Interpretation of in Situ Tests in Unsaturated Soils

在美国，使用锥入度计和预钻孔压力计对土壤进行现场测试在岩土工程实践中变得越来越普遍。 尤其是锥入度测试 (CPT) 在咨询工程师中得到了更广泛的使用，并且作为会议和会议上感兴趣的话题变得越来越普遍。 压力计 (PMT) 测试通常用于硬质土壤沉积物的基础设计，并且在美国实践中也变得越来越普遍。 在地下勘探过程中，通常会遇到非饱和土壤区域，有时会延伸到相当深的深度。虽然人们普遍认为非饱和土的行为不同于通常假设的饱和不排水或排水土的行为；没有任何方法可以解释 CPT 和 PMT 结果来解释这些差异。 对 CPT 和 PMT 进行了大量的研究；然而，目前还没有可靠的综合方法来解释非饱和土的现场测试结果。 拟议的研究将集中于开发这种方法。=20 CPT 和 PMT 将通过一项研究计划进行研究，其中包括实验室土壤测试、校准室测试和分析/数值建模。这项研究计划代表了长期研究计划的第一步。拟议的研究包括三个主要部分：1）设计和开发校准室以及非饱和淤泥的测试程序； 2) 在室内不饱和淤泥中进行 CPT 和 PMT； 3）开发基于空腔膨胀的非饱和土中 CPT 和 PMT 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；土床准备方法；土床仪器； CPT和PMT测试设备和程序；和其他人。拟议的研究将利用粉质土壤，因为与粘土相比，它在土床准备方面更容易处理，并且因为测试淤泥的预期基质吸力值可以用张力计测量。拟议的研究将受益于 Co-PI 已成功开发出一种使用配备高空气进入多孔石材的小型压力传感器快速测量基质吸力的技术。在离心机动态加载过程中使用该技术进行的基质吸力测量结果表明，这些设备的响应时间非常出色。在室内准备土壤试验床的方法的开发将涉及土壤取样的反复试验过程，以分析均匀性和可重复性。此外，土床样品将使用配备的三轴系统进行测试，以确定非饱和土的行为。 这项研究的第二和第三部分包括在不同基质吸力下在室内进行的一系列 CPT 和 PMT 测试，以及根据土壤特性和建模研究结果对数据进行解释。对非饱和土中的膨胀圆柱体和膨胀球体进行有限元建模，以模拟 PMT 和 CPT。该建模将使用全耦合有限元分析方法进行，该方法利用通过 Co-PI=EDs CAREER 研究开发的非饱和土弹塑性本构模型。该分析的结果将使用不饱和三轴测试和 PMT 校准室测试结果进行校准，并且还将用于对感兴趣的变量进行参数研究。将开发基于分析空腔膨胀的解释方法来解释 CPT 和 PMT 结果。这将使工程师能够对现场测试时以外的湿度条件下的土壤特性做出合理的预测。=20 这项研究的主要目标是获得有关基质吸力对现场测试结果影响的重要知识。为了实现这一目标，将在信息稀缺的土壤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，并开发准备和测试非饱和土床的方法。=20

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