,但与平均模量的关系较为复杂;火成岩及其变质岩,动态模量可以小于变形模量.动态泊松比对波速极端敏感,与静态参数没有明确的关系.现场取回岩块已经卸载、脱水,岩样加工也会对材料产生损伤,内部出现张开裂隙,超声波速度降低.如某大理岩矿岩墙端头所测纵波速度的平均值就大于室内岩样纵波速度的最大值,因而以岩体与岩样纵波速度的比值评价岩体完整性将偏于不安全.     

考虑加卸载时长的路基土动态回弹模量测试方法及试验研究

路基土动态回弹模量是沥青路面结构设计中的重要参数,准确获取路基土动态回弹模量一直是道路工程领域的重要研究课题之一。在调研路基土动态回弹模量测试方法相关成果的基础上,通过有限元数值计算、试探性试验,建立考虑行车荷载加卸载时长影响的路基土动态回弹模量测试方法;选取两种典型的路基土,开展考虑行车荷载加卸载时长的动态回弹模量试验。试验结果表明：两种土质动态回弹模量随围压增大而增大,随循环偏应力、加载时长的增大而减小;随着加载时长的增加,路基土动态回弹模量减小可达34.6%,加载时长的影响不容忽视;不同加载时长下,路基土动态回弹模量随围压、循环偏应力的影响规律基本一致。     

覆岩不同采动损伤煤样应力敏感性研究

为了研究覆岩不同采动损伤程度煤样渗透率的应力敏感性,基于覆岩各分带内煤岩损伤裂隙发育情况,将煤体分为弹性煤样(弯曲下沉带)、贯穿裂隙煤样(裂隙带)以及破碎煤样(垮落带).结合不同损伤程度煤样循环加卸载实验拟合参数,提出绝对应力敏感性系数及相对应力敏感性系数评价各类煤样重复加卸载过程中的应力敏感性大小及变化趋势.研究结果表明:第1次加载阶段的绝对应力敏感性远大于之后的加载阶段.在应力加载初期,贯穿裂隙煤样的绝对应力敏感性系数大于破碎煤样且远大于弹性煤样,而弹性煤样的相对应力敏感性系数大于破碎煤样与贯穿裂隙煤样;在应力加载后期,破碎煤样的绝对与相对应力敏感性系数均大于贯穿裂隙煤样及弹性煤样.     

Strength and elastic properties of sandstone under different testing conditions

A laboratory experimental program performed on Wuhan sandstones was presented under monotonic loading, partial cyclic loading during loading path and sine wave cyclic loading with different strain rates to compare uniaxial compression strength and elastic properties （elastic modulus and Poisson ratio） under different conditions and influence of pore fluid on them. When the loading strain rates are 10^-5, 10^-4 and 10^-3/s, uniaxial compression strengths of dry sandstones are 82.3, 126.6 and 141.6 MPa, respectively, and that of water saturated sandstones are 70.5, 108.3 and 124.1 MPa, respectively. The above results show that the uniaxial compression strength increases with the increase of strain rate, however, variation of softening coefficient is insignificant. Under monotonic loading condition, tangent modulus increases with an increment of stress （strain） to a maximum value at a certain stress level, beyond which it starts to decline. Under the partial cyclic loading during loading path condition, unloading or reloading modulus is larger than loading modulus, and unloading and reloading moduli are almost constants with respect to stress level, especially unloading modulus. Under the sine wave cyclic loading condition, tangent modulus and Poisson ratio display asymmetric ‘X＇ shape with various strain, and the average unloading modulus is larger than the average loading modulus.     

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.     

循环荷载下考虑滞回效应的混凝土损伤模型

针对高混凝土坝地震过程中复杂的材料非线性问题,建立循环荷载下考虑滞回效应的混凝土损伤模型。模型分别选取符合混凝土实际变形特性的拉伸与压缩骨架线以考虑材料拉压异性,骨架线中含有软化段系数以适应试验结果的离散性。采用不依赖于骨架线形状的滞回效应加卸载特征点表达式,搭建能够反映混凝土循环荷载作用下软化段滞回效应的卸载路径与重新加载路径,并建议设立残余应变临界值解决残余塑性应变与卸载应变比值随应变增长的持续发散问题。模型将复杂多轴问题转化至单轴等效应变空间中求解,计算参数少,数学表达式简单,并通过混凝土循环荷载试验与Koyna重力坝的震害模拟验证了模型在非线性问题求解上的正确性与高效性。     

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.     

花岗岩和大理岩在不同应变率下的冲击试验研究

利用橡胶波形整形器改进后的分离式霍普金森压杆装置,对花岗岩和大理岩在不同应变率下进行了冲击压缩试验。通过试验有效性的验证,证明了数据的可靠性。试验结果表明:应变率明显影响这两类岩石材料的动态力学特性,不同冲击速度下的动态抗压强度、峰值应力、弹性模量表现出显著的率相关性,峰值应变则变化不大,其中分析了花岗岩和大理岩的峰值应力-冲击速度关系以及弹性模量-冲击速度关系,两者呈弱幂函数关系;加载过程中花岗岩表现出更显著的动态脆性,在破坏形态方面花岗岩大多呈轴向劈裂破坏,大理岩破碎程度明显更高呈压碎破坏,并从微观结构方面进行了对比分析。     

Cyclic constitutive equations of rock with coupled damage induced by compaction and cracking

In this paper, the cyclic constitutive equations were proposed to describe the constitutive behavior of cyclic loading and unloading. Firstly, a coupled damage variable was derived, which contains two parts, i.e., the compaction-induced damage and the cracking-induced damage. The compaction-induced damage variable was derived from a nonlinear stress–strain relation of the initial compaction stage, and the cracking-induced damage variable was established based on the statistical damage theory. Secondly, based on the total damage variable, a damage constitutive equation was proposed to describe the constitutive relation of rock under the monotonic uniaxial compression conditions, whereafter, the application of this model is extended to cyclic loading and unloading conditions. To validate the proposed monotonic and cyclic constitutive equations, a series of mechanical tests for marble specimens were carried out, which contained the monotonic uniaxial compression (MUC) experiment, cyclic uniaxial compression experiments under the variable amplitude (CUC-VA) and constant amplitude (CUC-CA) conditions. The results show that the proposed total damage variable comprehensively reflects the damage evolution characteristic, i.e., the damage variable firstly decreases, then increases no matter under the conditions of MUC, CUC-VA or CUC-CA. Then a reasonable consistency is observed between the experimental and theoretical curves. The proposed cyclic constitutive equations can simulate the whole cyclic loading and unloading behaviors, such as the initial compaction, the strain hardening and the strain softening. Furthermore, the shapes of the theoretical curves are controlled by the modified coefficient, compaction sensitivity coefficient and two Weibull distributed parameters.     

单轴加卸载条件下岩盐变形过程能量和声发射特征研究 （研究生论坛）

利用 MTS815 Flex Test GT 岩石力学试验系统及声发射(AE)实时监测系统,对取自平顶山和淮安两处矿井的纯盐岩进行了单抽加卸载试验,得到了岩盐的应力-应变加卸载曲线、声发射振铃计数率和能量率曲线,并且从能量与声发射的角度研究了纯岩盐变形破坏过程的基本特征。通过研究表明,岩盐单轴加卸载条件下,弹性变形阶段很短,屈服过程产生很大的塑形变形,且峰后的变形过程没有应力的急剧下降,整个实验过程中加卸、载之间滞回环面积很微小。在整个实验过程中,弹性应变能占的比例非常的小;盐岩单轴加卸载变形破坏过程中,其耗散能随应变一直增加,且增长率递增,而当应力接近峰值时,增长率趋于恒定,耗散能曲线开始呈线性增长;弹性应变能在峰前一直增加,且增长率递减,在峰值处达到最大值,峰后开始下降。岩盐在试验初始阶段振铃计数率与能量率便大量产生,而后在屈服阶段呈现下降进入稳定发展期,直到峰值处,出现一个累计振铃计数和累计能量曲线的拐点,峰后以一个更高的速率稳定地且呈现阶梯状发展。本文对于盐岩储气库的水溶开挖和采气过程中逐渐卸载的应力环境施工过程有一定的实际指导意义。     

卸围压条件下砂岩变形破坏特性试验研究

从可释放弹性应变能角度对岩石卸围压条件下破坏特性进行研究,利用MTS815电液压伺服可控制刚性试验机进行保持轴向变形不变的卸围压试验,根据卸围压试验数据,分析了该砂岩卸围压过程中变形、强度、弹性模量及能量变化特征。结果表明:随着围压逐渐降低,岩样发生侧向不断扩容;轴向应力逐渐降低,呈现出非线性特征;弹性模量在初始阶段几乎不变化,越过破坏点之后大幅降低;可释放的弹性应变能在初始阶段增大比较缓慢,当围压降低至一定程度时急剧增大;推导出基于可释放弹性应变能的卸荷岩石的整体破坏准则Ue0。     

Viscous property of dried clay

One dimensional and triaxial compression tests of air-dried and oven-dried Fujinomori clay and Pisa clay were carried out. Water content is less than 4.5% and 1.0% for air-dried and oven-dried clay specimens, respectively. In all tests, axial strain rate was changed stepwise many times and drained creep tests were performed several times during monotonic loading at a constant strain rate. Global unloading （and also reloading in some tests） was applied during which creep loading tests were performed several times. Cyclic loading with small stress amplitude and several cycles was also performed to calculate the modulus of elasticity of the clay in tests. Local displacement transducer was used in triaxial compression test to increase measuring accuracy of axial strain. The results show that air-dried and oven-dried clay have noticeable viscous properties; during global unloading, creep deformation changes from positive to negative, i.e. there exist neutral points （zero creep deformation or no creep deformation point） in global unloading part of strain-stress curve; viscous property of Fujinomori clay decreases when water content decreases, i.e. viscous property of air-dried Fujinomori clay is more significant than that of oven-dried Fujinomori clay.