超固结或大埋深地基粗粒土K0演化规律与变形特性试验研究

Accurately predicting the deformation of deep soil foundation is very important to safety design and running of structures. The prediction accuracy, however, is far from satisfaction, especially for cohesionless coarse-grained soils, and even it is difficult to accurately obtain the basic parameter of density. Based on a large number of tests, this project intends to reveal the deformation features of over consolidated or deeply buried coarse-grained soil of ground, and finds appropriate laboratory test approach for determining the mechanical parameters in situ state, and to provide the basis for accurately determining the deformation parameters of the coarse-grained soil of ground. Therefore, the proposed research focuses on the behavior of the coarse-grained soil in four aspects: 1) use a new large-scale K0 apparatus to perform the test for coefficient of lateral pressure at rest K0, and to investigate the rule of the stress variation with time under high pressure; 2) study the K0 variation with time, using the long-term K0 consolidation compression tests, to reveal the relation of lateral pressure against time; 3) study the pattern of K0 with over-consolidation ratio(OCR) for coarse-grained soil, investigate the relation of lateral pressure with OCR and time by using K0 consolidation tests on different OCRs; 4) carry put the triaxial shear test with isotropic consolidation and K0 consolidation, respectively, by large-scale triaxial apparatus, to study the effect of the type and time of consolidation on the strength and deformation behavior of soil. The reliability and accuracy of soil deformation parameters determined using conventional CD test is assessed, and more reasonable test methods would be presented. The achievements of this project will provide basis for accurate calculation of the deformation of over-consolidation or deeply buried coarse-grained soils.

深厚地基变形的准确预测对工程的安全设计与运行十分重要，然而预测精度难以令人满意，尤其对地基无粘性粗粒土，甚至连密度这个最基本的参数都难以准确获得。本项目拟通过一系列试验研究，揭示超固结或大埋深地基粗粒土变形特性，寻求合适的室内试验方法测定其原位状态下力学参数，为准确测定地基粗粒土变形参数提供依据。为此，拟对粗粒土进行四方面研究：1）利用新型大型K0仪进行高压下静止侧压力系数K0研究，研究高压下K0随应力变化规律；2）进行K0固结长期压缩试验，研究K0的时间演化规律，揭示其侧向应力随时间变化关系；3）进行不同超固结比下K0固结试验，研究K0、侧压力随应力、时间变化规律；4）利用大型三轴仪进行等压固结和K0固结条件下的剪切试验，研究固结类型及时间对强度及变形性质的影响，论证现行常用CD试验确定地基土变形参数的可靠性，建议合理试验方法。为超固结或大埋深粗粒土地基变形准确计算提供基础。

深厚地基变形的准确预测对工程的安全设计与运行十分重要，然而预测精度难以令人满意，尤其对地基无粘性粗粒土，甚至连密度这个最基本的参数都难以准确获得。本项目拟通过一系列试验研究，揭示超固结或大埋深地基粗粒土变形特性，寻求合适的室内试验方法测定其原位状态下力学参数，为准确测定地基粗粒土变形参数提供依据。为此，拟对粗粒土进行四方面研究：1）利用新型大型K0仪进行高压下静止侧压力系数K0研究，研究高压下K0随应力变化规律；2）进行K0固结长期压缩试验，研究K0的时间演化规律，揭示其侧向应力随时间变化关系；3）进行不同超固结比下K0固结试验，研究K0、侧压力随应力、时间变化规律；4）利用大型三轴仪进行等压固结和K0固结条件下的剪切试验，研究固结类型及时间对强度及变形性质的影响，论证现行常用CD试验确定地基土变形参数的可靠性，建议合理试验方法。.项目获得的主要研究成果有：（1）对粗颗粒土、粘土、砂土进行了大量的静止侧压力系数试验，揭示了这些土随应力状态、土的种类的变化规律，提出了相应计算公式，填补了粗颗粒土相关研究的空白；并且研究了粗粒土的K0系数缩尺效应，提出了根据室内缩尺替代料试验成果估算现场原级配料的K0系数的方法；（2）通过K0固结长期压缩试验，表明K0随时间变化很小，工程应用情况下基本可以认为是常数；（3）揭示超固结比对K0的影响规律，并提出相应的计算公式；（4）通过试验揭示了等压固结和K0固结条件下的剪切试验的差异，并进行了粗颗粒土天然沉积及人工压实的模拟试验，研究了人工压实及天然沉积条件下卵砾石料的各向异性性质，揭示人工击实粗粒土及天然沉积土的各向异性差异，为室内制备样的代表性提供有力的依据。成果为超固结或大埋深粗粒土地基变形准确计算提供基础。