Experimental Study On The Drying Shrinkage Characteristics Of Expansive Soils

The expansive soil is a kind of special soil which expands when meeting water and shrinks when losing water, which exerts important influences on the safety of engineering structures. In recent years, researches both home and abroad have focused more on the swelling deformation characteristics of expansive soils meeting water or wetting, but the shrinkage deformation characteristics of expansive soils losing water or drying have not been paid enough attention to. However, in real engineering projects, the engineering geological problems and disasters caused by the shrinkage of expansive soils have been reported every now and then, and have also led to huge economic loss. Therefore the systematic mastery of volumetric deformation characteristics of expansive soils in the drying process has both theoretical and engineering significance to the prevention and reduction of disasters in the expansive soil areas.Supported by the Outstanding Youth Science Foundation (41322019) and the Natural Science Foundation of Jiangsu Province (BK2011339), this paper took expansive soils as the object of study, compared and analyzed both the advantages and disadvantages of different shrinkage volumetric measurement methods, systematically studied the volumetric shrinkage characteristics of expansive soils in the drying process and their influencing factors and restraining technologies through conducting a host of indoor tests, explored the evolution laws of the main mechanical properties in the drying shrinkage process of expansive soils, and also put forward a shrinkage model of expansive soils based on the theoretical analysis of the results. The paper has mainly obtained the following achievements: 1. Four main shrinkage volumetric measurement methods were analyzed and compared, namely, the direct method, the indirect method, the digital image processing technology and the laser scanning imaging method, and both the advantages and disadvantages of each method and their applicable conditions were pointed out as well;2. Based on the shrinkage characteristic curves, the influences of the soil composition, sand-containing volume and the initial compaction status (including water content and dry density) on the shrinkage characteristics of expansive soils in the drying process were studied, and the control variable method was also adopted to master the influencing laws of each factors on the shrinkage characteristics of expansive soils and their influencing mechanisms were clarified as well;3. The shrinkage restraining technologies of expansive soils were put forward, including lime-modification technology, cement-modification technology and the SWT-modification technology; through conducting a host of indoor tests and theoretical analysis, the restraining performances and the mechanisms of each technology were mastered;4. The anisotropy phenomenon was observed obviously in the shrinkage of expansive soils; through introducing shrinkage geometry factor, r, the shrinkage anisotropy of expansive soils was described quantitatively; and the influences of soil composition, sand-containing volume and water content on the shrinkage anisotropy of expansive soils were also clarified as well;5. Based on a large number of indoor shrinkage test results, a quadratic polynomial model was put forward to describe the relationship of void ratio and water content in the drying process of expansive soils; and it was found that the fitting of this model to the Pukou expansive soils was the most excellent, and following that were the GMZ bentonite and the Romainville expansive soil;6. Through conducting unconfined compression strength test and uniaxial tensile strength test, the changing laws of the unconfined compression strength and the tensile strength of expansive soils with the water content in the drying shrinkage process were studied, and the results showed that in the drying process of expansive soils, with the decrease of water content, both the unconfined compression strength and the tensile strength of expansive soils increased, and the increasing speed also rose correspondingly; besides they increased exponentially with the decrease of the water content, and there was also a linear relationship between the unconfined compression strength and the tensile strength; for expansive soils with different initial water contents, when dried to the same water content, the tensile strength rose with the increase of the initial water.