Experimental Research On Structure Characteristics Of Unsaturated Remolded Expansive Soils

This thesis is a part of the project of"Research of structures and strength of unsaturated expansive soils"which is supported by National Natural Science Foundation of China (No.40374047). A number of laboratory tests, including the microstructure, the strength and strain characteristics and the soil-water characteristic curves of Guangxi and Hefei expansive soils, were undertaken and the test results were analyzed based on the principle of unsaturated soil mechanics. The main results are included as follows:1. The properties of Guangxi and Hefei expansive soils were studied and analyzed firstly. Then, the microstructure of remoulded Guangxi expansive soil was studied through the tests of scanning electron microscope and mercury intrusion pore size distribution. The influence of dry density on microstructure was analyzed. Based on fractal theory, the features of distribution of pores are discussed.2. A number of suction-controlled triaxial tests were performed on remoulded Guangxi expansive soil. The influence of initial dry density, net confining stress and suction on subsequent soil behavior was investigated by the change of microstructure, which is revealed by the tests of scanning electron microscope, mercury intrusion and the optical image measurement results of soil microstructure changing processs when shearing. The yield features are studied for different dry density samples of the unsaturated soil. Dry density influences initial state, by determining the initial position of the yield surface, thus affecting the shearing behavior.3. General characteristics of soil-water characteristic curve (SWCC) were investigated. The soil-water characteristic curves of remoulded Guangxi and Hefei expansive soils with different dry density were attained by pressure plate tests. The results indicate that dry density has the effect on the soil sample structure (and pore size), which influences the soil-water characteristics. A equation was used to fit the data of SWCC, and the relation between fitting parameters and dry density was studied.