Study Of The Characteristic Curves For Unsaturated Loess

Unsaturated soil is the presence of matric suction that results in a material that is complicated to understand its behavioral characteristics. In order to reveal and analyze the related properties of partially saturated soil, a large number of tests and theoretical studies have been carried out by scholars. In these studies, two types of characteristic curves have been used to understand the behavioral characteristics for unsaturated soil, which referred to soil-water characteristic curve (SWCC) and suction stress characteristic cure (SSCC). The SWCC is defined as the relationship between suction and water content (or degree of saturation) for the soils, which is an important topic in the research of unsaturated soil. The SSCC, which is one of the basic approaches for describing the stress state of unsaturated soils, revealed the relationship between suction stress and matric suction (or degree of saturation).By means of the15bar pressure plate apparatus of Soil Moisture Equipment Corporation, a series of soil-water tests for Lanzhou loess were conducted to study the properties of two kinds of characteristic curves (SWCC and SSCC). Based on scientific interpretation and analysis of test data, this thesis analyzed the performance characteristics and discussed the influence factors (i.e. initial densities, initial water contents and particle size fractions) and relationship of two kinds of characteristic curves in unsaturated loess. The main contents focused on the following aspects:(1) The water content and matric suction of remolded Lanzhou loess specimens were examined using the pressure plate apparatus based on axis-translation technique. The soil-water behavioral characteristics of different initial densities, initial water contents and particle size fractions were analyzed. After that, the water retention capacity of unsaturated loess under different initial conditions was also discussed.(2) The fitting parameters of common soil-water characteristic curve equations were obtained by fitting the test results. In addition, the fitting precision of two equations was compared for unsaturated loess. At the same time, with analyzing the changing regularity of fitting parameters among each test, the mechanism of physical states and characteristics for unsaturated loess was discussed from the point of macroscopic and microscopic views.(3) The suction stress was derived by analyzing the inter-particle force. Based on measured data, suction stress was calculated according to the method proposed by Lu. And then suction stress characteristic curves were evaluated by using the van Genuchten (1980) model to fit the suction stress. The curve-fitting parameters were obtained using least squares regression analysis, and the influence mechanisms of initial densities, initial water contents and particle size fractions were analyzed by analyzing the changing regularity of fitting parameters among each tests.(4) According the analysis of whole performance for the two kinds of characteristic curves among all soil moisture retention tests for unsaturated loess, the relationships between the two characteristic curves were estimated. Based on the series of tests, this thesis aims at understanding the characteristics of unsaturated loess by analyzing the performance, discussing the mechanism and investigating the relationship of the two characteristic curves.