Tensile Strength of Geological Discontinuities Including Incipient Bedding, Rock Joints and Mineral Veins
Tensile Strength of Geological Discontinuities Including Incipient Bedding, Rock Joints and Mineral Veins
复制标题
DOI：
10.1007/s00603-016-1041-x
复制
发表时间：
2016-07
影响因子：
6.2
通讯作者：
J. Shang;S. Hencher;L. J. West
中科院分区：
文献类型：
--
作者：
J. Shang;S. Hencher;L. J. West
地质不连续面在强度、变形性和渗透性方面对许多岩石工程项目具有控制性影响，但它们的表征往往非常困难。虽然不连续性通常被模拟为缺乏任何强度，但在许多岩体中，可见的岩石不连续性只是初始的，其拉伸强度可能接近甚至超过母岩的拉伸强度。这一事实对于真实的岩体表征非常重要，但通常被忽视。有人认为，目前的ISRM和其他标准的岩体表征，以及岩体分类计划，如RMR和Q，不允许充分的初期性质的许多岩石断裂或其地质变异性，需要进行修订，至少在概念上。本文讨论了岩石中初期不连续面的抗拉强度问题，并提出了一个实验室试验方案，以量化这一参数的结果。含有可见的、自然的初始不连续面（包括节理、层理和矿脉）的岩石样本已在直接拉伸中进行了测试。已经证实，这种结构面可以具有高抗拉强度，接近母岩的抗拉强度。当然，其他人则弱得多。在轴向应变小于0.5%的直接拉伸条件下，测试的地质结构面都表现出脆性破坏。三个因素有助于早期岩石结构面的抗拉强度进行了研究和表征。区分仅部分发育的不连续部分、局部风化留下局部残留岩桥的不连续部分和通过次生胶结作用“愈合”的不连续部分。对砂岩中的层面进行的测试表明，相邻初始层面的抗拉强度可能会有很大差异。在这一特定系列的试验中，层面的抗拉强度值范围为母岩强度的32%至88%（完整，无可见的不连续性），这种变异性可归因于地质因素。对初期矿脉的测试也显示出相当大的分散性，其强度取决于矿脉发育的地质性质以及是否存在岩桥。正如所料，初期岩石节理的抗拉强度随着风化程度的降低而降低，如岩石桥附近的颜色变化所示。岩石桥（缺乏显着变色）的抗拉强度被认为是类似的母岩。结果表明，在岩体分类和工程设计过程中，需要区分岩体结构面的初始程度，最好参照相对于母岩的抗拉强度来区分。有人认为，科学的岩体表征可以通过更好地欣赏地质历史在一个网站，从而提高预测和外推性能的过程中。
Geological discontinuities have a controlling influence for many rock-engineering projects in terms of strength, deformability and permeability, but their characterisation is often very difficult. Whilst discontinuities are often modelled as lacking any strength, in many rock masses visible rock discontinuities are only incipient and have tensile strength that may approach and can even exceed that of the parent rock. This fact is of high importance for realistic rock mass characterisation but is generally ignored. It is argued that current ISRM and other standards for rock mass characterisation, as well as rock mass classification schemes such as RMR and Q, do not allow adequately for the incipient nature of many rock fractures or their geological variability and need to be revised, at least conceptually. This paper addresses the issue of the tensile strength of incipient discontinuities in rock and presents results from a laboratory test programme to quantify this parameter. Rock samples containing visible, natural incipient discontinuities including joints, bedding, and mineral veins have been tested in direct tension. It has been confirmed that such discontinuities can have high tensile strength, approaching that of the parent rock. Others are, of course, far weaker. The tested geological discontinuities all exhibited brittle failure at axial strain less than 0.5 % under direct tension conditions. Three factors contributing to the tensile strength of incipient rock discontinuities have been investigated and characterised. A distinction is made between sections of discontinuity that are only partially developed, sections of discontinuity that have been locally weathered leaving localised residual rock bridges and sections that have been ‘healed’ through secondary cementation. Tests on bedding surfaces within sandstone showed that tensile strength of adjacent incipient bedding can vary considerably. In this particular series of tests, values of tensile strength for bedding planes ranged from 32 to 88 % of the parent rock strength (intact without visible discontinuities), and this variability could be attributed to geological factors. Tests on incipient mineral veins also showed considerable scatter, the strength depending upon the geological nature of vein development as well as the presence of rock bridges. As might be anticipated, tensile strength of incipient rock joints decreases with degree of weathering as expressed in colour changes adjacent to rock bridges. Tensile strengths of rock bridges (lacking marked discolouration) were found to be similar to that of the parent rock. It is concluded that the degree of incipiency of rock discontinuities needs to be differentiated in the process of rock mass classification and engineering design and that this can best be done with reference to the tensile strength relative to that of the parent rock. It is argued that the science of rock mass characterisation may be advanced through better appreciation of geological history at a site thereby improving the process of prediction and extrapolating properties.