三轴压缩条件下黏性土微细结构随荷载变化动态 调整的定量研究

土体在三轴压缩条件下的力学特性是研究土体在其他受荷条件下力学特性的基础,而土体在不同受荷条件下力学特性的差异,主要是由土体内部结构的差异性决定的。为研究黏性土在三轴压缩条件下内部结构的动态调整,利用自行研制的微细结构光学测试系统,对荷载作用下黏性土微细结构调整信息进行了连续采集,并做了定量分析。研究结果表明：孔隙和颗粒集聚体的变化存在一定的关联性;随着荷载的增加,颗粒集聚体排列向着杂乱无序的方向发展,孔隙定向性优于颗粒排列;在荷载作用下,土体通过自身形态的变化,排列形式的调整,逐步向稳定的承载形式过渡,使变形向逐渐减小的趋势发展。     

饱水红砂岩冻融特性试验研究

以西北地区多孔隙、易风化典型红砂岩为研究对象,研究冻融作用对红砂岩力学特性影响,分别测定1,2,3次冻融后不同围压条件下,常温/负温红砂岩物理力学参数.试验结果表明:1)3次冻融后,红砂岩表面未产生剥落或开裂现象,但孔隙率和损伤变量增大;2)随冻融次数增加,红砂岩强度和黏聚力逐渐减小,摩擦角增大,负温条件下红砂岩强度和黏聚力始终大于常温条件;3)强度影响系数随冻融次数增加而减小,随围压增加而增大,影响系数大于1时,围压对红砂岩强度的增强作用大于冻融对岩石强度的损伤作用;4)冻融后常温红砂岩压缩破坏主破裂面断面粗糙,有颗粒剥落,产生多条裂纹,破碎严重;负温红砂岩压缩破坏主要为单破裂面剪切破坏,无次裂纹产生.依据以上研究成果,建议冻结工程选用低发热的水泥和炸药,减少冻结壁暴露时间.     

考虑含水率影响的红砂岩损伤统计模型

为了描述红砂岩在不同含水率条件下的力学特性,通过对不同含水率的红砂岩进行单轴压缩试验,分析了含水率变化对其强度和变形特性的影响.结果表明：含水率小于3%时,红砂岩有较高的强度;含水率大于3%时,红砂岩的强度明显降低;但含水率超过6%后,强度衰减趋势显著变缓.含水率与弹性模量及峰值强度之间呈指数函数变化,而峰值强度对应的应变随含水率变化呈线性函数变化.将试验确定的关系式作为边界条件,运用损伤统计理论和Lemaitre应变等价性假说,推导出了能反映含水率影响的红砂岩损伤统计模型.     

吸附气体量对煤岩力学特性损伤劣化的试验研究

煤岩吸附气体后会导致强度降低等力学损伤,为定量研究吸附气体量对煤岩体力学特性损伤劣化规律,利用可视化恒容固气耦合试验系统开展了型煤吸附He,N_2,CH_4和CO_2后的单轴压缩试验,基于分形理论与MATLAB软件编程提取试验过程加载图像,得到了气-固耦合加载过程中煤体损伤劣化规律与裂隙发育分形演化特征.试验结果表明:不吸附的He对型煤力学特性没影响,随着型煤对于不同气体吸附量(N_2CH_4CO_2)的增加,煤体损伤劣化程度加剧:1)煤体强度分别降低了9.80%,27.11%和32.05%;2)全应力-应变曲线表明扩容点提前,损伤因子分别为0.053,0.237和0.323;3)型煤表面裂纹发育越来越丰富,密度增加并呈现"鱼鳞片"状膨胀脱落,具有明显的分形特征,经计算裂隙分形维数分别为1.41,1.43,1.46.     

冻结层状红砂岩三轴蠕变特性及本构模型研究

为探讨冻结、三轴应力条件下层状红砂岩蠕变失稳规律,采用自主研发的DRTS-500型动力扰动低温岩石三轴试验系统对-10℃,围压为8MPa下不同节理面倾角的层状红砂岩进行三轴压缩试验和三轴蠕变试验,建立了冻结层状红砂岩三维蠕变模型.结果表明:冻结层状红砂岩轴向初始蠕变特性、非线性蠕变特性以及蠕变破坏形式受层理方向影响显著;所提出的新模型可以精确描述冻结层状红砂岩在三轴压缩条件下的轴向、径向蠕变全过程曲线,且该模型在描述初始蠕变阶段和非线性蠕变阶段时优于经典西原模型和改进西原模型.研究成果对西北地区层状岩层中立井冻结法施工时冻结岩壁支护时间、非线性变形预测以及井筒安全性评价具有一定的参考价值.     

单轴压缩下不同含水率红砂岩声发射特性试验研究

采用高低两种不同频率的声发射通道,对3种不同含水率的红砂岩进行单轴压缩声发射试验,分析了不同含水率下的红砂岩力学特性与声发射特性.试验结果分析表明:随含水率增加,红砂岩峰值应变量呈下降趋势;两种不同的声发射通道中,随着含水率的增加,声发射振铃计数均减少,主要区别在于数量明显不同;同一种声发射通道中,含水率对高频通道中振铃计数率变化规律无明显影响.低频通道中,随着含水率的增加声发射振铃计数出现明显的"滞后"现象.     

基于声发射和能量演化规律评价岩石脆性的方法

基于声发射记录的能量和能量演化规律提出了一种新的评价岩石脆性的方法.通过不同加载速率下红砂岩的单轴压缩试验和不同温度下花岗岩的单轴压缩试验对新方法进行了检验,结果表明:红砂岩脆性随着加载速率增加而增大;花岗岩脆性随温度的升高存在2个阈值温度,第一阈值温度为200℃,第二阈值温度为800℃,与实际脆性程度相符.随后利用新的脆性评价方法分析了岩性、围压、层状岩石层理倾向及饱水对脆性的影响,数值显示:高水填充石、原煤、泥岩、砂岩、页岩、花岗岩的脆性依次增大,其中花岗岩的脆性指数是高水填充石的3.15倍;红岩石脆性随围压增大而减小,围压30MPa时其脆性指数相比单轴压缩时的脆性指数降低了21.5%;无论干燥还是饱水,层状砂岩随着层理倾角的增加,脆性先是快速增大后缓慢增大,90°砂岩的脆性指数在干燥和饱水下分别是0°时的1.80和1.34倍,饱水降低了层状砂岩的脆性.     

引江济淮试验工程软岩崩解特性及其影响因素试验研究

以引江济淮试验工程为依托,开展砂岩与泥岩的崩解特性试验研究。通过静态烘干-浸水崩解试验,研究不同风化程度的软岩在干湿循环作用下的崩解性状,同时进行耐崩解试验以及点荷载强度试验,揭示崩解性与强度、失水率的相关变化规律。试验表明:干湿循环作用和风化作用均会减弱岩石耐崩解能力;风化岩石的耐崩解指数与干燥岩石点荷载强度成正相关,与岩石的失水率成线性负相关;岩石的耐崩解性与岩石结构类型关系密切。     

硅粉高强混凝土单轴抗压强度的试验研究

混凝土是一种存在初始损伤的工程材料,其破坏过程是在外载荷作用下微细观尺度的损伤萌生、扩展、贯通,直到最后宏观裂纹产生导致混凝土失稳破裂的过程.通过对硅粉混凝土进行单轴压缩试验,分析了不同水灰比和28 d碳化龄期混凝土在单轴压缩条件下的破坏形态.     

摩擦型桩表面劣化时的沉降特性室内模拟试验

为研究工作荷载作用下,摩擦型桩(端承摩擦桩和摩擦桩)在腐蚀地基中发生表面劣化时的沉降特性,通过制作以硫酸铜溶液为腐蚀性介质的饱和砂土地基模型,开展了加速劣化试验,得到工作荷载作用下摩擦型桩表面发生劣化时的沉降规律.结果表明:腐蚀地基中,桩表面劣化程度随时间不断增大,沉降量随劣化程度的增大而增大;端承摩擦桩和摩擦桩的荷载-沉降曲线发展规律不同;在工作荷载作用下,经过17 360 min,端承摩擦桩的沉降量达到桩径的28.5%,其中表面劣化引起的沉降量为10.6%,大于摩擦桩的7%;试验结束时,端承摩擦桩和摩擦桩的沉降量均达到了各自极限承载力对应的沉降量.表面劣化导致摩擦型桩的沉降量显著增加,表面劣化引起的附加沉降可能影响桩的正常使用.     

压力水-岩耦合作用下砂岩断口微观破坏机理

为了研究流固耦合作用下岩石的损伤劣化机理,以砂岩岩样为研究对象,采用流固耦合力学实验系统开展轴压水压耦合作用下单轴压缩、三轴压缩及三轴蠕变实验,借助扫描电子显微镜对岩样破裂断口的微观结构特征进行分析。结果表明:单轴饱水岩样破裂断口表面比干燥岩样出现更多的裂纹核,且断口形貌以沿晶断裂为主,穿晶断裂为辅;随着水压增大,三轴压缩岩样破裂断口表面裂纹核逐渐变少,剪切平行裂纹逐渐增多,岩样的宏观破坏形式从以张拉破坏为主逐渐向以剪切破坏为主转变;与三轴压缩岩样断口相比,三轴蠕变岩样破裂断口表面平整度和光滑度较差,晶体间联结更加紧密,剪切裂纹密度和深度增加。     

A composite material model for investigation of micro-fracture mechanism of brittle rock subjected to uniaxial compression

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Effect of rock composition microstructure and pore characteristics on its rock mechanics properties

This paper is to study the influence of composition, microstructure and pore characteristics on the rock mechanical properties. Five kinds of sandstone compositions were analyzed by using X-ray diffraction instrument. And the microstructure was observed by using scanning electron microscope. Then the pore distribution characteristic was investigated by using the low field nuclear magnetic resonance equipment. Finally, the uniaxial compression test was carried out to investigate the mechanical characteristics by using RMT150C mechanics experimental system and the uniaxial compressive strength, Poisson's ratio and elastic modulus were obtained. Compared to the analysis of the composition, structure and pore distribution and mechanical properties of the five kinds of sandstones, the relationship among composition,structure, pore distribution and mechanical properties was obtained. The results show that the composition, microstructure, pore distribution and mechanical properties of sandstone are closely related.With the decrease of feldspar and quartz particles, the compressive strength and elastic modulus increase, while the porosity decreases.     

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.     

Consolidation and microstructures of microwave sintered W-25Cu alloys with Fe addition

W-25Cu alloys were microwave sintered in a 2.45 GHz multimode applicator. The densification, microstructure and their dependence on sintering mode and Fe addition were investigated in detail. Owing to the volumetric heating intrinsic in microwave processing, a microstructure with larger W grain size in center regions was observed as against larger grain size in edge regions for conventional sintering. Microwave sintering demonstrates its intrinsic advantages such as rapid heating rate, densification enhancement and microstructural homogeneity; but it undesirably promotes W grain growth. Under microwave sintering, the role of Fe addition on compact consolidation is not so substantial as under conventional sintering. Moreover Fe degrades the microstructural quality, generating worse uniformity and coarser W grains.     

Failure mechanism of full-size concrete filled steel circle and square tubes under uniaxial compression

In this paper, the failure mechanisms of full-size concrete filled steel tubes(CFST) under uniaxial compression were investigated with nonlinear finite element method. Existing experimental results were employed to verify the validity of the finite element models of CFST specimens. Then, the numerical analysis was further conducted to study the mechanical behaviors of full-size CFST columns with circular and square cross sections under uniaxial compression. The simulation results indicate that the distribution of the contact pressure between circular steel tube and core concrete is much more uniform than that between square steel tube and concrete, resulting in much higher confinement and more efficient interaction between steel tube and core concrete in circular CFST columns, as well as ultimate load capacity and ultimate displacement. Extensive parametric analysis was also conducted to examine the effect of various parameters on the uniaxial compression behaviors of circular and square CFST columns.     

岩石单轴压缩端部效应的数值实验研究

通过应用岩石破裂过程分析系统RFPA2D,模拟了不同刚度垫板下的岩石单轴压缩实验,对比刚性与柔性垫板,确认了端部效应的存在,通过不同刚度垫板下的岩石单轴压缩实验,分析了端部效应对试件的测试强度和破坏模式的影响。     

无粘性土中管涌的临界水头梯度研究

将管涌型无粘性土中的颗粒分为骨架颗粒、阻塞颗粒和可动颗粒三组，在分析骨架孔隙中可动颗粒受力的基础上，将总压力降分为骨架孔隙壁引起的压力降、骨架孔隙中静止颗粒引起的压力降及正在运动的颗粒引起的压力降三部分，从而得到了可动颗粒起动的临界水头梯度公式，对管涌试验的校验证实了该公式的有效性，计算结果表明：当有细颗粒流失后，级配不连续的管涌型土比级配连续的管涌型土更易发展成管涌破坏，同时还证实：随着可动颗粒的流失，管涌破坏可以转化为流土破坏。     

Microstructural morphology of the semi-solid high carbon steel T12 before and after rheo-rolling

The semi-solid high carbon steel T12 was rolled in a closed box groove under a certain condition by the rheo-rolling equipment, and the microstructural morphology of the semi-solid T12 before and after deformation was investigated by optical microscope to analyze and summarize the microstructure evolution law of T12 deformed in semi-solid state. The experiment results show that the grain shape before deformation of the semi-solid T12 steel displays globule or ellipse by the electromagnetic stirring,the distribution of solid and liquid phases is homogeneous. But the microstructure of semi-solid product after rheo-rolling exhibits macrosegregation that the distribution of liquid and solid phases changes, the liquid phases divorce from the solid phases. In the transverse section, most of the solid phases get together in the center of the specimen, the liquid phases flow to the surface or the edge of the specimen, and the grains occur plastic deformation while reduction increased. In longitudinal section, the middle microstructure of the specimen is more homogeneous than that at the head or tail, the head microstructure is similar to the tail and the size of the grains is not homogeneous.