1.1 本试验方法将实验室滤纸作为被动传感器，用于评估土壤基质和总电位（吸力），这是一种测量孔隙水自由能或土壤基质施加在孔隙水上的张力的方法 ( 1. , 2. ) . 2. 势或吸力一词描述土壤水的能量状态。 1.2 本试验方法控制测量滤纸含水量的变量，滤纸与土壤直接接触，或与封闭土壤样本的密闭容器空气中的水蒸气分压平衡。 滤纸与密闭容器中的土壤样本一起密封，直到建立水分平衡；也就是说，空气中的水汽分压与土壤样本中孔隙水的蒸汽压平衡。 1.3 本试验方法提供了一种校准不同类型滤纸的程序，用于评估土壤基质和总电位。 1.4 单位- 以国际单位制表示的数值应视为标准值。括号中给出的英寸-磅单位是数学转换，仅供参考，不被视为标准。 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 土壤吸力是土壤中孔隙水自由能的测量值。实际上，土壤吸力是土壤保持水分亲和力的一种度量，可以提供受土壤水分影响的土壤参数信息； 例如，土壤的体积变化、变形和强度特征。 5.2 土壤吸力通过保水特性曲线与土壤含水量相关（见试验方法 D6836 ). 土壤含水量可使用试验方法测定 D2216 . 5.3 土壤吸力测量可与其他土壤和环境参数一起用于评估水文过程 ( 1. ) 并评估非饱和土的隆起或收缩、抗剪强度、模量、地应力和导水率的可能性。 5.4 评估吸力的滤纸方法很简单，范围为10至100000 kPa（0。 1至1000巴）。 注1: 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 This test method covers laboratory filter papers as passive sensors to evaluate the soil matric and total potential (suction), a measure of the free energy of the pore-water or tension stress exerted on the pore-water by the soil matrix ( 1 , 2 ) . 2 The term potential or suction is descriptive of the energy status of soil water. 1.2 This test method controls the variables for measurement of the water content of filter paper that is in direct contact with soil or in equilibrium with the partial pressure of water vapor in the air of an airtight container enclosing a soil specimen. The filter paper is enclosed with a soil specimen in the airtight container until moisture equilibrium is established; that is, the partial pressure of water vapor in the air is in equilibrium with the vapor pressure of pore-water in the soil specimen. 1.3 This test method provides a procedure for calibrating different types of filter paper for use in evaluating soil matric and total potential. 1.4 Units— The values stated in SI units are to be regarded as standard. The inch-pound units given in parentheses are mathematical conversions, which are provided for information purposes only and are not considered 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 Soil suction is a measure of the free energy of the pore-water in a soil. Soil suction in practical terms is a measure of the affinity of soil to retain water and can provide information on soil parameters that are influenced by the soil water; for example, volume change, deformation, and strength characteristics of the soil. 5.2 Soil suction is related with soil water content through water retention characteristic curves (see Test Methods D6836 ). Soil water content may be determined using Test Method D2216 . 5.3 Measurements of soil suction may be used with other soil and environmental parameters to evaluate hydrologic processes ( 1 ) and to evaluate the potential for heave or shrinkage, shear strength, modulus, in situ stress and hydraulic conductivity of unsaturated soils. 5.4 The filter paper method of evaluating suction is straightforward with a range from 10 to 100,000 kPa (0.1 to 1000 bars). Note 1: 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/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 those factors.