Structure, Properties and Modeling of Transported Residual Soil

土壤特性的研究历来集中在沉积粘土和干净的沙子，其中材料的微观结构和工程特性的沉积过程和随后的应力历史定义的属性。 与此相反，残积土的结构和性质是由原位风化过程，包括化学溶解和再沉淀控制。 现有的残积土分类和预测其行为的方法是远远不够的，可以直接联系到施工中的问题。 PI最近参与了圣胡安德波多黎各的一个项目，在通过旧冲积层的沉积物的隧道施工期间，意外地发生了大的地面沉降。 进一步的研究已经确定，这种材料可以被归类为运输残留土壤（即，沉积后风化），这类土壤在文献中几乎没有记载，但显然相当普遍。 PI已经获得了大量的土壤块样品，这为研究材料的结构、工程特性和空间变异性提供了极好的机会。 到目前为止，这些初步调查已经确定了铁氧化物作为胶结剂，并发现由于一维压缩试验中结构的破坏，体积导水率显著降低。 该项目将对材料的微观结构进行全面的实验研究，并调查这种结构的破坏如何与剪切强度、变形和流动特性的变化联系起来。 这项工作将受益于先前的研究和高质量块样品的可用性。 从实验程序的数据将被用来制定一个本构模型的基础上，微观结构的概念解释。 然后，模型验证将集中在与破坏相关的材料响应的预测。 该项目将提供一个有价值的和独特的数据库的性质运输，残留土壤比较的行为完整（原位），破坏和内在的属性。 通过了解物质结构，该项目还将有助于残积土分类的标准化。 未来应用一个经过充分验证的本构模型将导致更可靠的预测，在岩土工程分析的项目，在老冲积层和其他类似的存款。

Studies of soil behavior have historically focused on properties of sedimented clays and clean sands in which the material micro-structure and engineering properties are defined by the deposition process and subsequent stress history. In contrast, the structure and properties of residual soils are controlled by in situ weathering processes that involve chemical dissolution and reprecipitation. Existing methods of classifying residual soils and predicting their behavior are far from adequate and can be linked directly to problems in construction. The PI's have recently been involved in a project in San Juan de Puerto Rico, where unexpectedly large ground settlements have occurred during tunneling through deposits of old alluvium. Further research has established that this material can be classified as a transported residual soil (i.e., weathered after deposition), a class of soil barely documented in the literature, but of apparently quite widespread occurrence. Extensive block samples of the soil already obtained by the PI's provide an excellent opportunity to investigate the structure, engineering properties and spatial variability of the material. To date, these preliminary investigations have identified iron oxides as the cementing agent, and have found an extraordinary reduction in bulk hydraulic conductivity due to breakdown in the structure in 1-D compression tests. This project will undertake a comprehensive experimental study of the material micro-structure and investigate how the breakdown in this structure can be linked to changes in the shear strength, deformation and flow properties. The work will benefit from the prior studies and availability of high quality block samples. Data from the experimental program will be used to formulate a constitutive model, based on a conceptual interpretation of the micro-structure. Model validation will then focus on predictions of material response associated with destructuring. This project will provide a valuable and unique database of properties for a transported, residual soil comparing the behavior of intact (in situ), destructured and intrinsic properties. By understanding the material structure, the project will also contribute towards standardizing the classification of residual soils. Future application of a well validated constitutive model will lead to more reliable predictions in geotechnical analyses of projects in the old alluvium and other similar deposits.