Prediction For The Soil-water Characteristic Curve Of Unsaturated Soils

More and more engineering accidents encountered are caused by soils inunsaturated state in actual projects, this cause people to pay attention to the theory ofunsaturated soil mechanics and its application. Soil-water characteristic curve(SWCC) refers to the relationship between the suction and water content inunsaturated soils. Beacuse SWCC reflects the hydraulic and mechanic properties ofsoils in unsaturated state, it is becoming more widely used in many fields includingpercolation theory and strength theory of unsaturated soil mechanics, thus it has apractical engineering significance to study SWCC. The methods to determinate theSWCC is normally classified into both direct and indirect measurements. Theconstraints of direct measurements are time-consuming and costing a lot. It usuallytake a few weeks even months to obtain a complete desorption and sorption SWCCby means of existing testing techniques, besides a high accuracy is needed.Conversly indirect measurements are more efficient and economic than directmeasurements, so people are more like to indirectly get the SWCC by using a model.On this basis, this thesis embarks from the prediction models of SWCC andcombines with the fractal theory, mainly done the following works:(1) The practical engineering significance of SWCC is analyzed and then itsmeasure methods are summarized. Meanwhile, the advantages and weaknesses ofeach method are commented.(2) The formation and development of the fractal theory are introduced andsome fractal models of SWCC are listed. The prerequisites, fitting effects and scopeof application for each fractal model are also evaluated.(3) According to the purpose of this thesis, we selected the soil specimens fromthree construction sites and measured the basic parameters of reshaped soils’properties. Using the high-precision apparatus (GEO-Experts stress-dependentSWCC pressure plate system) to acquire the SWCC of the reshaped soil the reliabilityof the testing results and data analysis may be improved.(4) Within the partical size range for the test soils, we measure the particle-sizedistribution in terms of volume by using a laser scattering test. Let me assume thateach soil density is constant, and thus the particle size distribution in terms of volume can be converted into the particle-size distribution in terms of mass. By choosing themost appropriate fractal model, we estimate the fractal dimension and get the SWCCof each test soil.(5) Comparing the experimental results with the prediction conclusions from thefractal model, the applicability of the model is analyzed to make recommendationsfor practical engineering application.