Study On Engineering Behavior Of Expansive Soil Subgrade In Western Anhui Under Environmental Heat And Moisture Variation

The expansive soil is one kind of high plastic clay being very sensitive to environmental heat and moisture variation, has the characteristic of expand,strength quickly induced,losing water to shrinkage along with the water content change. The stability of expansive soil subgrade has become an unneglectable important research subject in current highway engineering geology. Therefore, combining the real engineering, studying the characteristics of expansive soils and engineering behavior and its treatment technology of expansive soil subgrades under the environmental heat and moisture variation has important academic meanings and engineering values.Combining Zhouji-Lu'an highway construction project, the identification and classification method, engineering properties, capillary water's ascending height and treatment measure, seepage and stability of expansive soils have been studied synthetically by combining laboratory testing, model testing, theory analysis and numerical modeling, and then the corresponding analysis methods and engineering countermeasures for expansive soils have been put forward. It will provide scientific basis for construction in expansive soil region, at the same time, it will push forward the development of unsaturated soil mechanics and expansive soil mechanics further.The main work in the thesis is as following:The indices that can reflect and characterize swell-shrink mechanism and property were analyzed. The analysis indicates that 5 indices such as liquid limit, plastic limit, the content of colloidal particle, free swell ratio, standard absorption moisture can reflect and characterize swell-shrink mechanism and property, hereby these 5 indices have been suggested as identification and classification indices of expansive soils, and a new approach for identification and classification of expansive soils in western Anhui has been established and the classfication standard has been put forward based on plenty of experiments.Experiments on the physical and mechanical properties of expansive soil in western Anhui have been investigated systematically, and the variation laws and its influencing factors for compacting properties, swelling-shrinkage behavior, intensity and deformation behavior of compacted expansive soils have been summarized. Based on the former research, the applicability of expansive soil in western Anhui used as subgrade filling has been discussed.The improved test of expansive soil in western Anhui with lime and fly ash have been developed, the variation laws and its influencing factors for compacting properties, swelling-shrinkage behavior, intensity and deformation behavior of compacted stabilized expansive soils have been analyzed. Based on the former research, the stabilized scheme and subgrade filling control standard of expansive soil in western Anhui have been discussed.The capillary water effect laws of expansive soil subgrade with different cushion have been investigated by numerical modeling, and one model experiment equipment and the test method was developed to tracing the capillary water upword process for expansive soil subgrade.The effect of cushion material and its disposal thickness to capillary water's ascending height has been analyzed. Combining the result of numerical modeling and model experiment, the bedding disposal measure controlling capillary water effect has been put forward.Aimming at stability of expansive soils under the environmental heat and moisture variation, coupled model for temperature-seepage-stress in expansive soils has been established. Based on the quality conservation law, line momentum balanced principle and law of energy conservation, the control equation group of coupled temperature- seepage- stress in unsaturated soils has been derived, and it is dispersed for finite element with Galerkin method. Through typical coupled example, the correctness of the coupled model and numerical solution has been verified. It will offer theoretical foundation for studying response process of expansive soil subgrade under the environmental heat and moisture variation.Based on above coupled model for temperature-seepage-stress in unsaturated soils, taking the actual evaporation and rainfall in Western Anhui as boundary condition, the effect laws of weather condition variation such as evaporation and rainfall to engineering behavior of subgrade and the deformation law of expansive soil subgrade under the environmental heat and moisture variation have been numerical analyzed. Based on the former research, the engineering disposal measure keeping subgrade long-term stability has been suggested.