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1.
循环围压对饱和软黏土永久变形的影响 总被引：1，自引：0，他引：1
通过对温州典型饱和软黏土进行一系列不同应力路径下的部分排水循环动三轴试验,研究了部分排水条件下循环围压对饱和软黏土变形特性的影响。试验结果表明：部分排水条件下,与常规的围压保持恒定,偏应力单独循环作用下的三轴试验结果相比,循环围压的存在对饱和软黏土的永久体应变和永久轴向应变均产生了的显著的影响。在相同循环应力比和循环次数下,试样的永久体应变和永久轴向应变均随着循环围压幅值的增大而增大,说明常规的恒定围压循环三轴试验会低估高速交通荷载作用下路基土体的沉降。基于试样第10 000圈的永久体应变和永久轴向应变,分别建立了可以量化部分排水条件下循环围压对饱和软黏土永久体应变和永久轴向应变影响的经验公式,并用于预测饱和软黏土在交通荷载这种包含循环偏应力和循环围压耦合作用的复杂应力条件下产生的永久变形。 相似文献
2.
利用自主研发的含瓦斯煤岩热流固耦合三轴伺服渗流装置配合声发射监测系统对不同围压作用下含瓦斯煤岩进行了卸围压试验,试验结果表明:不同围压作用下含瓦斯煤岩声发射事件率、累积振铃计数与应力曲线具有较好的对应关系,振幅总体分布在[42,60]dB之间,随着振幅的增加,声发射事件率呈现出递减的趋势;含瓦斯煤岩失稳破坏时声发射事件率与围压呈线性关系,而声发射累积振铃计数与围压呈指数函数关系;不同围压下含瓦斯煤岩卸围压实验中轴向应力加载阶段和围压卸载阶段能量特征是不同的,随着围压的增大,煤岩加载阶段吸收的能量明显增大,卸载阶段释放的能量也相应的增大,加载阶段和卸载阶段能量变化与初始围压均呈对数关系。 相似文献
3.
对英安岩岩样开展单轴、常规三轴加荷和三轴卸荷试验,并对试验过程进行声发射监测,研究在3种应力路径下英安岩变形破坏过程的声发射b值特征差异,探索声发射b值在岩石破坏前兆方面的规律。研究结果表明:英安岩岩样的声发射b值特征与加载的应力路径关系密切,加荷路径即单轴路径和常规三轴路径下b值变化规律相似,加荷与卸荷路径下b值变化规律差异较大。单轴和常规三轴加荷试验中,围压对声发射b值特征有较大的影响。围压越大,岩样在破坏前,b值的整体水平越高。岩样在破坏时,声发射b值下降幅度越大、降低速率越快,且b值达到整个过程中的最小值。三轴卸荷试验中,围压对声发射b值特征影响不明显。与常规三轴试验相比,三轴卸荷试验在卸荷至一定水平后,其b值整体水平更低,最终破坏时b值的最小值更小。提出当岩样峰值强度后存在明显的应力跌落,此时声发射b值的快速下降可以作为破坏前兆。b值的临界值要通过大量室内岩石声发射试验的统计结果来确定。将声发射b值快速下降、临界值突破0.6作为试验英安岩岩样的破坏前兆。 相似文献
4.
A large triaxial investigation of the stress-path-dependent behavior of compacted rockfill 总被引：1，自引：1，他引：0
Realistic prediction of the deformation of rockfill structures becomes increasingly important, which requires improved knowledge about the mechanical properties of rockfill materials. However, previous large triaxial tests were usually carried out with a constant cell pressure, and there is uncertainty about the behavior of rockfill along other stress paths. This paper presents the results of a series of large triaxial tests conducted on limestone rockfill specimens along different loading paths. The effect of previous loading history and moisture content has also been investigated. The results show that the stress?Cstrain and volumetric behavior of rockfill are significantly influenced by the loading directions as well as the confining pressures. However, the stress path appears to have only minor influence on the shear strength of rockfill, while the strength envelope exhibits pronounced curvature at low confining pressures and the peak friction angle decreases approximately linearly with the logarithm of the corresponding confining pressure. The previous loading history is revealed to have considerable effect on the stress?Cstrain behavior but small influence on the peak strength of rockfill. In contrast, the moisture content of rockfill has marked influence on both the deformation and the strength characteristics. The implications of the test results are discussed. 相似文献
5.
Rock Mechanical Characterization of an Argillaceous Host Rock of a Potential Radioactive Waste Repository 总被引：2，自引：0，他引：2
Summary The physical properties of foliated marls and shales from the Swiss Central Alps were investigated in the laboratory as part
of the site characterization of a potential low and intermediate level radioactive waste repository. The rocks were first
characterized by density, porosity and water content, then P-wave velocity measurements and uniaxial compression tests were
conducted on samples oriented parallel, perpendicular and ∼45° inclined to the foliation. Correlations between P-wave velocities,
Young's moduli, and uniaxial strengths and directional dependence of compressibility and permeability (determined at elevated
hydrostatic pressures) revealed that two distinct families of microcracks cause the significant anisotropy. The pressure and
time dependence of strength was then measured in triaxial compression, creep, and relaxation tests. In triaxial compression
at room temperature, confining pressures up to 90 MPa and strain-rates as low as 10−8 s−1 failure occured after small inelastic strains. Failure strength exhibits a strong pressure and a weak strain-rate dependence.
The low friction coefficient of clay minerals appears to dominate the bulk frictional properties. Micromechanical modeling
of triaxial compression, creep, and relaxation tests suggests that inelastic deformation is accommodated by subcritical crack
growth. 相似文献
6.
分级循环荷载作用下冻土动应变幅值的试验研究 总被引：1，自引：0，他引：1
通过低温动三轴试验,采用分级加载方式逐级施加动荷载,对不同加载频率、围压和负温条件下青藏冻结黏土和兰州黄土的动应变幅值变化特征进行了试验研究。结果表明,同一级荷载作用下,动应变幅值随振次的增加基本不变,可以采用平均值来反映各级加载下的动应变幅值;不同加载频率、围压和温度条件下,动应变幅值随动应力幅值的变化规律相同,即随着动应力幅值的增加,动应变幅值逐渐增大;动应变幅值随加载频率的增加而减小,但减小的速率逐渐降低,动应变幅值最终趋于一稳定值,对于青藏黏土和兰州黄土,该稳定值均随加载级数的增加而增加;随着围压的增加,青藏黏土的动应变幅值变化不大,而兰州黄土的动应变幅值呈逐渐减小的趋势;动应变幅值随温度的降低而减小。动应力幅值对动应变幅值的影响最大,动荷载振动频率的影响次之,温度的影响第三,围压的影响最小。 相似文献
7.
8.
地下洞室开挖围岩经历典型径向卸载、环向加载应力路径,由此引起的岩体强度、变形特征和破坏机制也不尽相同。针对锦屏二级水电站高地应力赋存环境,对施工排水洞大理岩开展常规单轴全应变、三轴压缩、卸围压、卸围压-加载轴压等4种不同应力路径力学试验,得到应力-应变全过程曲线、变形破坏特征和极限储能变化规律。试验研究结果表明, （1）锦屏二级水电站大理岩破坏时轴向应变一般较小,为硬脆性材料,卸荷应力路径下该脆性特征更为明显;（2）卸围压同时加载轴压试验峰值强度对应轴向应变、环向应变及体积应变值一般高于单纯的卸围压值,而对应峰值强度则一般低于卸围压值;（3）卸荷速率较大时,变形模量越大,大理岩峰值强度越低。加载速率越大,变形模量越小,峰值强度越高。初始围压越高,变形模量值越低,峰值强度越高;（4）无侧限作用时试件主要为张拉破坏,低侧限作用时为剪切破坏为主,局部存在张拉破坏,较高侧限时,剪切面为典型X或Y型;（5）岩石试件具有极限储能值,该值受多种因素的影响。一般情况下试件破坏对应围压越高,极限储能值越高,卸载速率越大,极限储能值越小。研究结果对于岩爆孕育发生机制解释以及工程实际问题的解决均有参考价值。 相似文献
9.
三轴应力状态下盐岩强度分析探讨 总被引：1，自引：0，他引：1
通过分析盐岩在三轴应力状态下的变形,说明了较高围压下盐岩的大变形特性,提出了三轴应力状态下,利用轴向荷载除以试件初始横截面面积得到应力-应变关系存在的问题,据此对工程应变和对数应变进行了分析和对比,阐明了这两种应变的适用条件,并开展了不同围压下的试验测试和对试验结果对比分析。研究揭示了应利用对数应变分析盐岩的大变形特性和对变形后的应力进行修正,得到了盐岩的工程应变和对数应变均可表示为围压的线性函数,围压为20 MPa时的轴向压缩变形量是5 MPa时的3.09倍。围压越高,对数应变修正得到的最大轴向应力与不修正的差值越大,用对数应变修正后的轴向应力低于不修正的结果,围压达到20 MPa时,前者仅为后者的63.85%。 相似文献
10.
不同应力路径下绢云母片岩粗粒料声发射特征 总被引：1，自引：0，他引：1
粗粒料在变形和颗粒破碎过程中伴随着明显的声发射（AE）,通过监测粗粒料在外力作用下的声发射信号特征可用来研究其力学机制。为探讨不同应力路径下绢云母片岩粗粒料声发射规律,采用改装设计的大型三轴试验机,对绢云母片岩粗粒料分别开展了常规三轴固结排水、等p（体应力）和等q（偏应力）应力路径试验,同时监测其声发射信号。研究表明,对于粗粒料的声发射必须考虑颗粒间的滑动摩擦、翻滚摩擦、颗粒破碎这3种细观机制。不同围压、不同应力水平对颗粒间的滑移、翻滚以及颗粒破碎活动影响较大,因此,在不同阶段,摩擦型AE与破碎型AE所占比例各不相同。在等p路径下,当累计声发射信号出现拐点时,可判断其为应变软化点。等q试验产生的累计AE计数与累计AE能量计数要比等p试验的累计AE计数和累计AE能量计数少一个量级,说明等p试验状态下的声发射要比等q试验活跃。等p试验中,随着体应力逐渐增大,累计AE参量增长率逐渐增大,而等q试验中,随着偏应力逐渐增大,累计AE参量增长率逐渐降低。 相似文献
11.
重塑超固结上海软土力学特性及弹塑性模拟 总被引：1，自引：0，他引：1
对典型上海软土重塑样进行了围压不变和平均主应力不变的三轴排水剪切试验,得到重塑上海软土在不同初始超固结比和围压条件下的应力-应变关系,弄清了超固结比、围压以及应力路径对重塑上海软土的变形和强度特性的影响;根据土体的应力-应变曲线得到重塑上海软土的临界状态应力比及内摩擦角。采用姚仰平等建议的基于伏斯列夫面的超固结土本构模型,并根据等向压缩及三轴排水剪切试验确定其模型参数,对保持围压和平均主应力不变的三轴压缩试验进行了模型预测。预测结果表明,此超固结土本构模型能较好地反映重塑超固结上海软土的变形和强度特性。 相似文献
12.
Influence of Loading Rate on Deformability and Compressive Strength of Three Thai Sandstones 总被引：1，自引：0，他引：1
Uniaxial and triaxial compressive strength tests have been performed using a polyaxial load frame to assess the influence
of loading rate on the strength and deformability of three Thai sandstones. The applied axial stresses are controlled at constant
rates of 0.001, 0.01, 0.1, 1.0 and 10 MPa/s. The confining pressures are maintained constant at 0, 3, 7 and 12 MPa. The sandstone
strengths and elastic moduli tend to increase exponentially with the loading rates. The effects seem to be independent of
the confining pressures. An empirical loading rate dependent formulation of both deformability and shear strength is developed
for the elastic and isotropic rocks. It is based on the assumption of constant distortional strain energy of the rock at failure
under a given mean normal stress. The proposed multiaxial criterion well describes the sandstone strengths within the range
of the loading rates used here. It seems reasonable that the derived loading rate dependent equations for deformability and
shear strength are transferable to similar brittle isotropic intact rocks. 相似文献
13.
Rock mechanical behaviors and deformation characteristics are associated with stress history and loading path. Unloading conditions occur during the formation of a salt cavity as a result of washing techniques. Such conditions require an improved understanding of the mechanical and deformation behaviors of rock salt. In our study, rock salt dilatancy behaviors under triaxial unloading confining pressure tests were analyzed and compared with those from conventional uniaxial and triaxial compression tests. The volume deformation of rock salt under unloading was more than under triaxial loading, but less than under uniaxial loading (with the same deviatoric stress). Generally, under the same axial compression, the corresponding dilatancy rate decreased as the confining compression increased, and under the same confining compression, the corresponding dilatancy rate increased as the axial compression increased. The dilatancy boundary of the unloading confining pressure test began with unloading. This is different from the dilatancy of the uniaxial and triaxial compression tests. The accelerated dilatancy point boundary stress value was affected by confining and axial compressions. The specimens entered into a creep state after unloading. The associated creep rate depends on the deviatoric stress and confining compression values at the end of the unloading process. Based on unloading theory and the experimental data, we propose a constitutive model of rock salt damage. Our model reflects the dilatancy progression at constant axial stress and reduced lateral confinement. 相似文献
14.
Conventional triaxial compression and “reducing confining pressure” experiments were carried out for red sandstone by an MTS815 Flex Test GT rock mechanics experimental system. Our results show that the post-peak axial deformation characteristics of red sandstone changed as the confining pressure was increased from 5 to 65?MPa. Young’s modulus of red sandstone increased nonlinearly with increasing confining pressure, but Poisson’s ratio remained unaffected. Using our new data, the compactive and dilatant behavior, strength and failure characteristics of sandstone under triaxial compression are further discussed. For our data, the nonlinear Hoek-Brown criterion better reflects the peak strength properties than the linear Mohr-Coulomb criterion. However, the residual strength shows a clear linear relationship with confining pressure, which can be best described using the linear Mohr-Coulomb criterion. The peak and residual strengths were not directly related to the two different loading paths. The onset of dilatancy (C′), the switch from compaction-dominated to dilatant-dominated behavior (D′) and the stress at zero volumetric strain all increased linearly with the confining pressure. In our conventional triaxial compression experiments, the failure mode changed from mixed tension and shear fracture (single shear fracture) to shear fracture with double slippage planes with increasing confining pressure. However, the failure mode in our “reducing confining pressure” experiments was more complicated and results mainly from the unstable failure characteristics of the rock during the reduction in confining pressure. Finally, based on our acoustic emission (AE) locations, at a confining pressure of 35?MPa, a detailed analysis of the evolutionary process of internal cracks is presented for the entire loading process. 相似文献
15.
为了揭示应力扰动和卸载围压作用下大理岩损伤破裂的物理过程和非线性力学行为,采用GCTS RTR-2000伺服加载岩石力学试验机进行了岩石疲劳卸围压试验,同时对破坏试样进行了压后裂纹形态CT扫描可视化分析。结果表明：周期性的加卸载作用对大理岩起到了主因损伤作用,卸围压的作用对大理岩起到了根本性的破坏作用。岩石疲劳循环形成滞回环,滞回环面积由疏变密,滞回环加载和卸载曲线接近重合,加卸载模量近似相等;岩石经过卸围压作用,岩石的轴向、径向和体积应变表现为不同程度增大,表明应变对围压降低具有强敏感性,敏感程度由高到低依次为体积应变、径向应变和轴向应变;由于疲劳循环的影响,卸围压作用产生的围压降幅随循环次数增多而降低,卸围压时长随循环次数增多而减少;量化宏观应变变形,求得应变损伤指数 、 、 ,疲劳循环次数越多,应变损伤指数越大;岩石破坏后细观CT扫描揭示了疲劳循环损伤对岩石破裂形态影响的内在机制。随疲劳循环次数的增加,裂纹密度和规模显著增加。研究成果可为地下工程疲劳活动规律和开挖卸荷问题提供理论和模型支撑。 相似文献
16.
循环加载时围压对岩石动力特性的影响 总被引：1，自引：0，他引：1
针对砂岩岩样,探讨了在不同围压作用下和轴向循环加载时岩样的动力力学性质,研究围压对砂岩岩样的动力力学性质的影响。采用的试验设备是MTS－815岩石和混凝土试验系统,5组围压分别为10、20、30、40、50 MPa。岩样为汶川地区的干砂岩,轴向荷载施加的频率为1 Hz。结果表明,（1）随着围压的逐渐增加,试样的残余轴向应变和体变逐渐增加,且剪胀发生时的残余体变也逐渐增加;（2）动力荷载作用时岩样在高围压比低围压下的初始刚度和强度高;（3）不同围压作用下,当应力比Rs较大时,岩样在较小的循环次数下发生破坏;（4）试样的破坏模式为剪切破坏,动力荷载作用下试样形成的局部化破坏带更宽。 相似文献
17.
为研究地下盐穴储气库受间歇性周期注、采循环载荷作用下围岩的非连续疲劳破坏演化过程,对取自巴基斯坦的深层盐岩进行了室内三轴间隔疲劳试验研究,并分析了三轴状态下不同围压、不同应力等级对盐岩间隔疲劳的影响。试验结果表明：（1）与单轴间隔疲劳相比,围压的存在不仅提高了盐岩的抗压强度,而且增加了盐岩的疲劳寿命,围压越高增加的幅度越明显。（2）三轴间隔疲劳试验中,盐岩间隔后循环中的残余应变大于间隔前的残余应变。这与单轴间隔疲劳得到的结果一致,但围压的上升会导致盐岩的残余变形积累速度以及间隔前后循环残余的变形差值都减小。（3）随着应力等级的升高,残余应变以及时间间隔前后的残余应变差值都呈现增大的趋势。 相似文献
18.
变质软岩路堤填料湿化变形规律研究 总被引：2，自引：0，他引：2
采用双线法,对十堰-天水高速公路安康西段的变质软岩路堤填料,在两种密度条件下进行了大型三轴试验,同一竖向偏应力下饱和与风干状态填料应变的差值即为湿化引起的应变,对其变化规律进行分析,结果表明：填料的湿化变形发展呈两个阶段,临界湿化应变的大小与竖向偏应力和围压的比值密切相关,同一密度、不同围压条件下的各曲线变化点的湿化应变值较为一致;填料密度增大,则变化点的湿化应变值增加,说明密度和围压不仅影响湿化变形的大小,还影响其发展规律。根据3种围压条件下的试验结果,对两种密度的填料,分别建立了填料湿化变形发展规律的公式,并用新的第4种围压条件下的试验结果进行校核,吻合程度较好。该公式可用于分析高速公路施工中路堤湿化变形的大小及发展规律。 相似文献
19.
围压循环变化将引起土体孔压累积,加剧土体累积塑性应变,导致地基灾变事故。为研究围压循环变化对饱和粉质黏土变形特性的影响,利用GDS双向振动三轴仪,进行部分排水时饱和粉质黏土的变围压循环三轴试验,研究不同应力路径斜率和循环动应力比时饱和粉质黏土的孔压、轴向累积塑性应变和体应变发展规律,建立部分排水条件时考虑循环围压和循环动应力耦合作用的地基粉质黏土累积应变数学模型。试验结果表明：部分排水时饱和粉质黏土孔压、轴向累积塑性应变和体应变均随循环动应力比和应力路径斜率的增大而增大;动孔压比随着振动次数的增加明显分为急剧增加、快速下降和持续平稳3个阶段;轴向累积塑性应变和体应变均随振动次数的增加而增大。当加载次数超过2 500次时,粉质黏土孔压趋于平稳,变形速率略有降低,但变形持续增加。补充试验结果表明,所建立模型与试验结果具有较高的一致性。研究结果将为交通循环荷载导致的地基灾变控制技术提供理论依据。 相似文献
20.
黄土地基动力沉降特性试验研究 总被引：2，自引：1，他引：1
路基工后沉降控制是客运专线路基工程研究的重点内容,其中地基在列车荷载长期重复作用下的累积沉降不可忽视。为揭示黄土地基在列车振动荷载长期作用下的沉降变形,通过对原状黄土试样的循环三轴试验,模拟实际列车荷载瞬时加载状态,采用不等向长持时加载,得出了在不同围压条件下黄土的动强度特性和循环应力-累积应变关系,并对较小循环应力下的循环应力-累积应变关系进行了归一化处理,得到了以下结论：①黄土的累积应变随时间的增加而增大,当循环应力不超过临界应力时,应变会最终达到稳定;反之,黄土结构遭到破坏,应变不能达到稳定;②不同围压下的黄土累积应变均随循环应力的增大而增大,且临界循环应力随围压的增大而增大。③在同一围压状态和同一应变破坏标准下,动强度随振次的增加而减小;④在不同围压、相同振次条件下达到相同的应变所需要的循环应力随围压的增大而增大;⑤在较小循环应力作用下,不同围压下黄土的累积应变随循环应力增加呈线性增长。 相似文献