Structure, Properties and Modeling of Transported Residual Soil

对土壤行为的研究历来集中在沉积粘土和洁净砂的性质上，其中材料的微观结构和工程性质是由沉积过程和随后的应力历史决定的。相比之下，残余土的结构和性质受化学溶解和再沉淀等原位风化过程的控制。现有的残余土分类和预测其行为的方法远远不够，并且可以直接与施工中的问题联系起来。PI最近参与了波多黎各圣胡安的一个项目，在那里，在旧冲积层的沉积物中挖掘隧道时，意外地出现了巨大的地面沉降。进一步的研究表明，这种物质可以被归类为搬运残余土（即沉积后风化），这类土壤在文献中几乎没有记录，但显然相当普遍。PI已经获得了大量的块状土壤样本，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。迄今为止，这些初步研究已经确定氧化铁为固井剂，并且在一维压缩测试中发现，由于结构的破裂，总体水力导电性显著降低。该项目将对材料的微观结构进行全面的实验研究，并研究这种结构的破裂如何与抗剪强度、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的可用性。从实验程序的数据将用于制定本构模型，基于微观结构的概念解释。然后，模型验证将侧重于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特性数据库，用于比较运输残余土的完整（原位），破坏和固有特性的行为。通过对物质结构的了解，该项目也将有助于规范残积土的分类。未来应用一个验证良好的本构模型，将在老冲积层和其他类似矿床的工程岩土分析中产生更可靠的预测。

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.