1.1 这些试验方法包括测定解吸（干燥）的土壤-水特性曲线（SWCC）。SWCC描述了吸力与体积含水量、重量含水量或含水饱和度之间的关系。SWCC也称为土壤水分保持曲线、土壤水分释放曲线或毛管压力曲线。 1.2 本标准描述了确定土壤水分特征曲线的五种方法（A-E）。方法A（悬挂柱）适用于在0至80 kPa范围内测定吸液。方法B（带容积测量的压力室）和方法C（带重量测量的压力室）适用于0至1500 kPa范围内的抽吸。 方法D（冷镜湿度计）适用于测定500 kPa至100 MPa范围内的吸液。方法E（离心法）适用于在0至120 kPa范围内进行测定。方法A通常用于具有少量细粒且易于排水的粗土。方法B和C通常用于更细的土壤，其保持水更紧密。当不需要接近饱和的吸力时，使用方法D，通常用于定义土壤水分特征曲线的干端（即，对应于吸力>1000 kPa的含水量）。方法E通常用于较粗糙的土壤，其中可通过高达120 kPa的吸力提取大量水。 可以将这些方法结合起来，以提供土壤-水特征曲线的详细描述。在本应用中，方法A或E用于定义接近饱和的较低吸力（A为0至80 kPa，E为0至120 kPa）下的土壤水特性曲线，并准确识别进气吸力，方法B或C用于定义中等含水量和吸力（100至1000 kPa）的土壤水特性曲线，方法D用于定义低含水量和高吸力（>1000 kPa）下的土壤水分特征曲线。 1.3 所有观察值和计算值应符合实践中制定的有效数字和舍入指南 D6026 . 实践中的程序 D6026 用于指定如何收集、记录和计算数据的标准被视为行业标准。此外，它们代表了通常应保留的有效数字。这些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。增加或减少报告数据的有效位数以符合这些考虑是常见做法。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。 1.4 单位- 以国际单位制表示的数值应视为标准值。 本标准不包括其他计量单位。 1.5 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 土壤水分特征曲线（SWCC）是非饱和土壤水文特性的基础，也是大多数非饱和土壤水分运动分析所必需的。SWCC还用于表征非饱和土的抗剪强度和压缩性。土壤的非饱和导水率通常使用SWCC和饱和导水率的特性进行估计。 5.2 该方法仅适用于含有两种孔隙流体的土壤:气体和液体。液体通常是水，气体通常是空气。也可以使用其他液体，但如果使用的液体导致土壤基质过度收缩或膨胀，则必须小心。 5.3 尚未对使用该方法获得的土壤水分特征曲线与原位材料的土壤水分特征曲线之间的相关性进行全面调查。因此，应由合格人员谨慎地将该方法获得的结果应用于现场情况。 注1: 本标准产生的结果的质量取决于执行测试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、抽样、检查等。本标准的用户应注意遵守惯例 D3740 本身不能确保可靠的结果。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 These test methods cover the determination of soil water characteristic curves (SWCCs) for desorption (drying). SWCCs describe the relationship between suction and volumetric water content, gravimetric water content, or degree of water saturation. SWCCs are also referred to as soil water retention curves, soil water release curves, or capillary pressure curves. 1.2 This standard describes five methods (A-E) for determining the soil water characteristic curve. Method A (hanging column) is suitable for making determinations for suctions in the range of 0 to 80 kPa. Method B (pressure chamber with volumetric measurement) and Method C (pressure chamber with gravimetric measurement) are suitable for suctions in the range of 0 to 1500 kPa. Method D (chilled mirror hygrometer) is suitable for making determinations for suctions in the range of 500 kPa to 100 MPa. Method E (centrifuge method) is suitable for making determinations in the range 0 to 120 kPa. Method A typically is used for coarse soils with little fines that drain readily. Methods B and C typically are used for finer soils, which retain water more tightly. Method D is used when suctions near saturation are not required and commonly is employed to define the dry end of the soil water characteristic curve (that is, water contents corresponding to suctions >1000 kPa). Method E is typically used for coarser soils where an appreciable amount of water can be extracted with suctions up to 120 kPa. The methods may be combined to provide a detailed description of the soil water characteristic curve. In this application, Method A or E is used to define the soil water characteristic curve at lower suctions (0 to 80 kPa for A, 0 to 120 kPa for E) near saturation and to accurately identify the air entry suction, Method B or C is used to define the soil water characteristic curve for intermediate water contents and suctions (100 to 1000 kPa), and Method D is used to define the soil water characteristic curves at low water contents and higher suctions (>1000 kPa). 1.3 All observed and calculated values shall conform to the guide for significant digits and rounding established in Practice D6026 . The procedures in Practice D6026 that are used to specify how data are collected, recorded, and calculated are regarded as the industry standard. In addition, they are representative of the significant digits that should generally be retained. The procedures do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the objectives of the user. Increasing or reducing the significant digits of reported data to be commensurate with these considerations is common practice. Consideration of the significant digits to be used in analysis methods for engineering design is beyond the scope of this standard. 1.4 Units— The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.5 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 The soil water characteristic curve (SWCC) is fundamental to hydrological characterization of unsaturated soils and is required for most analyses of water movement in unsaturated soils. The SWCC is also used in characterizing the shear strength and compressibility of unsaturated soils. The unsaturated hydraulic conductivity of soil is often estimated using properties of the SWCC and the saturated hydraulic conductivity. 5.2 This method applies only to soils containing two pore fluids: a gas and a liquid. The liquid is usually water and the gas is usually air. Other liquids may also be used, but caution must be exercised if the liquid being used causes excessive shrinkage or swelling of the soil matrix. 5.3 A full investigation has not been conducted regarding the correlation between soil water characteristic curves obtained using this method and soil water characteristics curves of in-place materials. Thus, results obtained from this method should be applied to field situations with caution and by qualified personnel. Note 1: The quality of the result produced by this standard depends on the competence of the personnel performing the test 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, etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself ensure reliable results. Reliable results depend on many factors. Practice D3740 provides a means of evaluating some of these factors.