Interpretation of in Situ Tests in Unsaturated Soils

在美国的岩土工程实践中，用锥形土压力计和预钻孔压力计进行土的原位测试变得越来越普遍。 尤其是静力锥贯入试验（CPT）在咨询工程师中得到了越来越广泛的使用，并且作为会议和会议上感兴趣的主题变得越来越普遍。 压力计（PMT）测试通常用于刚性土壤沉积物中的基础设计，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，有时会延伸到相当深的地方。虽然人们普遍认为非饱和土的特性不同于通常假设的饱和不排水或排水土特性，但没有解释CPT和PMT结果的方法来解释这些差异。 大量的研究已经致力于CPT和PMT，然而，目前还没有可靠的综合方法来解释原位测试结果，从非饱和土。 建议的研究将集中在开发这样一种方法上。20将通过一项研究计划对CPT和PMT进行调查，该研究计划包括实验室土壤测试、校准室测试和分析/数值建模。这项研究计划是长期研究计划的第一步。拟议的研究包括三个主要组成部分：1）设计和开发的校准室和非饱和粉土的测试程序; 2）在室内的非饱和粉土中进行的CPT和PMT;和3）开发一种基于空腔膨胀的非饱和土壤中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;顶盖和基座细节;孔隙空气和孔隙水压力的控制和测量;压力控制系统细节;土壤床制备方法;土壤床仪器; CPT和PMT测试仪器和程序;以及其他。拟进行的研究将使用粉质土，因为与粘土相比，粉质土更容易处理土床准备，并且因为试验粉土的基质吸力值可以用张力计测量。拟议的研究将受益于这样一个事实，即合作PI已经成功地开发了一种技术，用于快速测量基质吸力与小型压力传感器配备了高空气入口多孔石头。在离心机动态加载过程中使用这种技术测量基质吸力的结果表明，这些设备的响应时间是极好的。在室内准备土壤试验床的方法的开发将涉及土壤取样的试错过程，以分析均匀性和可重复性。此外，将使用配备的三轴系统对土床样本进行测试，以确定非饱和土壤特性。 本研究的第二和第三部分包括一系列的CPT和PMT测试在不同的基质吸力下的室内，和解释的数据方面的土壤性质和建模研究的结果。将在非饱和土中进行膨胀圆柱和膨胀球体的有限元建模，以模拟PMT和CPT。该建模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 CAREER研究开发的非饱和土弹塑性本构模型。将使用非饱和三轴试验和PMT校准室试验结果校准该分析结果，并将其用于对相关变量进行参数研究。将开发一种基于分析型腔膨胀的解释方法，用于解释CPT和PMT结果。这将使工程师能够合理地预测土壤在水分条件下的性质，而不是在现场测试时存在的情况。20.这项研究的主要目的是获得关于基质吸力对现场试验结果的影响的重要知识。在实现这一目标的一组有价值的实验数据将建立在土力学领域的信息是稀缺的。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