SGER: The Elastic Moduli of Soils With Dispersed Oversize Particles

SGER：分散超大颗粒土壤的弹性模量

• 批准号: 0124714
• 负责人: Luis Vallejo
• 金额: $ 5.36万
• 依托单位: University of Pittsburgh
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2003-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0124714&HistoricalAwards=false
• 关键词: SGER; Elastic; Moduli; Soils; Dispersed

To calculate the elastic deformation experienced by soils subjected to static or dynamic loads, knowledge of the elastic moduli is required. Although the response of soils to these kinds of loads may not be strictly represented as linear elastic, solutions based on linear elastic behavior are commonly used for the estimation of stresses or strains in the field. The elastic moduli are normally evaluated in the laboratory using conventional triaxial compressive tests on cylindrical samples. For meaningful test results, it is necessary to maintain a ratio of sample diameter to the maximum particle size of approximately 6:1 or greater. For the conventional triaxial specimen diameter of 2.8 in., the maximum grain size that can be tested is 0.5 in. Thus, when soils are tested in the conventional triaxial apparatus, it is common practice to remove "oversize" particles with an average diameter greater than 0.5 in. Samples larger than 2.8 in. can be used in triaxial testing; however this requires the use of large cells and large loading systems, making the tests too expensive and time consuming to be used routinely. The removal of material larger than 0.5 in. from the samples tested in the conventional triaxial apparatus will provide unreliable elastic moduli values for the calculation of stresses and deformations associated with civil engineering projects built in soils with large rock particles (i.e. glacial tills, residual and colluvial soils). This proposal presents a theoretical method developed by Hashin that calculates the elastic moduli of a composite made of an elastic material containing dispersed large rigid particles. The Hashin method requires only knowledge of the elastic moduli of the matrix that surrounds the particles coupled with the concentration by volume of the rigid large particles in the composite in order to calculate the elastic moduli of the mixture. The objective of this one year exploratory investigation is to assess the validity of the Hashin method by conducting ultrasonic velocity tests on dry mixtures of soils (clay, silt, and sand) and dispersed oversize particles (gravel, glass beads, sands). Also, stress-strain curves reported in the geotechnical literature obtained from conventional static triaxial compression tests on laboratory prepared soils-large particles mixtures will be used to obtain the static elastic moduli. Using the ultrasonic velocity measurements, the laboratory dynamic elastic moduli will be obtained. Using the results from triaxial compression tests, the static elastic moduli will be obtained. The laboratory elastic moduli will be then compared with those predicted by Hashin's theoretical method in order to assess its reliability. The results of the exploratory research will be used as a basis to further explore the validity of Hashin's method as it applies to soil-oversize particle mixtures having a soil matrix with varying degrees of saturation and heterogeneity.

为了计算土壤在静载荷或动载荷作用下的弹性变形，需要了解弹性模量。虽然土壤对这些荷载的响应可能不严格地表示为线弹性，但基于线弹性行为的解决方案通常用于估计现场的应力或应变。弹性模量通常在实验室中使用圆柱形样品的常规三轴压缩试验来评估。对于有意义的测试结果，有必要保持样品直径与最大粒度的比率约为6：1或更大。 对于直径为2.8英寸的常规三轴试样，可以测试的最大粒度为0.5英寸。因此，当在常规三轴仪中测试土壤时，通常的做法是去除平均直径大于0.5英寸的“过大”颗粒。大于2.8 in.的样品可用于三轴测试;然而，这需要使用大的单元和大的加载系统，使得测试过于昂贵和耗时而不能常规使用。 去除大于0.5英寸的材料。在常规三轴仪中测试的样品中，将提供不可靠的弹性模量值，用于计算与在具有大岩石颗粒的土壤（即冰碛土、残积土和崩积土）中建造的土木工程项目相关的应力和变形。该提案提出了一种由Hashin开发的理论方法，该方法计算由含有分散的大刚性颗粒的弹性材料制成的复合材料的弹性模量。为了计算混合物的弹性模量，Hashin方法仅需要围绕颗粒的基质的弹性模量的知识以及复合材料中刚性大颗粒的体积浓度。 这项为期一年的探索性调查的目的是通过对土壤（粘土、淤泥和沙子）和分散的超大颗粒（砾石、玻璃珠、沙子）的干混合物进行超声波速度测试，评估Hashin方法的有效性。此外，应力-应变曲线报告的岩土文献中获得的常规静态三轴压缩试验的实验室制备的土壤大颗粒混合物将被用来获得静态弹性模量。 利用超声波速度测量，将获得实验室动态弹性模量。利用三轴压缩试验的结果，将获得静态弹性模量。然后将实验室弹性模量与Hashin理论方法预测的弹性模量进行比较，以评估其可靠性。 探索性研究的结果将被用作基础，以进一步探讨Hashin的方法的有效性，因为它适用于土壤超大颗粒混合物具有不同程度的饱和度和异质性的土壤基质。