Collaborative Research: International Development of Non-Destructive Tools to Quantify Sample Disturbance and Its Correlation to Measured Behavior

CMS- 0218314PI: Thomas sheahan机构：东北大学标题：“合作研究；摘要：虽然在使用现场测试和地球物理方法确定设计的土壤应力-应变-强度参数方面取得了重要进展，但在可预见的未来，实践状态往往依赖于物理土壤样品采集进行实验室测试。为实验室测试收集的样品往往受到高度干扰，但岩土工程专业没有足够的非破坏性工具来评估这种干扰或将其与现场或实验室测试中测量的行为联系起来。现有的评估样品扰动的方法，如实验室重固化时的体积应变，并不是先验的方法，也就是说，直到实验室样品被修剪并设置在测试设备中，人们才知道样品的质量。与此同时，我们面临着越来越苛刻的岩土工程设计和分析问题，这些问题需要基于现场试验和实验室物理样品试验对土壤行为进行更准确的估计。基础设施设计的要求以及诸如海底滑坡分析等更大规模的问题要求岩土工程师不仅要给出保守的答案，而且要给出正确的答案，即尽可能接近“真实”的原位力学特性。这个为期三年的项目涉及国际合作，旨在改善我们在软土地基取样技术方面的现有实践状况，开发更好的评估样品扰动的技术，并改进现场测量的机械性能、样品扰动程度和实验室测量的样品力学性能之间的关系。来自马萨诸塞大学阿默斯特分校和东北大学的主要研究人员正在建立超过15年的采样，实验室测试和设备创新的个人和联合经验，以帮助解决软土地基工程领域长期存在的问题。此外，该项目还扩展了与挪威岩土研究所（NGI）的现有合作伙伴关系，共同开发可现场部署的非破坏性样品干扰评估技术。该项目包括：1)开发用于常规美国钻机的井下区块取样设备；2)对北美4个地点不同结构程度的多种土壤类型进行取样，采用常规的管样和块样两种取样方法；3)在四个地点进行地震压电锥（CPTU）试验，获得CPTU基线测量值和现场剪切模量（Gmax）；4)开发了现场吸力探头和弯曲元件装置，分别对块状和常规管状试样进行有效应力和Gmax评估；5)在实验室测试装置中实施弯曲单元，以测量试样建立后和小应变水平下的Gmax；6)利用改造后的设备进行室内测试程序，综合测量四种土的应力-应变-强度特性，包括中、小应变；7)在样品扰动程度和土壤结构程度的背景下，建立现场和实验室测量行为之间的精确相关性。预计这项工作的结果将对软土取样的技术现状和实践状况产生影响，并将干扰效应与测量行为相关联。可以建立一个综合的框架，将样品扰动与土壤的结构和各向异性等基本特性联系起来。块抽样方法将被证明是美国实践的可行工具，并且正在开发用于定量评估样本干扰的实践标准。样品扰动和测量行为之间的相关性最终将提高实验室结果的准确性，而不是真实的原位行为，从而更可靠的岩土工程设计，而不是过度保守。

CMS- 0218314PI: Thomas SheahanInstitution: Northeastern UniversityTitle: "Collaborative Research: International Development of Non-Destructive Tools to Quantify Sample Disturbance and its Correlation to Measured Behavior"Abstract:While important progress has been made in the use of in situ testing and geophysical methods to determine soil stress-strain-strength parameters for design, the state of practice for the foreseeable future will often rely on physical soil sample collection for laboratory testing. Samples collected for laboratory testing are often highly disturbed, but the geotechnical profession does not have adequate non-destructive tools for evaluating that disturbance or correlating it to the measured behavior either in situ or in laboratory tests. Existing methods of assessing sample disturbance, such as volumetric strain upon laboratory reconsolidation, are not a priori methods, i.e., one does not know a sample's quality until a laboratory specimen has been trimmed and set up in a testing device. At the same time, we face increasingly demanding geotechnical design and analysis problems that require more accurate estimates of soil behavior based on both in situ tests and laboratory tests on physical samples. The demands of infrastructure design as well as larger scale problems such as submarine landslide analyses require geotechnical engineers to produce not just a conservative answer, but the right answer, i.e., the closest to the "true" in situ mechanical properties as possible.This three year project involves an international effort to improve our existing state of practice in soft ground sampling technology, develop better techniques for assessing sample disturbance, and develop improved relationships between field-measured mechanical properties, the degree of sample disturbance, and the laboratory-measured mechanical properties from those samples. The Principal Investigators from the University of Massachusetts Amherst and Northeastern University are building on over 15 years of individual and joint experience in sampling, laboratory testing and equipment innovation to help solve this longstanding problem in the field of soft ground engineering. In addition, the project extends an existing partnership with the Norwegian Geotechnical Institute (NGI) to jointly develop field-deployable non-destructive sample disturbance evaluation techniques. The project involves: 1) developing down-hole block sampling equipment for use with conventional U.S. drill rigs; 2) sampling a variety of soil types with different degrees of structure from 4 locations in North America, using both conventional tube and block sampling methods; 3) performing seismic piezocone (CPTU) tests at the four sites to obtain baseline CPTU measurements and in situ shear modulus (Gmax); 4) developing a field suction probe and bender element device to evaluate sample effective stress and Gmax, respectively, in block and conventional tube samples; 5) implementing bender elements in laboratory test devices to measure Gmax after specimen set-up and at small strain levels; 6) conducting a laboratory testing program with the modified equipment to comprehensively measure the stress-strain-strength behavior of the four soils, including that at small and medium strains; 7) developing accurate correlations between the field- and lab-measured behavior in the context of the degree of sample disturbance and degree of soil structure.It is anticipated that the results from this work will have an impact on the state of the art and state of practice in sampling soft soils and correlating disturbance effects to measured behavior. A comprehensive framework can be established to link sample disturbance with soil behavior fundamentals such as structure and anisotropy. The block sampling method will be demonstrated as a viable tool for U.S. practice, and a standard of practice is being developed for quantitative assessment of sample disturbance. The correlations between sample disturbance and measured behavior will ultimately lead to improved accuracy in laboratory results versus the true in situ behavior, and thus more reliable geotechnical design without excessive conservatism.