1.1 本试验方法包括在直接剪切边界条件下测定一个土壤材料试样的固结排水抗剪强度。试样在由设备配置确定的单个剪切平面上或附近以受控速率变形。 1.2 剪切应力和位移在试样内分布不均匀。不能为剪切应变的计算定义适当的破坏区高度。因此，应力-应变关系或任何相关的量，如剪切模量，不能从该试验中确定。 1.3 测试结果受到粗粒土壤或岩石颗粒的影响，或两者兼而有之，在某些情况下，这可能会使测试数据无效。 检查6.2.1和6.2.2中最大土壤粒径的要求。 1.4 应选择试验条件，包括正应力、固结和剪切过程中的水通道以及试样条件，以代表正在调查的现场条件，并将其留给要求进行试验的工程师或办公室。剪切速率必须足够慢，以确保排水条件。 1.5 通常，对一个土样的试样进行三次或三次以上的试验，每次试验都在不同的法向荷载下进行，以确定对抗剪性和位移的影响。解释和评估测试结果的标准的制定由要求测试的工程师或办公室负责。多次试验的解释需要工程判断，超出了本试验方法的范围。 此测试方法适用于单个测试的要求。 1.6 该试验方法根据剪切盒的尺寸限制试样的最大粒径。同样，规定了剪切过程中的间隙尺寸。测试请求者可以要求剪切箱上下半部之间有一定的间隙尺寸，以容纳特定尺寸的砂粒。目前，没有足够的信息可用于基于粒度分布指定间隙尺寸。 1.7 单位-- 以英寸磅单位或国际单位制（括号内给出）表示的数值应单独视为标准。每个系统中规定的值可能不是完全相等的；因此，每个系统应独立使用。 将两个系统的值结合起来可能会导致不符合标准。 1.7.1 处理英寸磅单位时使用英寸磅单位的重力系统。在这个系统中，磅（lbf）表示力（重量）的单位，而质量的单位是弹塞。除非涉及动态（F=ma）计算，否则未给出段塞单元。 1.7.2 工程/建筑行业的常见做法是同时使用磅来表示质量单位（lbm）和力单位（lbf）。这种做法隐含地结合了两个独立的单位系统；绝对系统和引力系统。在一个标准中同时使用两套独立的英寸磅单位在科学上是不可取的。 如前所述，本标准包括英寸磅单位的重力系统，不使用/表示段塞质量单位。但是，使用天平和天平记录磅质量（lbm）或记录密度（lbm/ft） 3. 不得视为不符合本标准。 1.8 所有观测值和计算值应符合实践中制定的有效数字和四舍五入指南 D6026 ，除非被本试验方法取代。 1.8.1 为了将测量或计算值与规定限值进行比较，测量或计算的值应四舍五入至规定限值有效数字的最接近小数点。 1.8.2 用于规定如何在标准中收集/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。所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；并且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。 1.9 本标准并不旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.10 本国际标准是根据世界贸易组织技术性贸易壁垒委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认的标准化原则制定的。 ====意义和用途====== 5.1 直剪试验适用于在固结排水条件下相对快速地确定土壤的排水摩擦角，因为通过试样的排水路径较短，使多余的孔隙压力比其他排水强度试验更快地消散。它适用于测试完整或重构的样本。 但是，最大颗粒尺寸有限制（请参见 6.2.1 和 6.2.2 )。 5.2 测试方案代表了在现有正应力下发生完全固结的现场情况。在排水条件下，破坏缓慢达到，以允许剪切过程中多余的孔隙压力消散。剪切速率必须满足的要求 9.10 几个试验的结果可用于表示破坏面上的法向应力与排水抗剪强度之间的关系。 注1: 本标准方法中规定的设备不适用于进行不排水剪切试验。在没有适当控制试样体积的情况下使用快速位移率将导致局部排水和剪切参数的错误测量。 5.3 在直接剪切试验过程中，主应力发生旋转，并且由于破坏是被迫发生在穿过试样中间的平面上或附近，因此破坏可能不会发生在最弱的平面上。试验中平面的固定位置有利于确定土壤材料内可识别薄弱平面的抗剪性，也有利于测试不同材料之间的界面。 5.4 试验有一些局限性，例如破坏面上剪切应力的不均匀性，以及由于土壤内的不均匀和施加的力（剪切过程中剪切箱上半部向上或向下移动引起的力矩等）而导致破坏面不均匀的可能性。 此外，当测试高度超固结的完整硬粘土时，可能存在裂缝或其他不连续性，导致过度倾斜、剪切时的垂直运动（向上或向下）等，这将使直接剪切测试无效。 5.5 剪切表面的面积在试验过程中减小。这种面积减小在剪切平面上的剪切应力和法向应力的实际值中产生了不确定性，但不应影响这些应力的比率。 注2: 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 通常被认为能够胜任和客观的测试/取样/检查/等等。该试验方法的使用者应注意遵守规程 D3740 其本身不能保证可靠的结果。可靠的结果取决于许多因素；实践 D3740 提供了评估其中一些因素的方法。

1.1 This test method covers the determination of the consolidated drained shear strength of one specimen of a soil material under direct shear boundary conditions. The specimen is deformed at a controlled rate on or near a single shear plane determined by the configuration of the apparatus. 1.2 Shear stresses and displacements are nonuniformly distributed within the specimen. An appropriate height of the failure zone cannot be defined for calculation of shear strains. Therefore, stress-strain relationships or any associated quantity such as the shear modulus, cannot be determined from this test. 1.3 The results of the test are affected by the presence of coarse-grained soil or rock particles, or both, which may make the testing data invalid in some cases. Check requirements of maximum soil particle size in 6.2.1 and 6.2.2. 1.4 Test conditions, including normal stress, access to water during consolidation and shearing, and specimens conditions should be selected to represent the field conditions being investigated and are left to the engineer or office requesting the test. The rate of shearing must be slow enough to ensure drained conditions. 1.5 Generally, three or more tests are performed on specimens from one soil sample, each under a different normal load, to determine the effects upon shear resistance and displacement. The development of criteria to interpret and evaluate test results is left to the engineer or office requesting the test. Interpretation of multiple tests requires engineering judgment and is beyond the scope of this test method. This test method pertains to the requirements for a single test. 1.6 This test method limits the maximum particle size of the test specimen based on the size of the shear box. Likewise, the gap size during shear is specified. It is acceptable for the testing requester to require a certain gap size between the upper and lower shear box halves to accommodate certain sand size particles. Presently there is insufficient information available for specifying the gap dimension based on particle size distribution. 1.7 Units— The values stated in either inch-pound units or SI units [given in brackets] are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard. 1.7.1 The gravitational system of inch-pound units is used when dealing with inch-pound units. In this system, the pound (lbf) represents a unit of force (weight), while the unit for mass is a slug. The slug unit is not given, unless dynamic (F = ma) calculations are involved. 1.7.2 It is common practice in the engineering/construction profession to concurrently use pounds to represent both a unit of mass (lbm) and of force (lbf). This practice implicitly combines two separate systems of units; the absolute and the gravitational systems. It is scientifically undesirable to combine the use of two separate sets of inch-pound units within a single standard. As stated, this standard includes the gravitational system of inch-pound units and does not use/present the slug unit of mass. However, the use of balances and scales recording pounds of mass (lbm) or recording density in lbm/ft 3 shall not be regarded as nonconformance with this standard. 1.8 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026 , unless superseded by this test method. 1.8.1 For purposes of comparing a measured or calculated value(s) with specified limits, the measured or calculated value(s) shall be rounded to the nearest decimal of significant digits in the specified limit. 1.8.2 The procedures used to specify how data are collected/recorded and calculated in the 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 the 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 be commensurate with these considerations. It is beyond the scope of these test methods to consider significant digits used in analysis methods for engineering design. 1.9 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.10 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 The direct shear test is suited to the relatively rapid determination of the drained friction angle of soils under consolidated drained conditions because the drainage paths through the test specimen are short, allowing excess pore pressure to dissipate more rapidly than other drained strength tests. It is applicable for testing intact, or reconstituted specimens. There is, however, a limitation on the maximum particle size (see 6.2.1 and 6.2.2 ). 5.2 The testing protocols represent a field situation where complete consolidation has occurred under the existing normal stresses. Failure is reached slowly under drained conditions to allow excess pore pressure dissipation during shear. The shear rate must meet the requirements of 9.10 . The results from several tests may be used to express the relationship between normal stress on the failure plane and drained shear strength. Note 1: The equipment specified in this standard method is not appropriate for performing undrained shear tests. Using a fast displacement rate without proper control of the volume of the specimen will result in partial drainage and incorrect measurements of shear parameters. 5.3 During the direct shear test, there is rotation of principal stresses and failure may not occur on the weakest plane since failure is forced to occur on or near a plane through the middle of the specimen. The fixed location of the plane in the test can be an advantage in determining the shear resistance along recognizable weak planes within the soil material and for testing interfaces between dissimilar materials. 5.4 There are some limitations of the test, such as nonuniformity of shear stress on the failure plane and possibilities of nonuniformity of the failure plane due to nonuniformities within the soil and applied forces (moments caused by top half of shear box movement either up or down during shearing, and the like). Furthermore, when testing intact stiff clays, which are highly overconsolidated, there might be fissures or other discontinuities to cause excessive tilting, vertical movement (up or down) while shearing, and the like, and which, would nullify the use of the direct shear test. 5.5 The area of the shear surface decreases during the test. This area reduction creates uncertainty in the actual value of the shear and normal stress on the shear plane but should not affect the ratio of these stresses. Note 2: 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 test method 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.