Effect Of Void Ratio And Stress State Controlled Individually On Drying-Wetting Soil Water Characteristic Curve

Soil water characteristic curve(SWCC) is a graph showing the relationship between soil suction and moisture content, reflecting the relationship between energy and its mass or volume of water phase in unsaturated soil, affecting penetration, deformation, strength and other characteristics of unsaturated soil, and it is an important tool to describe the properties of unsaturated soil.But,there are also great differences between SWCC measured generally by lab test and the actual situation which mainly reflected in the state of stress of soil. Compacted soil samples were usually adopted in the traditional testing methods, and the samples suffered net mean stress is zero in test. But the soils generally under state of certain non-zero net mean stress in the actual geotechnical structure. Previous studies has pointed out that the stress state is the influencing factors of SWCC. However, some scholars believe that the different stress will lead to different void ratio, and the sample volume will be affected when the matrix suction is applied or removed, thus affecting the void ratio; Therefore, the void ratio directly influence the SWCC. Visible, on the effect of stress state on the SWCC, the focus on the debate is, whether it is the direct reason, or because of void ratio caused by the change of stress and suction is the direct cause, but only indirect cause of stress.In this paper, the research work is around this problem. In the basis of Introducing the effect of SWCC on the research status by the void ratio and stress state and summarizing several commonly used determination methods of SWCC and its influence factors, Two groups of SWCC test(three samples) designed specially are carried out in order to clarify the void ratio and stress state which is the essential factors affecting SWCC. In the two experiment, one group of drying and wetting test be carried out under the sample in the same vertical stress and different void ratio; another group of drying and wetting test be carried out under the two sample keep the same void ratio all time by adjusting the vertical stress of sample(i.e., the vertical stress is different).The main research results of this thesis are as follows:(1) The influence of matrix suction on the void ratio: in the drying process, the void ratio decreases with the increase of matric suction; in the wetting process, soil rebound and the void ratio become larger with the decrease of matric suction; the void ratio of the sample can not return to the status of starting point of the drying when wetting process is completed.(2) When the void ratio is different, there is also a great difference of SWCC even if the vertical stress is the same. The void ratio of the sample at the start of the drying bigger, the smaller is the intake value; the smaller the initial void ratio, the greater is the air entry value, and the better is the capacity of water holding of the sample.(3) There are almost no impact of the curve of the drying and wetting by the vertical stress when keep the same void ratio between samples.