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

这项拨款提供资金，以调查是否存在一个独特的小应变剪切模量和有效应力之间的关系，在三轴压缩破坏的粘性土。这一假设是根据初步试验，包括各向同性固结排水三轴压缩试验的人工胶结粉质砂剪切波速度测量整个剪切。这些测试有两个重要的发现：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.）存在小应变剪切模量在剪切过程中增加到最大值然后减小的明显趋势，尽管偏应力持续增加直到破坏。为了检验这一假设，将在膨胀状态下对三种不同的土壤进行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。剪切波速度测量将在每次试验的固结和剪切阶段进行。 如果这些发现是一般的排水性或结构性土壤的代表，那么有几个重要的工程实践的影响。这一概念的一个重要应用是直接从土壤中的原位剪切波速度测量中估计有效应力强度参数，这些土壤传统上在实验室中取样和测试是有问题的，例如致密的沙子和淤泥或敏感粘土。拟议关系的建立可能会改变岩土工程现场调查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度测量，例如通过跨孔或地震锥贯入试验，可以用作水泥、结构或敏感土壤在分阶段施工过程中发生破坏的早期预警系统，以及逐渐破坏的自然边坡。

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.