Experimental research on creep behaviors of sandstone under uniaxial compressive and tensile stresses

The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the self-developed direct tension device and creep testing machine RLW-2000M are used to conduct the creep tests on red sandstone under uniaxial compressive and tensile stresses. The short-term and long-term creep behaviors of rocks under compressive and tensile stresses are investigated, as well as the long-term strength of rocks. It is shown that, under low-stress levels, the creep curve of sandstone consists of decay and steady creep stages; while under high-stress levels, it presents the accelerated creep stage and creep fracture presents characteristics of brittle materials. The relationship between tensile stress and time under uniaxial tension is also put forward. Finally, a nonlinear viscoelastoplastic creep model is used to describe the creep behaviors of rocks under uniaxial compressive and tensile stresses.     

Experimental investigation of the mechanical behaviors and energy evolution characteristics of red sandstone specimens with holes under uniaxial compression

Bulletin of Engineering Geology and the Environment - To explore the mechanical behaviors and energy evolution characteristics of rock materials with hole defects, eight types of red sandstone...     

高温后再生砂浆单轴受压应力-应变关系试验研究

为得到高温后再生砂浆单轴受压应力-应变关系,对72个70.7 mm×70.7 mm×216 mm不同再生细骨料取代率的再生砂浆试件进行单轴受压试验,实测了20~800℃温度作用后试件的应力-应变全曲线,分析了再生砂浆的高温性能,以及再生细骨料取代率和经历温度对再生砂浆峰值应力、峰值应变、弹性模量、泊松比、体积应变和单轴受压应力-应变全曲线的影响。结果表明:不同再生细骨料取代率的砂浆试件高温后的表面颜色均经历灰色、浅红、灰白的过程,温度高于400℃以后开始出现裂缝、掉皮、疏松等现象;再生砂浆试件高温后质量损失率高于普通砂浆试件,温度高于400℃以后各类砂浆试件的质量损失率保持稳定;相同温度下,随着再生细骨料取代率的增加,单轴受压应力-应变曲线峰值应力减小,峰值应变增加,弹性模量减小,脆性更加显著;随着温度的升高,峰值应变逐渐增大,而峰值应力、弹性模量与体积应变临界点对应的应力比均持续减小,应力-应变曲线渐趋扁平。通过回归分析,建立了再生砂浆高温后峰值应力、峰值应变、弹性模量与温度的关系计算式,以及单轴受压分段式本构方程。     

高温后再生混凝土单轴受压应力-应变关系试验研究

利用废弃混凝土经机械破碎后制成的再生粗、细骨料,制作168个不同再生粗、细骨料取代率尺寸为100mm×100mm×300mm的再生混凝土试件,经历20～800℃作用后进行单轴受压应力-应变全曲线试验,分析了不同再生粗、细骨料取代情况和经历温度对再生混凝土峰值应力、峰值应变、弹性模量、泊松比和单轴受压应力-应变全曲线的影响。结果表明：相同温度作用后,随着不同再生骨料取代率的增加,峰值应变增大,弹性模量减小,单轴受压应力-应变曲线峰值应力减小,峰值应变增大,脆性增大;随着经历温度的升高,峰值应变与泊松比先降后增,并在温度400℃后增幅最大,而峰值应力与弹性模量均持续减小,应力-应变曲线渐趋扁平,与横轴包围面积显著减小;再生粗、细骨料单独掺入对混凝土受力性能的影响比较一致,同时掺入时性能退化较快。通过回归分析,建立各组再生混凝土试件单轴受压分段式应力-应变本构方程。     

单轴压缩下填充含缺陷砂岩力学性能试验研究

通过单轴压缩试验,对含孔洞砂岩岩样及充填含孔洞砂岩岩样进行了研究,并从裂纹扩展角度,阐释了填充含缺陷砂岩力学性能的变化规律,得出了一些有意义的结论,为同类问题的研究提供了依据。     

高温后砂岩单轴压缩加载速率效应的试验研究

温度是影响岩石材料物理力学性质的重要因素,为考察温度对砂岩加载速率效应的影响规律,对25℃～800℃之间6种温度水平后的砂岩试样分别进行不同加载速率下的单轴压缩试验。试验结果表明：① 高温后砂岩的物理性质出现一定的劣化,由25℃升高至800℃,密度和纵波波速分别减小了5.89%和73.72%;② 随着温度的升高,砂岩峰值强度和弹性模量逐渐减小,峰值应变逐渐增大,而峰值强度随温度的变化过程受加载速率的影响较大;③ 高温后砂岩的峰值强度和峰值应变具有明显的加载速率效应,且服从正线性关系,相关性参数A表征了材料受加载速率影响的显著程度,随着温度的升高参数A呈现先减小后又增大的趋势;④随着温度和加载速率的增大,砂岩破坏形态由拉剪混合破坏逐步转化为单一斜剪破坏,破坏程度愈渐剧烈,分形维数也逐渐增大。     

单轴压缩砂岩细观裂纹动态演化特征试验研究

岩石细观裂纹的动态演化特征作为岩石破坏的重要信息,其研究对于分析岩爆的孕育过程及预测岩石动力灾害发生有着重要意义。采用应力分析和声发射参数方法,研究了砂岩在单轴压缩条件下的细观裂纹的强度动态演化特征。试验结果表明,应力与砂岩细观裂纹扩展诱发声发射（AE）事件的强度特征有较好的阶段性变化规律,将峰前裂纹动态演化划分为三个阶段。进一步分析裂纹的类型特征,提出三阶段四维演化过程分析方法。细观裂纹多为张拉型,随着时间的增加,细观裂纹向剪切型裂纹转变,裂纹数量迅速增加,裂纹强度逐渐增大。提出将第三阶段AE事件出现的高强度、高RA、低AF特征作为砂岩破裂失稳的定性预警条件。通过矩张量反演对比分析了的细观裂纹数量和类型的动态演化。     

Study on the effect of axial and hydraulic pressure coupling on the creep behaviors of sandstone under multi-loading

Bulletin of Engineering Geology and the Environment - The pressurized water-rock coupling has a great influence on the long-term stability of rock engineering. In order to study the effect of axial...     

早龄混凝土的压缩与拉伸徐变及其研究现状

早龄混凝土的拉伸、压缩徐变规律及其结构徐变应力计算方法是对早期裂缝进行有效预测并控制的关键。既有的徐变研究主要侧重于成熟混凝土,而早龄混凝土徐变相关的科学研究还有待进一步深入。对早龄混凝土的压缩和拉伸徐变研究成果、测试方法及其徐变应力计算方法进行了详细综述。研究表明:目前混凝土早龄期拉伸、压缩徐变试验测试尚无规范可循,相关试验数据较为缺乏;混凝土早龄期徐变预测模型基本未考虑其在低应力水平下的非线性性质;早龄混凝土结构非线性徐变应力理论分析方法亦不尽完善。基于系统试验研究和固化徐变理论建立混凝土非线性徐变理论模型,对早龄混凝土结构采用同时考虑受拉和受压不同应力松弛特性的非线性徐变应力理论计算方法,应可提高早龄结构的有限元仿真精度。     

无纺织物单向拉伸孔径变化试验与理论预测对比分析

无纺织物作为反滤材料,常处于单向受拉工作状态。单向拉伸引起无纺织物孔径变化,易导致反滤工程失效。通过控制织物应变的干筛试验,定量测试了无侧限单向拉应变逐级增大的过程中,两种不同厚度短纤针刺无纺织物的孔径分布曲线变化。采用干筛试验结果,对现有两种体系的单向应变下无纺织物孔径预测理论解进行验证:一类是佘巍等效孔径O95理论解,一类是Rawal孔径分布曲线理论解。通过对比两种理论解对各级拉应变下的O95值预测,归纳二者的预测误差规律,从理论假设出发分析误差原因。同时采用前人图像法测得的热粘无纺织物O95变化验证两类理论解。两种理论解均能较好地预测无侧限单向拉应变下无纺织物O95的变化规律。O95随单向拉应变呈近似线性减小的规律。对于O95变化斜率的预测,佘巍解较准确,Rawal解偏大。对于O95数值预测可结合两类理论解给出变化范围。     

单向拉伸荷载下堆焊成型套筒灌浆连接性能试验研究

为研究套筒灌浆连接的力学性能、工作机理以及套筒内腔构造参数对其力学性能的影响规律,采用堆焊成型套筒及开槽钢筋制作了 21个不同参数的接头试件,并进行单向拉伸试验.结果表明:试验范围内接头试件钢筋临界锚固长度在5d和6d(d为钢筋直径)之间,锚固长度小于临界锚固长度时,钢筋发生刮犁式拔出破坏,大于临界锚固长度时,钢筋发生...     

混凝土单轴动态受拉损伤试验研究

混凝土结构在使用过程中,都要遭受地震、爆炸、冲击等动态荷载作用,在动态荷载作用下,混凝土的动态特性及损伤特性将发生很大改变.通过在MTS试验机上对普通混凝土受拉试件在应变率10-5%～10-1/s范围内进行动态单轴直接拉伸试验,以切线模量的退化来量度损伤,从损伤的角度把混凝土受拉应力一应变上升段曲线分为3个阶段,即初始损伤未发展阶段、损伤稳定发展阶段、损伤不稳定阶段.研究表明,随着应变率的变化,损伤未发展阶段的最大应力水平也随之增加.同时分析了动态荷载下混凝土的抗拉强度、弹性模量、临界应变及泊松比的变化,结果表明混凝土的弹性模量和泊松比随着应变率的增加变化不大;混凝土的抗拉强度、临界应变与应变率之间呈线性关系,并给出了抗拉强度、临界应变受应变率影响的经验公式.     

Dynamic failure analysis on granite under uniaxial impact compressive load

High strain-rate uniaxial compressive loading tests were produced in the modified split Hopkinson pressure bar (SHPB) with pulse shaper on granite samples. It was shown that the failure of the granite cylinder was typical tensile splitting failure mode by sudden splitting parallel to the direction of uniaxial compressive loading at different strain rates. Besides, it was concluded that not only the strength of granite increased, but also the fragment size decreased and the fragment numbers increased with the increasing strain rate. To quantitatively analyze the failure phenomena, the numerical calculation based on a dynamic interacting sliding microcrack model was adopted to investigate the influence of microcrack with the different initial crack length, crack angle, crack space and friction coefficient on the macro-mechanical properties of granite under different strain rates. Accordingly, the strain-dependency of the compression strength and the fragmentation degree of granite was explained reasonably.     

Strength degradation of sandstone and granodiorite under uniaxial cyclic loading

Change in mechanical properties of rocks under static loading has been widely studied and documented. However, the response of rocks to cyclic loads is still a much-debated topic. Fatigue is the phenomenon when rocks under cyclic loading fail at much lower strength as compared to those subjected to the monotonic loading conditions. A few selected cored granodiorite and sandstone specimens have been subjected to uniaxial cyclic compression tests to obtain the unconfined fatigue strength and life. This study seeks to examine the effects of cyclic loading conditions, loading amplitude and applied stress level on the fatigue life of sandstone, as a soft rock, and granodiorite, as a hard rock, under uniaxial compression test. One aim of this study is to determine which of the loading conditions has a stronger effect on rock fatigue response. The fatigue response of hard rocks and soft rocks is also compared. It is shown that the loading amplitude is the most important factor affecting the cyclic response of the tested rocks. The more the loading amplitude, the shorter the fatigue life, and the greater the strength degradation. The granodiorite specimens showed more strength degradation compared to the sandstone specimens when subjected to cyclic loading. It is shown that failure modes of specimens under cyclic loadings are different from those under static loadings. More local cracks were observed under cyclic loadings especially for granodiorite rock specimens.     

Dynamic failure analysis on granite under uniaxial impact compressive load

High strain-rate uniaxial compressive loading tests were produced in the modified split Hopkinson pressure bar (SHPB) with pulse shaper on granite samples. It was shown that the failure of the granite cylinder was typical tensile splitting failuremode by sudden splitting parallel to the direction of uniaxial compressive loading at different strain rates. Besides, it was concluded that not only the strength of granite increased, but also the fragment size decreased and the fragment numbers increased with the increasing strain rate. To quantitatively analyze the failure phenomena, the numerical calculation based on a dynamic interacting sliding microcrack model was adopted to investigate the influence of microcrack with the different initial crack length, crack angle, crack space and friction coefficient on the macro-mechanical properties of granite under different strain rates. Accordingly, the strain-dependency of the compression strength and the fragmentation degree of granite was explained reasonably. __________ Translated from Chinese Journal of Geotechnical Engineering, 2007, 29(3): 385–390 [译自: 岩土工程学报]     

花岗岩在单轴冲击压缩荷载下的动态断裂分析

利用脉冲整形器改进后的分离式Hopkinson压杆(SHPB)系统,对新加坡Bukit Timah地区的花岗岩圆柱形试样进行了高应变率下的单轴压缩实验。实验结果发现:随着应变率的增加,不仅花岗岩材料的抗压强度增大,而且以轴向拉伸劈裂为主要破坏形式的破碎程度也有所提高,表现为碎块的尺寸减小和数量增加。针对上述花岗岩的动态特性,采用多裂纹相互作用的动态滑移型裂纹模型定量的分析了不同应变率下,材料的微裂纹的初始长度、角度、初始裂纹间距以及裂纹面的摩擦系数等微裂纹特征对材料动态强度及破碎的影响,将岩石类材料的宏观动力学特性与其细观微结构联系起来,合理地解释了花岗岩的动态强度及破碎程度的应变率相关性。     

Inconsistency of changes in uniaxial compressive strength and P-wave velocity of sandstone after temperature treatments

It is generally accepted that the uniaxial compressive strength(UCS)and P-wave velocity of rocks tend to decrease simultaneously with increasing temperature.However,based on a great number of statistical data and systematic analysis of the microstructure variation of rocks with temperature rising and corresponding propagation mechanism of elastic wave,the results show that(1)There are three different trends for the changes of UCS and P-wave velocity of sandstone when heated from room temperature(20
C or 25
C)to 800
C:(i)Both the UCS and P-wave velocity decrease simultaneously;(ii)The UCS increases initially and then decreases,while the P-wave velocity decreases continuously;and(iii)The UCS increases initially and then fluctuates,while the P-wave velocity continuously decreases.(2)The UCS changes at room temperaturee400
C,400
Ce600
C,and 600
Ce800
C are mainly attributed to the discrepancy of microstructure characteristics and quartz content,the transformation plasticity of clay minerals,and the balance between the thermal cementation and thermal damage,respectively.(3)The inconsistency in the trends of UCS and P-wave velocity changes is caused by the change of quartz content,phase transition of water and certain minerals.     

砂岩直接拉伸蠕变特性及 Burgers 模型的改进与应用

应用自行研制的岩石直接拉伸装置对红砂岩进行了单轴直接拉伸蠕变试验,试验结果表明,在低应力状态下砂岩的直接拉伸蠕变由衰减蠕变和稳态蠕变组成,高应力状态下砂岩直接拉伸出现历时较短的加速蠕变阶段。在对蠕变特性分析的基础上对 Burgers 蠕变模型进行了改进,引入了一个非线性黏塑性体,并基于 BFGS 算法对拉伸作用下蠕变试验结果进行直接拟合。结果表明,基于 BFGS 算法的改进 Burgers 蠕变模型理论曲线与试验曲线吻合效果较好,引入模型的非线性黏塑性体其黏性系数 η _N 的初始值较大（ 10¹⁹ 以上）,该非线性黏塑性体在砂岩的加速蠕变阶段起到主导作用;改进 Burgers 模型不仅可以描述砂岩直接拉伸状态下的衰减蠕变和稳态蠕变阶段,而且可很好地描述砂岩加速蠕变过程。