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: 0200974
• 负责人: William Likos
• 金额: $ 4.91万
• 依托单位: Colorado School of Mines
• 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: 2002-09-01 至 2003-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0200974&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.

主要研究者：William Likos机构：科罗拉多矿业学校名称：“开发用于同时测量非饱和土壤的土-水特征曲线和水力传导函数的恒流方法“分析涉及流体通过非饱和土壤流动的岩土工程和地质环境工程问题需要两个基本材料参数：1）土-水特征曲线，和2）水力传导函数。 这些函数共同描述了非饱和土中基质吸力、导水率和含水量之间的关系。 这两个函数既可以直接测量也可以间接建模，但目前还缺乏实用、经济、可靠的实验技术来直接测量这两个重要参数。 已经开发了几种技术，用于独立测量土壤-水特征曲线或水力传导率函数;然而，很少有可用于同时测量这两个功能，特别是在应力控制条件下的单个未受干扰的标本。大多数现有技术对于一般用途往往是不切实际的，因为它们在复杂性和/或成本方面受到限制。 因此，工程师在实践中更经常依赖于使用基于常规测量的材料特性（例如粒度）的分析或经验模型来间接估计特征曲线和电导率函数。本研究尝试发展一种可直接、稳态、同步量测非饱和土之土水特征曲线与水力传导函数之恒流法。 这项工作的大部分将是在一个原型CFM渗透系统的修改形式，在90年代中期开发的项目合作PI哈罗德奥尔森博士在科罗拉多矿业学校。 早期的结果表明，与传统的测量技术相比，它有几个明显的优势。最值得注意的是，这两个功能可以获得一个单一的样本，而不需要单独的测试程序的分裂子样本。 水力传导率（HC）的测量可以得到更快，并与实质上更小的水力梯度。 由于试验是在三轴单元中进行的，HC和基质吸力可以作为含水量和施加有效应力的函数进行评估。 不幸的是，在原型CFM系统中也存在一些明显的局限性。 具体来说，HC测量仅限于相对细粒的土壤（k 10 - 8 cm/sec），孔隙空气压力仅施加在样品的一端，没有引入扩散空气冲洗回路，不能测量样品体积变化，本文的主要目的是扩展CFM方法的能力和实用性通过解决和消除这些限制来进行非饱和土壤测试。 对原型系统的关键修改将允许HC测量粗颗粒和细粒土壤，考虑试样体积变化，减少测试时间，并增加系统的整体鲁棒性和易用性。 将增加冲洗回路，以便测量的孔隙水压力受系统中扩散空气的影响较小，并且可以更准确地控制渗透率。 整个系统将是计算机自动化的，并与传统的三轴渗透系统兼容。 最后，系统的性能将被评估为广泛的土壤类型和实验结果将与常用的分析和经验模型进行比较，以检查它们的相互有效性。 需要新的测试方法来更准确地分析涉及非饱和流体流动的日益普遍的地质环境问题。 这项研究将建立一个可靠的，实用的，和经济的测试替代恒流法。NIOSH IC 9453，pp. 111-132.