Experimental Study And Data Analysis Of Loess Shrinkage

The loess plateau belongs to the arid and semi-arid regions. Continuous droughtcan lead to soil shrinkage deformation and shrinkage cracks. Shrinkage cracks have agreat effect on the engineering properties of the soil, such as reducing the soil strength,increasing the permeability and so on. When the loess slope existing cracks experiencessudden rain, the water will get into the soil quickly along the cracks, formingpenetration source at the cracks and increasing moisture content of the soil, which resultin a great impact on the stability of loess slope. Therefore, this paper carried out aresearch work on the shrinkage property and crack problems of unsaturated loess.Firstly, indoor dehydration shrinkage test for different initial moisture content anddry density of unsaturated loess samples was carried out to study the shrinkagedeformation characteristics of unsaturated remolded loess in the dehydration shrinkageprocess. The changing process of the loess shrinkage strain was measured and thechanging rule of loess shrinkage strain with moisture content was revealed. Theshrinkage curve of the soil can be divided into three stages: linear constant speedcontraction phase, deceleration contraction phase and stable period. The borders ofwater content were approximate4%and9%. Soil shrinkage change is mainly related tothe initial water content, and the soil density has a little effect on it. The higher theinitial water content, the greater the shrinkage change may be. The shrinkage strainchange has an exponential relationship with the initial water content, and expressionformula is obtained. The Soil shrinkage deformation mainly happens on the linear rateshrinkage stage. In order to evaluate the shrinkage deformation response to the watercontent changes, we define the shrinkage coefficient of soil and give suggestions on selecting suitable shrinkage coefficient.Secondly, in order to study the influence of sample size on test results, sampleswith different length to diameter ratio or same length to diameter ratio but different sizewere tested, basing on the theory that the soil swelling or dehydration shrinkage resultfrom the changes in moisture content was similar with the reaction of general materialto the changes of temperature and the existing constitutive model of loess. According tothe analysis results, sample line shrinkage rate did not change with the change of thespecimen size. The axial line shrinkage rate reflected the shrinkage characteristics ofsoil, and the linear shrinkage is the deformation characteristics of soil basic. Theexperimental results are not affected by the size of the sample.At last, in order to study the development of crack width during the shrinkageprocess of unsaturated loess, the crack width development process data analysis iscarried out basing the existing constitutive model of loess, using the aforementionedshrinkage coefficient value and considering the effects of moisture content range andcrack spacing. According to the analysis results, in the case of the same moisturechange in the soil, the crack width of the same soil crack spacing is same, and with theincrease of the crack spacing, crack width also increases in a good linear relationship.When the crack spacing is the same and the initial moisture content is different, thecrack width increases with the initial moisture content and shows a good linearrelationship. The main factors influencing the crack width are crack spacing and theinitial moisture content. The crack width formula under different crack spacing andinitial moisture content is obtained by curved surface fitting.