Physically-Based Computational Modeling of Saturated Soil

点击翻译按钮获取中文摘要

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. ***