Experimental Study Of The Influence Of Clay Content On Mechanical Properties Of Unsaturated Soil

At present, the engineering properties of unsaturated soil have become a hot topic in the modern international field of soil mechanics. The mechanics properties of unsaturated soil are very different with the classic soil mechanics, and the engineering properties are more complex. The application instances of the unsaturated soil theory to solve engineering problems are still very few in realities, as the study of unsaturated soil are at the preliminary stage now. So, it is very necessary to study the engineering properties of unsaturated soil.In this paper, through the combination of direct shear tests and the soil water characteristic curve tests of soil samples at three different clay contents, the shear strength parameters characteristics of unsaturated remolded soil was explored. As to provide theoretical basis for engineering practice, the variation laws of shear strength with the change of clay content and water content of unsaturated soil are analyzed, and the influence of matrix suction of it is studied as well. The following are some main work and conclusions made from the paper:(1) The basic theory and the development history of unsaturated soil mechanics are introduced, and the research status of shear strength and soil water characteristic curve of unsaturated soil are summarized. Thus the beginners can have a preliminary understanding of the unsaturated soil theory.(2) Through mixture of the existing mucky clay and sandy silt, we have three kinds of representative soil, which have obvious difference in clay content, including clay, silty clay and clayey silt.(3) Through direct shear test results, we found that: the cohesion force increases initially then decreases with the increase of water content, and the water content of inflection point in consolidated quick shear test is smaller; the internal friction angle increases with the increase of water content, and the results in consolidated quick shear tests get larger than un consolidated quick shear overall.(4) Through comparison of test data, we found that: Under the same water content, the higher the clay content of the soil, the greater the cohesion force and the smaller internal friction angle. But the influence of clay content on variation of the cohesion force and internal friction angle with the water content change is not obvious. In consolidated quick shear tests, the sensitivity of the variation of the cohesion force and internal friction angle with water content reduces. Under the same vertical stress, the shear strength of the three kinds of soil have obvious difference. The higher the clay content, the smaller the shear strength, which is more obvious in consolidation process.(5) From the soil water characteristic curve test results, we found that: the shear strength increases with the increase of matrix suction, and the greater the vertical stress, the more obvious increase of shear strength, which is almost the same in three kinds of soil. Under the same vertical pressure, soil shear strength has greater increase, and more obvious affected by the matrix suction, in unconsolidated quick shear tests.