Physically-Based Computational Modeling of Saturated Soil

大地震可引起地表土层的横向和垂直运动，这可能导致较大的永久位移。其后果是破坏地下管道和地面设施，如道路、桥梁和建筑物。在沿海地区，饱和土壤可能在地震中液化，对人造设施造成破坏。协助土壤工程师和地球物理学家研究液化和由此导致的土壤破坏的必要科学工具是具有预测能力的基于物理的计算模型。这个研究项目的目的就是开发这样的工具。目标是创建具有预测能力的基于科学的计算工具，以解决液化和土壤破坏现象。解决以下任务：1。通过直接观察在土壤样品中嵌入的铅掺杂颗粒的线和层的变形历史，并将其与整体响应联系起来。带有x射线附件的特殊单元提供了研究样品内部变形运动学的工具。它提供了洞察饱和颗粒介质在液化过程中的变形的能力。它还允许研究剪切带的开始和发展。初步观察表明，即使在液化试样中，在每个循环过程中，随着变形变大，也会产生剪切带。研究了这种剪切带的发展过程，以及它们如何随着变形周期的逆转而变化。对排水和不排水的样品都进行了研究。2. 直接观察和量化剪切带区的微观组织。特殊的单元用于在排水和不排水饱和样品中创建受控剪切带。然后用聚酯树脂浸渍样品，并使其固化。通过这种方式，可以捕获样品内剪切带的微观结构。一旦达到所需的状态，砂体就会在原地凝固。从凝固后的样品上切下薄片进行显微分析。在剪切局部化过程中，最终形成局部化带的区域内的颗粒可能会发生较大的旋转，而靠近最终剪切带的颗粒可能仍然保持局部化前的方向和相对位置。通过研究局部化区域相邻区域的微观结构，并与局部化区域内的变形进行比较，可以完整地记录由均匀变形状态向高度局部化非均匀变形状态转变的过程，并对剪切区域及其邻域进行拍照，进行完整的统计和确定性分析。这些结果用于指导剪切带开始前、剪切带形成期间以及剪切带完全发育后剪切带内变形的理论建模。＊＊＊

9523959 Nemat-Nasser Major earthquakes can cause lateral and vertical motion of the surface soil layers, which may result in large permanent dis placements. A consequence is damaged underground pipelines and surface facilities such as roads, bridges, and buildings. In coastal regions, saturated soils may liquefy during an earthquake, resulting in damage to man-made facilities. The necessary scientific tools for assisting soil engineers and geophysicists concerned with liquefaction and the resulting soil failure are physically-based computational models with predictive capability. The aim of this research program is to develop such tools. The goal is to create science-based computational tools with predictive capability in order to address the liquefaction and soil failure phenomena. The following tasks are addressed: 1. Examine by direct observation the history of the deformation of lines and layers of lead-doped granules embedded in a soil sample, and relate this to the overall response. A special cell with X-ray attachment provides a tool to study the kinematics of deformation inside the sample. It provides the capability to obtain insight into the deformation of a saturated particulate medium during its liquefaction. It also permits the study of the inception and growth of shearbands. Preliminary observations suggest that even in a liquefied sample, shearbands can be induced, as the deformation becomes large, during each cycle. The development of such shearbands is examined as they develop, and how they change as the deformation cycle is reversed. Both drained and undrained samples are investigated. 2. Directly observe and quantify the microstructure in shearband zones. The special cell is used to create controlled shearbanding in both drained and undrained saturated samples. The sample is then impregnated with polyester resin, and solidified. In this manner, the microstructure of the shearbands within the sample can be captured. The sand mass is so lidified in situ, once a desired state is reached. Thin sections are cut from this solidified sample for microscopic analysis. During shear localization, the particles in the region which eventually forms the localized band may undergo large rotations, whereas particles adjacent to the eventual shearing zone may still retain their orientation and relative position that existed prior to the localization. By studying the microstructure of a zone adjacent to the localized region and comparing the deformation with that within the zone, a complete picture of the transition from a homogeneous to a highly localized heterogeneous deformation state can be documented, Pictures are taken of the shear zones and their neighborhoods for complete statistical and deterministic analysis. These results are used to guide the theoretical modeling of the deformation prior to shearband inception, during shearband formation, and within the shearband, once it has fully developed. ***