Behaviour of sparsely fractured rock in low confining stresses

岩石破坏的起裂和扩展是岩石工程中的一个重要问题。为了理解岩石和岩体作为工程材料的特性，有必要从完整岩石的行为开始。从工程的角度来看，这包括研究实验室规模的样品，例如直径在50毫米范围内的金刚石钻芯。对于许多岩石类型，颗粒尺寸足够小，这种尺度的样品可以被认为是更大的完整岩石体积的代表。**在建立岩石的完整强度时，采用了几个实验室试验。较常见的试验是建立抗拉强度的巴西试验，建立约束为零时的单轴抗压强度的单轴试验，以及建立约束条件下的三轴抗剪强度的试验。几十年来，抗剪强度的结果被认为是建立岩石破坏包络线的最重要的测试。* *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基本材料特性。目前广泛应用的Hoek-Brown经验破坏准则是基于岩石三轴压缩破坏的剪切准则。该准则的参数来自实验室压缩试验。初步结果表明，当仅以抗剪强度作为输入时，Hoek-Brown法不能很好地预测抗拉区强度。在本提案中，我们计划开发一种围拉试验，用于跟踪完整岩石从拉伸到压缩的行为。这些试验的结果将作为修改Hoek-Brown准则的基础，以适应拉应力可能主导破坏过程的情况。**大型岩质边坡的稳定性主要由岩体的内聚力决定。这种凝聚力可以被拉应力破坏，拉应力是由完整岩石和岩体的自然非均质性产生的。以抗拉强度为指标，可以有效地量化岩石黏聚力的大小。内聚力的另一个代表是抗压强度与抗拉强度的比值，这个代表在Hoek-Brown准则中使用。最近的研究表明，这个比例实际上是一种材料特性。约束拉伸试验将用于编制各种均质和各向异性岩石的这一比率。一个新开发的边坡稳定性数值程序，利用这一比率作为输入参数，将用于评估几个案例的历史，其中边坡的稳定性已难以评估。这些病例有大量的文献记录，传统分析的结果并不能充分解释其行为。实验室测试结果，结合新开发的边坡模型和案例历史，将为应用该方法评估岩石边坡的稳定性和变形行为提供指导。* *这项研究的结果将使采矿和民用工业能够制定节理岩体边坡开挖的合理设计方法。

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.