Dissertation
Dissertation > Industrial Technology > Building Science > Soil mechanics,foundation engineering > Various types of soil and foundation > Expansive soil and foundation

Experiment Study of Unsaturated Expansive Soil

Author XuFei
Tutor WuXiong
School Chinese Geology University (Beijing)
Course Geological Engineering
Keywords undisturbed expansive soils Soil-Water Characteristic Curve coefficientof permeability Shear strength
CLC TU443
Type Master's thesis
Year 2013
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With the undisturbed Yanji expansive soils, in this paper, we did three aspects ofresearch: Soil-Water Characteristic Curve (Short for SWCC), the permeabilitycoefficient of unsaturated soil, and shear strength. SWCC plays an important role inthe history of the development of unsaturated soils. Measuring SWCC is costly, timeconsuming and need high technical requirements, and the way of how to analyze andinterpret the experimental data are far more difficult than that in saturated soilmechanics. Research has shown that SWCC has an important significance in manyresearch fields, such as the shear strength, seepage, consolidation theory andconstitutive theory. SWCC of a soil can be used in the establishment of a number ofthe unsaturated soil parameters. This paper used the VJ Tech consolidation systemmeasured the SWCC of Yanji expansive soils. Five equations (Gardner model,Brooks&Corey model,Van Genuchten model, Fredlund tri-parameter model andFredlund quart-parameter model) are employed to fit SWCC. The coefficient ofPermeability of the unsaturated soil is predicted by the SWCC. And we did theunsaturated shear characteristics research with the shear strength experiment for Yanjiexpansive soils. The main achievements in this paper can be obtained as follows:(1) Between the drying curve and the wetting curve has significant hysteresis.It’s shown that the soils is easily wetting than drying and it’s a good medium forretaining water. The moisture content is reducing with the increasing of matric suctionin the SWCC curve. And in the Gardner model, we can conclude that the air entryvalue is about40kPa of the Yanji expansive soils.(2) According to the results of the SWCC curve, we know that the best effectiveis VG model and the better effective is the Fredlund model. The Fredlundtri-parameter model and Fredlund quart-parameter model is similar in the fitting result,so the assumption that the residual water content is zero is right.(3) The coefficient of permeability is higher, when the water content is higherand the matric suction is lower. There is a similar hysteresis form for both thevolumetric water content, and the coefficient of permeability, when plotted against matric suction. However, if the coefficient of permeability is cross-plotted againstvolumetric water content, the resulting plot shows essentially no hysteresis.(4) According to the fitting results and the equation, we deduce m=5.63127. It’shave an important significance on the relationship between shear strength andexpansive property of unsaturated soils.

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