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

该基金用于研究在三轴压缩条件下膨胀土的小应变剪切模量和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进行的各向同性固结排水三轴压缩试验的初步试验，并在剪切过程中测量剪切波速。这些试验有两个重要的发现：1)对于给定的土壤，小应变剪切模量与破坏时的主有效应力之比是恒定的，与胶结程度、密度和固结应力无关；2)在剪切过程中，小应变剪切模量有明显的先增大后减小的趋势，尽管偏离应力持续增大直至破坏。为了验证这一假设，将在三种不同的膨胀状态下的土壤上进行ko固结排水三轴压缩试验：粗砂、角砂、非塑性粉砂和高塑性粘土。剪切波速测量将在每次试验的整个固结和剪切阶段进行。如果这些发现是典型的膨胀土或结构性土，那么对工程实践有几个重要的意义。这一概念的一个重要应用将是直接从土壤的原位剪切波速测量中估计有效应力强度参数，这些参数传统上在实验室中取样和测试是有问题的，例如致密砂和粉砂或敏感粘土。建立拟议的关系可能会改变岩土工程现场调查和实验室测试程序的设计方式。另一个应用将是原位横波速度测量，例如从交叉孔或地震锥贯入试验中，可以用作在堤防和自然边坡逐步破坏的阶段施工期间发生破坏的水泥、结构或敏感土壤的早期预警系统。

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.