Modeling Of Modified Subgrade For Couped Thermo-Hydro-Mechanical-Chemical Processes And Numerical Simulation For Deformation Of Subgrade

With the research object of expansive soil in Nanning, Guangxi, the mechanism of expansiveness and shrinking of expansive soils is analyzed based on the combination of macroscopic and microcosmic analysis and the combination of theory and examination. The two important factor (drying-and-wetting cycle and eluviations) influencing on the expansive soils roadbed modified with lime were studied based on the laboratory examination, the destroying mechanism was analyzed based on the microcosms. Based on the equations of coupled thermo-fluid-mechanical-chemistry, a model of the modified expansive soils subgrade responding to the change of atmosphere is established. The process of subgrade responding to the change of atmosphere is simulated, and the effects of drying-and-wetting cycle and eluviations on the strength and deformation of the long-term performance of the modified subgrade with lime. The main outcomes are as follows:1. The mechanism of expansiveness and shrinking of expansive soils is analyzed more deeply based on the combination of macroscopic and microcosmic analysis: the expansiveness and shrinking foundation of expansive soils is montmorillonite minerals containing d(001) layer with the ability of drinking and draining.2. Based on the results of the laboratory examination of drying-and–wetting cycle of the modified expansive soils with lime, it is shown that with the increase of the times of drying-and-wetting cycle the strength parameters C is obviously decreased and the change ofΦis very little. Because the subgrade strength is decreased under the influence of drying-and-wetting cycle, the influence of drying-and-wetting cycle should be considered when the long-term performance of the modified subgrade is analyzed. 3. The long-term performance of the modified subgrade is influenced by many factors, the eluviations is often not considered. Based on the results of the laboratory examination of eluviations of the modified expansive soils with lime, it is shown that the strength of the modified soils is decreased with the decrease of the content of Ca²⁺. The influence of the decrease of the content of Ca²⁺ on the strength is disadvantageous to long-term performance of subgrade.4. Based on the equations of coupled thermo-fluid-mechanical-chemistry, a model of the modified expansive soils subgrade responding to the change of atmosphere is established. The process of subgrade responding to the change of atmosphere is simulated, the change rules of the fluid, temperature and the content of Ca²⁺ are calculated. Based on the results of calculation of the effects of drying-and-wetting cycle and eluviations on the strength and deformation under the loading of cars and weight of subgrade. It is shown that under the effect of drying-and-wetting cycle,eluviations and loading, the strength of subgrade is decreased and the deformation is increased remarkablely. The engineering measures maintaining the long-term performance of the modified subgrade with lime are advised based on the calculation results.