Interpretation of in Situ Tests in Unsaturated Soils

非饱和土现场试验的解释

• 批准号: 9813137
• 负责人: Gerald Miller
• 金额: $ 20.69万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-09-01 至 2002-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9813137&HistoricalAwards=false
• 关键词: Interpretation; Situ; Tests; Unsaturated; Soils

In situ testing of soil with the cone penetrometer and pre-bored pressuremeter are becoming more commonplace in geotechnical engineering practice in the United States. The cone penetration test (CPT) in particular is seeing more widespread use among consulting engineers, and is becoming increasingly prevalent as a topic of interest at conferences and meetings. Pressuremeter (PMT) testing is often used for foundation design in stiff soil deposits, and also is becoming more prevalent in US practice. During a subsurface exploration, a zone of unsaturated soil is usually encountered, sometimes extending to considerable depth. While it is generally understood that the behavior of unsaturated soils is different from the commonly assumed saturated-undrained or drained soil behavior; there are no methods for interpreting CPT and PMT results that account for these differences. A great deal of research has been devoted to the CPT and PMT; however, there are currently no reliable comprehensive methods for interpreting in situ test results from unsaturated soils. The research proposed will focus on the development of such a method.=20 The CPT and the PMT will be investigated through a research program that includes laboratory soil testing, calibration chamber testing, and analytical/numerical modeling. This research proposal represents the first step in a long-range research plan. The proposed research includes three major components: 1) design and development of a calibration chamber and testing procedure for unsaturated silt; 2) CPTs and PMTs conducted in an unsaturated silt within the chamber; and 3) development of a cavity expansion based method of interpretation for the CPT and PMT in unsaturated soil. The first research component involves several important considerations including: chamber geometry; top cap and pedestal details; control and measurement of pore air and pore water pressure; pressure control system details; soil bed preparation methods; soil bed instrumentation; CPT and PMT testing apparatus and procedures; and others. Research proposed will utilize a silty soil because it is easier, compared to clay, to handle in terms of soil bed preparation, and because matric suction values expected for the test silt can be measured with tensiometers. The proposed research will benefit from the fact that the Co-PI has successfully developed a technique for rapid measurement of matric suction with small pressure transducers equipped with a high-air entry porous stone. Results of matric suction measurements using this technique during dynamic loading in a centrifuge indicate that the response time of these devices is excellent. Development of methods for preparing soil test beds in the chamber will involve a trial and error process with soil sampling for analyzing homogeneity and repeatability. In addition, samples from soil beds will be tested with a triaxial system equipped to define the unsaturated soil behavior. Second and third components of this research include a series of CPT and PMT tests in the chamber under different matric suctions, and interpretation of the data in terms of soil properties and outcome of modeling studies. Finite element modeling of an expanding cylinder and an expanding sphere in an unsaturated soil will be performed to simulate the PMT and CPT. This modeling will be performed using a fully-coupled finite element analysis method that utilizes an elastoplastic constitutive model for unsaturated soil, developed through the Co-PI=EDs CAREER research. The results of this analysis will be calibrated using unsaturated triaxial test and PMT calibration chamber test results, and will also be used to conduct a parametric study of the variables of interest. An analytical cavity expansion based method of interpretation will be developed for interpretation of CPT and PMT results. This will allow engineers to make reasonable predictions of soil properties at moisture conditions other than those that exist when the in situ tests are performed.=20 A primary goal of this research is to gain important knowledge about the influence of matric suction on in situ test results. In accomplishing this goal a valuable set of experimental data will be established in an area of soil mechanics where information is scarce. A unique calibration chamber will be constructed and methods for preparing and testing unsaturated soil beds will be developed.=20

在美国的岩土工程实践中，用圆锥贯入仪和预钻孔压力计现场测试土体变得越来越常见。尤其是锥体渗透测试(CPT)在咨询工程师中得到了越来越广泛的使用，并越来越成为各种会议上感兴趣的话题。压力计(PMT)测试常用于刚性土地基的基础设计，在美国的实践中也变得越来越普遍。在地下勘探中，通常会遇到一层非饱和土层，有时会延伸到相当深的地方。虽然人们普遍认为非饱和土壤的行为不同于通常假设的饱和-不排水或排水土壤的行为；但没有方法来解释这些差异的CPT和PMT结果。人们对静力触探和静力触探进行了大量的研究，但目前还没有一种可靠的综合方法来解释非饱和土的现场试验结果。建议的研究将集中于这种方法的开发。=20将通过包括实验室土壤测试、校准室测试和分析/数值模拟的研究计划来研究CPT和PMT。这项研究计划是长期研究计划的第一步。拟议的研究包括三个主要部分：1)设计和开发非饱和粉土校准室和测试程序；2)在非饱和粉土中进行CPT和PMT；3)发展基于空穴扩张的非饱和土壤中CPT和PMT的解释方法。第一个研究部分涉及几个重要的考虑因素，包括：腔室几何形状；顶盖和底座细节；孔隙空气和孔隙水压力的控制和测量；压力控制系统细节；土床制备方法；土床仪器；CPT和PMT测试设备和程序；以及其他。拟议的研究将使用粉质土壤，因为与粘土相比，粉质土壤在土床准备方面更容易处理，而且试验粉土的基质吸力值可以用张力计测量。这项拟议的研究将受益于这样一个事实，即Co-PI已经成功地开发了一种利用配备高空气入口多孔石的小型压力传感器来快速测量基质吸力的技术。用该技术在离心机上进行动态加载时的矩阵吸力测量结果表明，这些装置的响应时间是很好的。在室内准备土壤试验台的方法的开发将涉及对土壤采样进行反复试验的过程，以分析均质性和重复性。此外，来自土壤床的样品将用配备有确定非饱和土壤特性的三轴系统进行测试。本研究的第二部分和第三部分包括在不同基质吸力作用下室内进行的一系列CPT和PMT测试，并根据土壤特性和模型研究结果对数据进行解释。对非饱和土体中的膨胀圆柱体和膨胀球进行有限元模拟，以模拟PMT和CPT。该模型将使用完全耦合的有限元分析方法进行，该方法利用通过Co-PI=EDS职业研究开发的非饱和土弹塑性本构模型。这项分析的结果将使用非饱和三轴试验和PMT校准室试验结果进行校准，并将用于对感兴趣的变量进行参数研究。将开发一种基于分析腔膨胀的解释方法，用于解释CPT和PMT结果。这将使工程师能够在水分条件下对土壤性质做出合理的预测，而不是在进行现场测试时存在的条件。=20这项研究的主要目标是获得关于基质吸力对现场测试结果的影响的重要知识。为了实现这一目标，将在信息稀缺的土力学领域建立一组有价值的实验数据。将建造一个独特的校准室，并开发制备和测试非饱和土层的方法。