Development of the Constant-Flow Method for Concurrent Measurement of the Soil-Water Characteristic Curve and Hydraulic Conductivity Function of Unsaturated Soils

非饱和土土水特征曲线和导水率函数恒流同步测量方法的研制

• 批准号: 0306823
• 负责人: William Likos
• 金额: $ 4.91万
• 依托单位: University of Missouri-Columbia
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-10-01 至 2004-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0306823&HistoricalAwards=false
• 关键词: Development; Constant; Flow; Method; Concurrent

PI: William LikosInstitution: Colorado School of MinesTitle: "Development of the constant-flow method for concurrent measurement of the soil-water characteristic curve and hydraulic conductivity function of unsaturated soils"Two fundamental material parameters are required to analyze geotechnical and geoenvironmental engineering problems involving the flow of fluids through unsaturated soils:1) the soil-water characteristic curve, and 2) the hydraulic conductivity function. Together, thesefunctions describe the relationships among matric suction, hydraulic conductivity, and water content in unsaturated soils. The functions may either be measured directly or modeled indirectly.Currently, there is a considerable shortage of practical, cost-effective, and reliable experimental techniques for direct measurements of these two important parameters. Several techniques have been developed for independently measuring either the soil-water characteristic curve or the hydraulic conductivity function; however, very few are available for concurrent measurement of both functions, particularly for a single undisturbed specimen under stress-controlled conditions. Most of the existing techniques tend to be impractical for general use because they are limited in terms of complexity and/or cost. As a result, engineers in practice more often rely on indirect estimations of characteristic curves and conductivity functions using analytical or empirical models based on routinely measured material properties such as grain-size. In most situations, however, direct measurements are much more desirable.This research attempts to develop the constant-flow method (CFM) for direct, steady-state, and concurrent measurement of both the soil-water characteristic curve and hydraulic conductivity function of unsaturated soils. The majority of the work will be in the form of modifications to a prototype CFM permeameter system developed in the mid 1990's by project Co-PI Dr. Harold Olsen at the Colorado School of Mines. Early results demonstrated several distinct advantages over the more traditional measurement techniques. Most notably, both functions could be obtained for a single specimen without the requirement for separate testing procedures on split sub-samples. Hydraulic conductivity (HC) measurements could be obtained much more rapidly and with substantially smaller hydraulic gradients. Because testing was conducted in a triaxial cell, HC and matric suction could be evaluated as functions of water content as well as applied effective stress. Unfortunately, several limitations were also evident in the prototype CFM system. Specifically, HC measurements were limited to relatively fine-grained soils (k 10 -8 cm/sec), pore-air pressure was applied at only one end of the specimen, diffused-air flushing circuits were not incorporated, specimen volume changes could not be measured, and problems with leakage due to an overly complex design were encountered.The primary goal of this work is to expand the capability and practicality of the CFM approach for unsaturated soils testing by addressing and eliminating these limitations. Key modifications to the prototype system will allow HC to be measured for both coarse- and fine-grained soils, account for specimen volume change, decrease testing time, and increase the system's overall robustness and ease-of use. Flushing circuits will be added so that measured pore-water pressures will be less affected by diffused air in the system and permeation rates may be more accurately controlled. The entire system will be computer automated and tailored for compatibility with conventional triaxial permeameter systems. Finally, the system performance will be evaluated for a wide range of soil types and the experimental results will be compared with commonly used analytical and empirical models to check their mutual validity. New testing methods are needed to more accurately analyze the increasingly widespread geoenvironmental problems involving unsaturated fluid flow. This research will establish the constant-flow method as a reliable, practical, and economical testing alternative. NIOSH IC 9453, pp. 111-132.

PI：William Likos研究所：科罗拉多矿物学院标题：“开发恒流法同时测量土壤-水特征曲线和非饱和土壤的水力传导函数”分析涉及流体在非饱和土壤中流动的岩土工程和岩土环境工程问题需要两个基本的材料参数：1)土壤-水特征曲线，2)水力传导函数。这些函数共同描述了非饱和土壤中基质吸力、水力传导性和含水率之间的关系。这些函数既可以直接测量，也可以间接模拟。目前，对于这两个重要参数的直接测量，缺乏实用、经济、可靠的实验技术。已经开发了几种技术来独立测量土壤-水特征曲线或渗透系数函数；然而，很少有技术可用于同时测量这两个函数，特别是对于应力控制条件下的单个未受干扰的试件。现有的大多数技术往往不适用于一般用途，因为它们在复杂性和/或成本方面是有限的。因此，工程师在实践中更多地依赖于使用基于常规测量的材料特性(如颗粒尺寸)的分析或经验模型来间接估计特性曲线和电导率函数。然而，在大多数情况下，直接测量是更可取的。本研究试图发展恒流法(CFM)，用于直接、稳态和同时测量非饱和土壤的土-水特征曲线和水力传导函数。大部分工作将以修改原型CFM渗透仪系统的形式进行，该系统是由科罗拉多矿业学院的哈罗德·奥尔森博士与项目合作伙伴S在20世纪90年代中期开发的。早期的结果表明，与更传统的测量技术相比，有几个明显的优势。最值得注意的是，对于单个样品可以获得这两种功能，而不需要对分离的子样品进行单独的测试程序。水力传导度(HC)的测量可以更快地获得，而且水力坡度要小得多。由于试验是在三轴槽中进行的，因此可以将Hc和基质吸力评估为水分含量和施加的有效应力的函数。不幸的是，在原型CFM系统中也有几个明显的限制。具体地说，HC测量仅限于相对细粒的土壤(k 10-8 cm/s)，仅在试件的一端施加孔压，没有安装扩散空气冲洗回路，无法测量试件体积变化，以及由于过于复杂的设计而遇到的渗漏问题。本工作的主要目标是通过解决和消除这些限制来扩大CFM方法在非饱和土壤测试中的能力和实用性。对原型系统的关键修改将允许测量粗粒和细粒土壤的HC，考虑到样品体积的变化，减少测试时间，并增加系统的整体健壮性和易用性。将增加冲洗回路，以使测量的孔隙水压力受到系统中扩散空气的影响较小，并可更准确地控制渗透率。整个系统将是计算机自动化的，并为兼容传统的三轴渗透仪系统而量身定做。最后，将对各种土壤类型的系统性能进行评估，并将实验结果与常用的分析和经验模型进行比较，以验证它们的相互有效性。需要新的测试方法来更准确地分析日益普遍的涉及非饱和流体流动的地质环境问题。本研究将使恒流法成为一种可靠、实用、经济的检测方法。NIOSH IC 9453，第111-132页。