Multiscale Modeling of Thixotropy in Soft Clays

Thixotropy is a material property that describes how a substance can 'soften' upon continues deformation and heal back to the 'thicker' state over time when left to rest. It is also a fundamental soil behavior mechanism that governs multiple time-dependent engineering properties of soft clays (e.g., the evolution of stiffness, strength, and sensitivity over time).While significant understanding of thixotropy of colloid systems has been achieved since the initiation of the field of thixotropy in the early 1920s, current knowledge on soil thixotropy is still based primarily on some pioneering work performed in and prior to the 1960s and, since then, new developments have been scarce and fragmental. Such a paucity of new findings and the disparity in thixotropy research and advancement between colloid science and soil mechanics provide an impetus to this research. Therefore, this project that integrates multiscale computational and experimental efforts is to study soft clay thixotropy. The work done in this study aims to examine and simulate the clay particle-scale development of thixotropy under various environmental conditions (time, water chemistry, and temperature) and at different size scales. This innovative bottom-up multiscale modeling approach serves to understand the physics underlying macroscopic soft clay thixotropic behavior. The overall goal of the project is to create the enabling knowledge on the macroscale mechanical and microscale structural mechanisms of soft clay thixotropy and hence to append some new time-dependent soil behavior to the geotechnical knowledge base. It is to develop an understanding of the micro- to macro-linkage of soft clay thixotropy through the development of a versatile molecular dynamics (MD) simulation tool to accurately duplicate the time-dependent interactions between clay particles and to provide a framework for the study of the three-dimensional mechanical behavior of soft clays. The value of this project stems from three aspects: (1) the geotechnical knowledge base on soil thixotropy will be expanded with new understanding, particularly the effects of physico-chemical factors such as temperature and porewater chemistry; (2) both the macroscale mechanical and microscale structural mechanisms of thixotropic hardening of soft clays will be uncovered via multiscale computational research; and (3) the linkage between quantitative time-dependent clay fabric evolution and macroscale thixotropic processes will be developed. Because soil thixotropy plays an important role in many engineering problems, the project also can generate significant practical impacts to geotechnical engineering, particularly the design and construction of engineering systems involving soft clays. Examples include evaluation of pile and suction caisson setup, design of wind farm foundations, and disposal of dredged materials, among others. Moreover, the multiscale investigation methodology developed through this project can be generalized to other more complex soil research topics and can also serve as a generic approach for other basic research queries.Ph.D., Civil engineering -- Drexel University, 201