Strength, deformation modulus and failure modes of cubic analog specimens representing macroporous rock
Strength, deformation modulus and failure modes of cubic analog specimens representing macroporous rock
复制标题
DOI：
10.1016/j.ijrmms.2010.08.015
复制
发表时间：
2010-12-01
影响因子：
7.2
通讯作者：
Hudyma, Nick
中科院分区：
文献类型：
--
作者：
Jespersen, Colleen;MacLaughlin, Mary;Hudyma, Nick
众所周知，岩体和实验室样本中的不连续性（包括孔隙度）会影响岩石的工程特性。 Discontinuities are often assumed to be evenly distributed throughout a rock mass or laboratory specimen.许多研究人员研究了孔隙率对实验室样品中弹性性能和裂纹扩展的影响，并在各种出版物中发表了精彩的总结，最著名的是 [1, 2]。在处理微孔性时，通常采用基本的连续方法。假设微观孔隙度均匀分布在岩体或样本内，因此，数值模型中不考虑微孔隙的分布。均匀加载样本可产生平滑的应力-应变曲线。微孔率的增加表现为样品强度和刚度的降低。大孔隙度，即肉眼可见的孔隙，对岩石表征提出了特殊的挑战。由于在尤卡山拟建的高级核废料处置库中进行了大量的表征研究，岩石力学界对大孔隙度很熟悉。大孔隙度并不是岩浆凝灰岩所特有的；大孔隙也存在于多孔玄武岩 [3] 和风化（多孔）石灰岩 [4] 中。尽管上述三种情况下大孔隙的地质形成不同，但大孔岩石有一个重要特征是一致的：大孔隙在整个岩体或实验室标本中的分布并不均匀。据了解，强度和弹性模量与孔隙度成反比，但这种关系因分散性而变得模糊不清[5]，对于大孔岩石尤其如此。在处理大孔隙度时，可以使用连续介质和不连续介质方法，但必须使用任一方法将单个大孔隙纳入岩体或实验室样本中。大孔分布通常是不均匀的，因此，大孔岩石的破坏不太可预测。在大孔隙度的极端情况下，甚至可能难以获得具有代表性的实验室样本，因为大孔的尺寸可能接近甚至大于实验室样本的直径。在施加的载荷下，大孔周围的应力场相互作用可能会产生不均匀的变形。均匀压缩载荷下的大孔岩石经常在拉伸时失效，并且岩石的工程特性变得越来越难以评估。已经使用多种不同的方法研究了空隙尺寸和形状以及工程性能之间的关系。大孔岩石（例如 [3, 6–8]）和由低刚度夹杂物制备的合成材料制备的模拟样本 [9, 10] 都经过了测试。近似解析解（有效介质理论）已被用来估计实验和数值数据的上限和下限[11]，以及用于描述上限和下限的实验数据的统计分析[12]。压缩测试已使用线弹性有限元和线弹性有限差分计算机模型 [9,10,13] 以及块状（通用不同元素代码 (UDEC)[14] 和基于粒子（粒子流代码 (PFC)[15]）不同元素计算机模型进行模拟。
It is well established that discontinuities, including porosity, within rock masses and laboratory specimens influence the engineering properties of rock. Discontinuities are often assumed to be evenly distributed throughout a rock mass or laboratory specimen. Numerous researchers have investigated the effect of porosity on both elastic properties and crack growth within laboratory specimens and excellent summaries presented in various publications, most notably [1, 2]. When dealing with microporosity, a basic continuum approach is often incorporated. It is assumed that microscopic porosity is uniformly distributed within a rock mass or specimen and as such, the distribution of micropores is not accounted for in numerical models. Uniform loading of specimens produces smooth stress–strain curves. An increase in microporosity is manifested by a decrease in specimen strength and stiffness. Macroporosity, or pores that are visible to the unaided eye, presents a special challenge in rock characterization. Macroporosity is familiar to the rock mechanics community because of the numerous characterization studies conducted at the proposed high-level nuclear waste repository at Yucca Mountain. Macroporosity is not specific to lithophysal tuff; macroporosity is also present in vesicular basalts [3] and weathered (vuggy) limestone [4]. Although the geological formation of macroporosity in the aforementioned three cases is different, there is one important characteristic of macroporous rock that is consistent: macropores are not evenly distributed throughout a rock mass or laboratory specimen. Strength and elastic modulus are understood to be inversely related to porosity, but the relationship is clouded by scatter [5], and this is especially true for macroporous rock. When dealing with macroporosity, both continuum and discontinuum approaches can be used, but individual macropores must be incorporated into the rock mass or laboratory specimen using either approach. Macropore distribution is typically non-homogeneous and consequently, the failure of macroporous rock is less predictable. In extreme cases of macroporosity, it may even be difficult to obtain representative laboratory specimens because the size of the macropores may approach or even be greater than the diameter of the laboratory specimen. Under an applied load, stress field interactions around macropores may produce non-uniform deformations. Macroporous rock under uniform compressive load often fails in tension, and the engineering properties of the rock become increasingly difficult to assess. The relationship between void size and shape, and engineering properties has been investigated using a number of different approaches. Both macroporous rock (for example [3, 6–8]), and analog specimens prepared from synthetic material prepared with low stiffness inclusions [9, 10] have been tested. Approximate analytical solutions (effective medium theories) have been used to estimate both the upper and lower bounds of experimental and numerical data [11], and statistical analysis of experimental data for the description of upper and lower bounds [12]. Compression tests have been simulated with both linear elastic finite element and linear elastic finite difference computer models [9, 10, 13] as well as blocky (universal distinct element code (UDEC)[14] and particlebased (particle flow code (PFC)[15]) distinct element computer models.