Behaviour of sparsely fractured rock in low confining stresses

岩石破坏的萌生和扩展是岩石工程中的一个重要问题。为了了解作为工程材料的岩石和岩体的特性，有必要从完整岩石的特性入手。从工程角度来看，这涉及到研究实验室规模的样品，如直径在50毫米范围内的钻石钻芯。对于许多岩石类型，颗粒大小足够小，因此这种规模的样本可以被认为代表了更大的完整岩石体积。 在确定岩石的完整强度时，需要进行几项实验室测试。更常见的试验是确定抗拉强度的巴西试验，确定约束为零的单轴压缩强度的单轴试验，以及确定约束条件下的剪切强度的三轴试验。几十年来，剪切强度的结果被认为是确定岩石破坏包络的最重要的试验。 现在人们普遍认为，完整岩石的抗拉强度是控制完整岩石最终行为的一种基本材料特性。广泛应用的Hoek-Brown经验破坏准则是一种基于岩石三轴压缩破坏的剪切准则。该准则的参数是从室内压缩试验中得出的。初步结果表明，当仅用剪切强度作为输入时，Hoek-Brown不足以预测抗拉区的强度。在这项提案中，我们计划开发一种受限拉力测试，用于跟踪完整岩石从拉伸到压缩的行为。这些试验的结果将被用作修改Hoek-Brown准则的基础，用于那些拉应力可能主导破坏过程的条件。 大型岩质边坡的稳定性主要取决于岩体的内聚力。这种凝聚力可以被拉应力破坏，拉应力是由完整的岩石和岩体的天然非均质性造成的。以抗拉强度为指标，可以有效地量化岩石粘聚力的大小。粘聚力的另一个指标是抗压强度与抗拉强度的比率，该指标用于Hoek-Brown标准。最近的研究表明，这一比例实际上是一种物质属性。对于各种均质和各向异性的岩石，将使用侧向拉伸试验来编制这一比率。一个新开发的利用这一比率作为输入参数的斜坡稳定性数值程序将用于评估几个难以评估斜坡稳定性的实例。这些案例有大量的文件，传统分析的结果不能充分解释他们的行为。实验室测试结果，结合新开发的斜坡模型和实例，将为应用这一方法评估岩质斜坡的稳定性和变形行为提供指导。 研究结果将为采矿业和民用行业制定节理岩体边坡开挖的合理设计方法提供依据。

The initiation and propagation of failure in rock is a matter of fundamental importance in rock engineering. In order to understand the characteristics of rock and rock masses as engineering materials, it is necessary to start with the behaviour of intact rock. From an engineering point of view, this involves studying laboratory scale samples, such as diamond drill core, with dimensions in the range of 50 mm in diameter. For many rock types, the grain size is small enough that samples of this scale can be considered representative of larger intact rock volumes. When establishing the intact strength of rock, several laboratory tests are employed. The more common tests are the Brazilian test to establish the tensile strength, the uniaxial test to establish the uniaxial compressive strength when confinement is zero, and the triaxial test to establish the shear strength under confined conditions. For decades, the results from shear strength were considered the most important tests in establishing the failure envelope for rock. It is now accepted that the tensile strength of intact rock is a fundamental material property that controls the ultimate behaviour of intact rock. The widely used Hoek-Brown empirical failure criterion is a shear criterion based on the triaxial compressive failure of rock. The parameters for the criterion are derived from laboratory compression tests. Preliminary results show that the Hoek-Brown is not adequate for predicting the strength in the tensile region when only the shear strength is used as input. In this proposal, we plan to develop a confined-tension test that will be used to track the behaviour of the intact rock from tension to compression. The results from those tests will be used as the bases for modifying the Hoek-Brown criterion for those conditions where tensile stresses can dominate the failure process. The stability of large rock slopes is dominated by the cohesion of the rock mass. This cohesion can be destroyed by tensile stresses, which are created by the natural heterogeneity of the intact rock and rock mass. Quantifying the magnitude of the rock cohesion can be effectively carried out using the tensile strength as a proxy. Another proxy for cohesion is the ratio of the compressive strength to the tensile strength, and this proxy is used in the Hoek-Brown criteria. Recent research suggests that this ratio is in fact a material property. The confined tension tests will be used to compile this ratio for various homogeneous and anisotropic rocks. A newly developed slope stability numerical program that utilises this ratio as an input parameter will be used to evaluate several case histories where the stability of the slope has been difficult to assess. These case histories have extensive documentation, and the results from traditional analyses have not provided adequate explanations of their behaviour. The laboratory test results, in combination with the newly developed slope model and case histories will provide guidance on the application of this methodology for assessing the stability and deformation behaviour of rock slopes. The results from this research will enable both mining and civil industries to develop rational design approaches for slope excavations in jointed rock masses.