1.1 该试验方法用于使用连续控制应变轴向压缩测定饱和粘性土的固结程度和速率。试样横向约束，轴向排水至一个表面。在变形过程中测量轴向力和基底超压。受控应变压缩通常被称为恒定应变率（CRS）测试。 1.2 该试验方法通过测量轴向力、轴向变形、腔室压力和基座超压来计算总轴向应力和有效轴向应力以及轴向应变。使用稳态方程计算有效应力。 1.3 该试验方法用于计算整个加载过程中的固结系数和导水率。 这些值也是基于稳态方程。 1.4 这种测试方法利用了在特定假设下形成的理论所产生的稳态方程。小节 5.5 提出了这些假设。 1.5 粘性土的行为与应变速率有关，因此CRS试验的结果对施加的应变速率很敏感。该试验方法对应变速率进行了限制，以提供与增量固结试验（试验方法 D2435 ). 1.6 当土壤受到增量荷载时，土壤固结速率和大小的测定包括在试验方法中 D2435 . 1.7 此测试方法适用于完整的（实践的C组和D组 D4220 )、重塑或实验室重建的样品。 1.8 这种测试方法最常用于水力传导率相对较低的材料，这些材料会产生可测量的过量基础压力。它可以用于测量基本上自由排水的土壤的压缩行为，但不会提供水力传导率或固结系数的测量。 1.9 所有记录和计算的值应符合实践中制定的有效数字和舍入指南 D6026 ，除非被本试验方法取代。本标准中规定的有效数字基于这样一种假设，即数据将在从最大应力的1%到最大应力值的轴向应力范围内收集。 1.9.1 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。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本标准的范围。 1.9.2 对超过本标准规定的有效数字或灵敏度的测量不应视为不符合本标准。 1.10 单位-- 以国际单位制或英寸磅单位[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。将两个系统的值合并可能导致不符合标准。以SI以外的单位报告试验结果不应被视为不符合本标准。 1.10.1 在使用英寸磅单位时使用重力系统。在这个系统中，磅（lbf）表示力（重量）的单位，而质量的单位是蛞蝓。除非是动态的，否则不会给出合理的段塞单元( F =ma）计算。 1.10.2 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）。 这隐含地结合了两个独立的单位系统；即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，本标准包括以英寸-磅为单位的重力系统，不使用/表示段塞质量单位。但是，使用天平或天平记录质量磅（lbm）或以lbm/ft为单位记录密度 3. 不应被视为不符合本标准。 1.11 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。 1.12 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 在土结构和土支撑结构的设计中，有关土壤压缩程度和固结率的信息至关重要。该试验方法的结果可用于分析或估计一维沉降、与多余孔隙水压力消散相关的沉降速率以及由于水力梯度引起的流体传输速率。 此测试方法未提供有关二次压缩率的信息。 5.2 应变率效应: 5.2.1 固结试验的应力-应变结果与应变速率有关。在该试验方法中，应变速率受到加载阶段基础超压比可接受大小规范的限制。本规范提供了与使用试验方法获得的100%固结（主压缩结束）压缩性能相当的结果 D2435 . 5.2.2 场应变率随时间、加载区域下方的深度以及与加载区域的径向距离变化很大。固结过程中的现场应变速率通常比实验室应变速率慢得多，并且无法准确确定或预测。 由于这些原因，将现场应变速率与实验室测试应变速率进行复制是不现实的。 5.3 温度影响: 5.3.1 温度会影响速率参数，如导水率和固结系数。温度效应的主要原因是孔隙流体粘度的变化，但土壤敏感性也可能很重要。该测试方法提供了室温条件下的结果，可能需要对特定的现场条件进行校正。此类修正超出了本试验方法的范围。可以进行特殊调整，以复制现场温度条件，并且仍然符合该测试方法。 5.4 饱和效果: 5.4.1 该试验方法不能用于测量部分饱和土壤的性质，因为该方法要求材料在固结前进行背压饱和。 5.5 测试解释假设-- 本试验方法中使用的方程式基于以下假设: 5.5.1 土壤已饱和。 5.5.2 土壤是均匀的。 5.5.3 土壤颗粒和水的压缩性可以忽略不计。 5.5.4 孔隙水仅在垂直方向上流动。 5.5.5 达西渗流定律适用于多孔介质。 5.5.6 在各个读数集之间的时间间隔内，整个样本的土壤导水率与压缩率之比是恒定的。 5.5.7 与土壤的压缩性相比，基础超压测量系统的压缩性可以忽略不计。 5.6 理论解决方案: 5.6.1 恒定应变固结率的解可用于线性和非线性土壤模型。 5.6.1.1 线性模型假设土壤具有恒定的体积压缩系数( m v ). 这些方程如所示 13.4 . 5.6.1.2 非线性模型假设土壤具有恒定的压缩指数( C c ). 这些方程如所示 附录X1 . 注2: 假设在试样边界处测得的基础超压等于试样中的最大超孔隙水压力。整个样本中多余孔隙水压力的分布是未知的。每个模型预测不同的分布。随着基础超压的大小增加，两个模型预测之间的差异也会增加。 在15%的基本超压比下，两个模型之间的平均有效应力计算差异约为0.3%。 5.6.2 线性情况下的方程用于该测试方法。该测试方法将读数和最大基准超压比之间的时间间隔限制为使用任一理论时产生类似结果的值。但是，更精确的做法是使用与压缩曲线形状最匹配的模型。 5.6.3 非线性方程在中给出 附录X1 并且它们的使用不被视为不符合该测试方法。 5.6.4 本试验方法中使用的方程式仅适用于稳态条件。在稳态因子之后，加载或卸载阶段开始时的瞬态应变分布是不显著的( F )超过0.4。本试验方法中未使用与较低稳态因子相对应的数据。 5.7 该试验方法可用于测量自由排水土壤的压缩特性。对于此类材料，基底超压将为零，因此无法计算固结系数或导水系数。在这种情况下，平均有效轴向应力等于总轴向应力，结果与模型无关。 5.8 本试验方法中提出的程序假设在基础压力测量系统中使用高渗透性多孔圆盘。使用低渗透性多孔圆盘或高空气进入（>1巴）圆盘将需要修改设备规范和程序。 这些修改超出了本测试方法的范围，不被视为不合格。 注3: 应用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设备和设施的适用性。符合实践标准的机构 D3740 通常被认为有能力进行合格和客观的测试/取样/检查等。本标准的用户应注意遵守实践 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 is for the determination of the magnitude and rate-of-consolidation of saturated cohesive soils using continuous controlled-strain axial compression. The specimen is restrained laterally and drained axially to one surface. The axial force and base excess pressure are measured during the deformation process. Controlled strain compression is typically referred to as constant rate-of-strain (CRS) testing. 1.2 This test method provides for the calculation of total and effective axial stresses, and axial strain from the measurement of axial force, axial deformation, chamber pressure, and base excess pressure. The effective stress is computed using steady state equations. 1.3 This test method provides for the calculation of the coefficient of consolidation and the hydraulic conductivity throughout the loading process. These values are also based on steady state equations. 1.4 This test method makes use of steady state equations resulting from a theory formulated under particular assumptions. Subsection 5.5 presents these assumptions. 1.5 The behavior of cohesive soils is strain rate dependent and hence the results of a CRS test are sensitive to the imposed rate of strain. This test method imposes limits on the strain rate to provide comparable results to the incremental consolidation test (Test Method D2435 ). 1.6 The determination of the rate and magnitude of consolidation of soil when it is subjected to incremental loading is covered by Test Method D2435 . 1.7 This test method applies to intact (Group C and Group D of Practice D4220 ), remolded, or laboratory reconstituted samples. 1.8 This test method is most often used for materials of relatively low hydraulic conductivity that generate measurable excess base pressures. It may be used to measure the compression behavior of essentially free draining soils but will not provide a measure of the hydraulic conductivity or coefficient of consolidation. 1.9 All recorded and calculated values shall conform to the guide for significant digits and rounding established in Practice D6026 , unless superseded by this test method. The significant digits specified throughout this standard are based on the assumption that data will be collected over an axial stress range from 1% of the maximum stress to the maximum stress value. 1.9.1 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 should generally 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 this standard to consider significant digits used in analysis methods for engineering design. 1.9.2 Measurements made to more significant digits or better sensitivity than specified in this standard shall not be regarded a non-conformance with this standard. 1.10 Units— The values stated in either SI units or inch-pound 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 non-conformance with the standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this standard. 1.10.1 The gravitational system is used when working with inch-pound units. In this system, the pound (lbf) represents a unit of force (weight), while the unit for mass is slugs. The rationalized slug unit is not given, unless dynamic ( F = ma) calculations are involved. 1.10.2 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 implicitly combines two separate systems of units; that is, the absolute system and the gravitational system. 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 for mass. However, the use of balances or scales recording pounds of mass (lbm) or recording density in lbm/ft 3 shall not be regarded as non-conformance with this standard. 1.11 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. 1.12 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 Information concerning magnitude of compression and rate-of-consolidation of soil is essential in the design of earth structures and earth supported structures. The results of this test method may be used to analyze or estimate one-dimensional settlements, rates of settlement associated with the dissipation of excess pore-water pressure, and rates of fluid transport due to hydraulic gradients. This test method does not provide information concerning the rate of secondary compression. 5.2 Strain Rate Effects: 5.2.1 It is recognized that the stress-strain results of consolidation tests are strain rate dependent. Strain rates are limited in this test method by specification of the acceptable magnitudes of the base excess pressure ratio during the loading phase. This specification provides comparable results to the 100 % consolidation (end of primary) compression behavior obtained using Test Method D2435 . 5.2.2 Field strain rates vary greatly with time, depth below the loaded area, and radial distance from the loaded area. Field strain rates during consolidation processes are generally much slower than laboratory strain rates and cannot be accurately determined or predicted. For these reasons, it is not practical to replicate the field strain rates with the laboratory test strain rate. 5.3 Temperature Effects: 5.3.1 Temperature affects the rate parameters such as hydraulic conductivity and the coefficient of consolidation. The primary cause of temperature effects is due to the changes in pore fluid viscosity, but soil sensitivity may also be important. This test method provides results under room temperature conditions, corrections may be required to account for specific field conditions. Such corrections are beyond the scope of this test method. Special accommodation may be made to replicate field temperature conditions and still be in conformance with this test method. 5.4 Saturation Effects: 5.4.1 This test method may not be used to measure the properties of partially saturated soils because the method requires the material to be back pressure saturated prior to consolidation. 5.5 Test Interpretation Assumptions— The equations used in this test method are based on the following assumptions: 5.5.1 The soil is saturated. 5.5.2 The soil is homogeneous. 5.5.3 The compressibility of the soil particles and water is negligible. 5.5.4 Flow of pore water occurs only in the vertical direction. 5.5.5 Darcy's law for flow through porous media applies. 5.5.6 The ratio of soil hydraulic conductivity to compressibility is constant throughout the specimen during the time interval between individual reading sets. 5.5.7 The compressibility of the base excess pressure measurement system is negligible compared to that of the soil. 5.6 Theoretical Solutions: 5.6.1 Solutions for constant rate of strain consolidation are available for both linear and nonlinear soil models. 5.6.1.1 The linear model assumes that the soil has a constant coefficient of volume compressibility ( m v ). These equations are presented in 13.4 . 5.6.1.2 The nonlinear model assumes that the soil has a constant compression index ( C c ). These equations are presented in Appendix X1 . Note 2: The base excess pressure measured at the boundary of the specimen is assumed equal to the maximum excess pore-water pressure in the specimen. The distribution of excess pore-water pressure throughout the specimen is unknown. Each model predicts a different distribution. As the magnitude of the base excess pressure increases, the difference between the two model predictions increases. At a base excess pressure ratio of 15 %, the difference in the average effective stress calculation between the two models is about 0.3 %. 5.6.2 The equations for the linear case are used for this test method. This test method limits the time interval between readings and the maximum base excess pressure ratio to values that yield similar results when using either theory. However, it is more precise to use the model that most closely matches the shape to the compression curve. 5.6.3 The nonlinear equations are presented in Appendix X1 and their use is not considered a non-conformance with this test method. 5.6.4 The equations used in this test method apply only to steady state conditions. The transient strain distribution at the start of a loading or unloading phase is insignificant after the steady state factor ( F ) exceeds 0.4. Data corresponding to lower steady state factors are not used in this test method. 5.7 This test method may be used to measure the compression behavior of free draining soils. For such materials, the base excess pressure will be zero and it will not be possible to compute the coefficient of consolidation or the hydraulic conductivity. In this case, the average effective axial stress is equal to the total axial stress and the results are independent of model. 5.8 The procedures presented in this test method assume a high permeability porous disk is used in the base pressure measurement system. Use of a low permeability porous disk or high-air entry (>1 bar) disk will require modification of the equipment specifications and procedures. These modifications are beyond the scope of this test method and are not considered a non-conformance. Note 3: The quality of the results produced by application of this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. 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.