1.1 本试验方法确定了在恒定法向载荷下对岩石试样进行直接剪切强度试验的要求和实验室程序。它包括完整岩石强度和滑动摩擦试验的程序，可在均质或具有软弱面（包括自然或人工不连续）的试样上进行。人工不连续的例子包括岩石-混凝土界面或混凝土浇筑的提升线。不连续可能是开放的、部分或完全愈合或填充的（即粘土填充物和凿槽）。每个试样只能测试一个不连续性。试验通常在不排水状态下进行，并施加恒定的正常载荷。然而，清洁、开放的不连续性可能是自由排水的，因此，对清洁、开放的不连续性进行的试验可被视为排水试验。 在试验过程中，在垂直于剪切面的各种施加应力和各种剪切位移下测定剪切强度。从试验数据得出的关系包括剪切强度与法向应力以及剪切应力与剪切位移（剪切刚度）。 注1: 标题中使用了术语“法向力”，而不是法向应力，因为在测试过程中，接触面积不可定义，试样上下半部分之间的相对位移最小。测试期间的实际接触面积发生变化，但实际总接触面无法测量。因此，标称面积用于加载和计算。 注2: 由于本试验方法未规定孔隙压力的测量，因此测定的强度值以总应力表示，未校正孔隙压力。 1.2 本标准适用于硬岩、中岩、软岩和混凝土。 1.3 本试验方法仅适用于在恒定法向载荷边界条件下单调剪切下的岩石或混凝土试样的准静态试验。恒定法向载荷边界条件适用于法向应力沿不连续面恒定的问题。恒定法向载荷边界条件可能不适用于剪胀控制的问题，并且法向应力沿不连续面不是恒定的。 1.4 所有观察值和计算值应符合实践中确定的有效数字和舍入准则 D6026 . 1.4.1 本标准中用于规定如何收集/记录和计算数据的程序被视为行业标准。 此外，它们代表了通常应保留的有效数字。使用的程序不考虑材料变化、获取数据的目的、特殊目的研究或用户目标的任何考虑因素；通常的做法是增加或减少报告数据的有效位数，以与这些考虑因素相称。考虑工程设计分析方法中使用的有效数字超出了这些测试方法的范围 1.5 单位- 以国际单位制表示的数值应视为标准值。括号中给出的值是英寸-磅单位的数学转换，仅供参考，不被视为标准值。以国际单位制以外的单位报告试验结果不应视为不符合本试验方法。 1.6 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全和健康实践，并确定监管限制的适用性。 ====意义和用途====== 5.1 岩石样本抗剪强度的确定是岩石边坡、坝基、隧道、竖井、废物储存库、储存洞室等结构设计中的一个重要方面。岩体中普遍存在的不连续性（节理、层理面、剪切带、断层带、片理）以及成因、结晶学、纹理、组构和其他因素可能导致岩体表现为各向异性和非均质不连续。 因此，很难精确预测岩体行为。 5.2 对于非平面节理或不连续性，剪切强度来自基材摩擦和微凸体覆盖（扩容）、微凸体剪切或断裂以及微凸体旋转或楔入的组合。微凸体的滑动和剪切可以同时发生。当法向力不足以抑制膨胀时，剪切机制包括覆盖微凸体。当法向载荷大到足以完全抑制膨胀时，剪切机制包括剪切微凸体。 5.3 使用该试验方法确定完整试样的剪切强度可能会产生翻转力矩，从而导致倾斜剪切断裂。 5.4 抗剪强度受覆盖层或正常压力的影响；因此，表土压力越大，抗剪强度越大。 5.5 在某些情况下，可能需要在现场而不是实验室进行测试，以确定岩体的代表性抗剪强度，特别是当设计由填充非常弱材料的不连续性控制时。现场直剪试验限制了岩石力学问题中发现的固有比例效应，其中实验室规模可能无法代表现场规模。 5.6 从获得样本到测试样本的处理方式对结果有很大影响。因此，可能有必要按照惯例处理样本 D5079 并在数据收集中以某种方式记录水分条件。 注3: 本标准产生的结果的质量取决于执行该标准的人员的能力，以及所用设备和设施的适用性。符合实践标准的机构 D3740 通常认为能够胜任和客观的测试/采样/检查等。本标准的用户应注意遵守惯例 D3740 本身并不能保证可靠的结果。可靠的结果取决于许多因素，实践 D3740 提供了一种评估其中一些因素的方法。

1.1 This test method establishes requirements and laboratory procedures for performing direct shear strength tests on rock specimens under a constant normal load. It includes procedures for both intact rock strength and sliding friction tests, which can be performed on specimens that are homogeneous, or have planes of weakness, including natural or artificial discontinuities. Examples of an artificial discontinuity include a rock-concrete interface or a lift line from a concrete pour. Discontinuities may be open, partially or completely healed or filled (that is, clay fillings and gouge). Only one discontinuity per specimen can be tested. The test is usually conducted in the undrained state with an applied constant normal load. However, a clean, open discontinuity may be free draining, and, therefore, a test on a clean, open discontinuity could be considered a drained test. During the test, shear strength is determined at various applied stresses normal to the sheared plane and at various shear displacements. Relationships derived from the test data include shear strength versus normal stress and shear stress versus shear displacement (shear stiffness). Note 1: The term “normal force” is used in the title instead of normal stress because of the indefinable area of contact and the minimal relative displacement between upper and lower halves of the specimen during testing. The actual contact areas during testing change, but the actual total contact surface is unmeasurable. Therefore nominal area is used for loading purposes and calculations. Note 2: Since this test method makes no provision for the measurement of pore pressures, the strength values determined are expressed in terms of total stress, uncorrected for pore pressure. 1.2 This standard applies to hard rock, medium rock, soft rock, and concrete. 1.3 This test method is only applicable to quasi-static testing of rock or concrete specimens under monotonic shearing with a constant normal load boundary condition. The constant normal load boundary condition is appropriate for problems where the normal stress is constant along the discontinuity. The constant normal load boundary condition may not be appropriate for problems where shearing is dilatancy controlled and the normal stress is not constant along the discontinuity. 1.4 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026 . 1.4.1 The procedures used to specify how data are collected/recorded and calculated in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported data to commensurate with these considerations. It is beyond the scope of these test methods to consider significant digits used in analysis methods for engineering design 1.5 Units— The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units, which are provided for information only and are not considered standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this test method. 1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. ====== Significance And Use ====== 5.1 Determination of shear strength of a rock specimen is an important aspect in the design of structures such as rock slopes, dam foundations, tunnels, shafts, waste repositories, caverns for storage, and other purposes. Pervasive discontinuities (joints, bedding planes, shear zones, fault zones, schistosity) in a rock mass, and genesis, crystallography, texture, fabric, and other factors can cause the rock mass to behave as an anisotropic and heterogeneous discontinuum. Therefore, the precise prediction of rock mass behavior is difficult. 5.2 For nonplanar joints or discontinuities, shear strength is derived from a combination base material friction and overriding of asperities (dilatancy), shearing or breaking of the asperities, and rotations at or wedging of the asperities. Sliding on and shearing of the asperities can occur simultaneously. When the normal force is not sufficient to restrain dilation, the shear mechanism consists of the overriding of the asperities. When the normal load is large enough to completely restrain dilation, the shear mechanism consists of the shearing off of the asperities. 5.3 Using this test method to determine the shear strength of an intact specimen may generate overturning moments which could result in an inclined shear break. 5.4 Shear strength is influenced by the overburden or normal pressure; therefore, the larger the overburden pressure, the larger the shear strength. 5.5 In some cases, it may be desirable to conduct tests in situ rather than in the laboratory to determine the representative shear strength of the rock mass, particularly when design is controlled by discontinuities filled with very weak material. In situ direct shear testing limits the inherent scale effects found in rock mechanics problems where the laboratory scale may not be representative of the field scale. 5.6 The results can be highly influenced by how the specimen is treated from the time it is obtained until the time it is tested. Therefore, it may be necessary to handle specimens in accordance with Practice D5079 and to document moisture conditions in some manner in the data collection. Note 3: The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection and the like. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors, Practice D3740 provides a means of evaluating some of those factors.