Unique Relationship Between Small Strain Shear Modulus and Effective Stresses at Failure for Dilative Soils

这笔资金用于研究在膨胀土的三轴压缩过程中，小应变剪切模数和破坏时的有效应力之间是否存在独特的关系。这一假设是基于对人工胶结粉质砂土的各向同性固结排水三轴压缩试验的初步试验，并在整个剪切过程中进行了剪切波速测量。这些测试有两个重要的发现：1)对于给定的土体，破坏时的小应变剪切模数与主有效应力的比值是恒定的，与胶结程度、密度和固结应力无关；有一个明显的趋势，小应变剪切模数在剪切过程中增加到一个最大值，然后下降，尽管偏应力持续增加，直到破坏。为了验证这一假设，将在三种不同的膨胀状态下进行Ko固结排水三轴压缩试验：粗砂、角砂、非塑性粉土和高塑性粘土。剪切波速测量将在每个试验的固结和剪切阶段进行。如果这些发现在总体上代表了膨胀土或结构性土，那么对工程实践就有几个重要的启示。这一概念的一个重要应用将是直接从土壤中的现场剪切波速测量估计有效应力强度参数，这些土壤传统上在实验室采样和测试时存在问题，例如致密的沙子和粉土或敏感的粘土。拟议关系的建立可能会改变岩土现场勘察和实验室测试计划的设计方式。另一个应用是，现场剪切波速测量，例如跨孔或地震触探试验，可以用来作为分期建造路堤和逐渐失稳的天然斜坡期间水泥土、结构性或敏感土壤中失稳开始的预警系统。

This grant provides funding to investigate whether a unique relationship exists between small strain shear modulus and effective stresses at failure during triaxial compression for dilatant soils. This hypothesis was developed based on preliminary tests involving isotropically consolidated drained triaxial compression tests on an artificially cemented silty sand with shear wave velocity measurements made throughout shearing. There were two important findings from these tests: 1.) the ratio of small strain shear modulus to principal effective stress at failure was constant for the given soil, independent of the degree of cementation, density, and consolidation stress; and 2.) there was a clear trend of the small strain shear modulus increasing during shear to a maximum value and then decreasing despite continued increases in the deviator stress up to failure. To test this hypothesis, Ko-consolidated drained triaxial compression tests will be performed on three different soils in a dilative state: coarse, angular sand, non-plastic silt, and high plasticity clay. Shear wave velocity measurements will be made throughout the consolidation and shear phases of each test. If these findings are representative of dilatant or structured soils in general, then there are several important implications for engineering practice. A significant application of this concept would be the estimation of effective stress strength parameters directly from in situ shear wave velocity measurements in soils that have been traditionally problematic to sample and test in the laboratory, such as dense sands and silts or sensitive clays. Establishment of the proposed relationship would potentially change how geotechnical site investigations and laboratory testing program are designed. Another application would be that in situ shear wave velocity measurements, for example from cross-hole or seismic cone penetration tests, could be used as an early warning system for the onset of failure in cemented, structured, or sensitive soils during staged construction of embankments and natural slopes which fail progressively.