石英颗粒团聚体中high pressure压实的微观力学
Micromechanics of high pressure compaction in granular quartz aggregates
摘要：
多孔砂岩的力学行为通常使用颗粒力学的概念来建模，通常忽略了胶结作用的影响。为了探讨砂和砂岩力学之间的关键差异，我们在$5-40$ MPa有效围压下对渥太华石英砂进行了三轴变形实验。在$5$ MPa下，样品能够膨胀。在较高的约束下，聚集体显示连续压实，显示应变硬化。应力-应变行为是非线性的，并且不能准确地确定非弹性压实的确切开始。实测P波速度显示各向异性的发展。随着轴向应变的增加，沿轴向的速度趋于增加，而垂直于压缩轴的速度趋于减小（在低压下）或保持恒定（在高压下）。在高压条件下变形的样品中，声发射事件的位置是扩散的。显微结构的调查表明，增加颗粒破碎和破碎的围压增加，但没有证据表明，可以观察到的局部压实。孔隙流体的性质，无论是癸烷还是水，在应变速率为$10^{-6}$至$10^{-4}$ $s^{-1}$时，不会显著影响力学行为。晶粒的棱角性和粒度分布也没有显着改变的机械行为。我们推断，我们的观察表明，缺乏胶结介绍了额外的自由度的晶粒滑动，旋转，并在样品尺度重组，排除了存在和可持续性的应力集中超出晶粒尺度。这导致渐进压实和硬化，以及缺乏压实局部化。
英文摘要：
The mechanical behaviour of porous sandstones is generally modelled using concepts from granular mechanics, often overlooking the effect of cementation. To probe the key differences between sand and sandstone mechanics, we performed triaxial deformation experiments on Ottawa quartz sand at $5-40$ MPa effective confining pressure. At $5$ MPa, the samples are able to dilate. At higher confinement, the aggregates show continuous compaction, displaying strain hardening. The stress-strain behaviour is non-linear and the exact onset of inelastic compaction could not be determined accurately. Measured P-wave velocities show the development of anisotropy. With increasing axial strain, the along-axis velocities tend to increase, while velocities perpendicular to the compression axis tend to decrease (at low pressure) or remain constant (at high pressure). In samples deformed under elevated pressure conditions, acoustic emission event locations are diffuse. Microstructural investigations show an increase in grain chipping and crushing with increasing confining pressure, but no evidence of localised compaction could be observed. The nature of the pore-fluid, either decane or water, does not significantly influence the mechanical behaviour at strain rates of $10^{-6}$ to $10^{-4}$ $s^{-1}$. Grain angularity and grain-size distribution also did not significantly change the mechanical behaviour. We infer that our observations indicate that the lack of cementation introduces additional degrees of freedom for grains to slide, rotate, and reorganise at the sample-scale, precluding the existence and sustainability of stress concentrations beyond the grain-scale. This results in progressive compaction and hardening, and lack of compaction localisation.
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