Research On Rheological Consolidation Of Soft Clavev Soils In Dual Scale

Research on macro scale and micro scale are two main streams of the studies on soil mechanics. It is known that soil behavior on macro scale ultimately depend on the characteristics of the soil particle and micro structure. Therefore, micro scale tests and analysis have scientific merit in terms of a fundamental assessment of its mechanism and associated parameters as well as practical implications in terms of explaining soil behavior. Present researches merely involve micro scale testing and analyzing in studies of rheological consolidation, but the mineral composition and micro structure have significant influence on consolidation behavior. Furthermore, rheological consolidation theory which takes soil stress history into account can be seldom found in literature. Bearing all these in mind, the author carried out theoretical and experimental research both on micro and macro scale on rheological consolidation of the soft soils, in order to advance the state-of-the-art with respect to our understanding of the mechanisms and significance of such a classic topic in soil mechanics. Main works are as below:(1) GDS one dimensional advanced consolidation testing system is used in soil laboratory tests to study the non-linearity in compression and recompression of Ningbo clay. Curve fit of the test data provides soil parameters of the non-linear compression models, which laid foundation for the non-linear rheological consolidation theory. Micro scale tests include X-ray EDS, XRD, SEM and MIP tests. X-ray EDS unveils the basic elements and their content in Hangzhou clay, XRD test demonstrates the main minerals in soil, SEM and MIP tests show micro morphological characteristics and pore size distributions of clayey soils after which are consolidated under different stresses.(2) A micro structural catastrophic model for soft soils is presented adopting phenomenological methods, which can describe the rheological consolidation behavior of soft clays. The model is verified by a series of rheological consolidation experiments with different loading rates. Creep deformation, which is loading rate dependent, can be clearly observed in these tests. Model parameters are gained by curve fit from test data. With only two free parameters, good fits of the data are achieved. The characteristics of the parameter demonstrate the feature of the micro-mechanical behavior of the clay.(3) The Gibson-Lo rheological model is used to simulate the coupled processes of drainage and creep of soft soils that takes stress history into account. A hybrid combination of analytical and numerical methods is adopted to solve the governing equations of consolidation with the nonlinear rheological model. The methodology is applied to a saturated soft soil subjected to surface loading. The soil profile is separated into normally consolidated and overconsolidated layers by a boundary that is allowed to move. Comparisons of the model predictions and its simulations are used to evaluate the effects of stress history, model parameters, and loading pattern on consolidation behavior. In non-linear analysis, variations in compressibility and permeability are captured using bi-linear e-logp and e-logkv models with the break in behavior controlled by the yield stress. The relative magnitude of the applied stress to the yield stress of clays is found to influence the rate of consolidation as well as the ultimate settlement. In addition, the ratios of the model parameters Cc/Ck, Ce/Cc and Cke/Ck are shown to have different effects on the consolidation behavior of clays.(4) The final section is on the increased yield stress of clays due to time effects termed the quasi-preconsolidation pressure. A nonlinear rheological model for clays incorporated into the governing equation is used to numerically simulate the consolidation process of clay in laboratory tests to identify the basic mechanical parameters that contribute to the development of the quasi-preconsolidation phenomenon. A change in modulus in the recompression region due to ageing is shown to be the dominant cause of the development of the quasi-pc phenomenon. While the soil modulus variation controls the EOP curve of clays, observed time effects such as the "vanishing pc" phenomenon are controlled primarily by changes in soil viscosity. This has no bearing on the development of the quasi-pc phenomenon.