Study On Deformation Characteristics Of Ning-ming Unstaturated Expansive Soil

Expansive soil is a kind of special unsaturated clays featured with the characteristic of swelling-shrinking, fissure character and over-consolidation. Swelling after absorbing water, shrinking after water loss are typical characters for expansive soil. For many years lots of researchers are devoted to the study on its deformation characteristic. However, because of the problems such as variety of parameters, complexity of test, difficulty for parameter selection, the current constitutive models of unsaturated expansive soil are difficult to be applied in the practical engineering. To be convinient for developing the analysis of slide and collapse regulations of expansive soil cuttings'slopes in expressway from Nanning to Youyiguan, the systematical research on the deformation characteristics of Ning-ming unsaturated expansive soil was carried out in this paper, from the aspects of stress-strain-moisture content (saturation) and stress - strain - suction respectively, and practical constitutive model was discussed and established.Firstly, by analyzing the test results of swelling under loading and contraction without loading, the regulation for the influence of initial moisture content and pressure, the initial moisture content and density to the characteristic of swelling and contraction of Ning-ming unsaturated expansive soil was obtained. And the corresponding relationships of the swelling capacity under loading and the vertical shrinkage rate during contraction with process moisture content were established.Using the advanced GDS systems in K0 consolidation test, lateral pressure coefficient of Ning-ming Hui-bai, Hui-hei expansive soil was obtained, the defect that K0 coefficient was mostly determined as fixed value based on experience in projects was made up for. At the same time, the variation law of K0 coefficient changed with moisture and confining pressure was analyzed, and the function expressions were established, which provide the basis for determination of the Poisson's ratioμ.In the same way, with the operation of the tests by GDS systems, elastic modulus E for Ning-ming Huibai and Huihei expansive soil was got, and Poisson's ratioμwas indirectly calculated according to the existing relations betweenμand K0, which solved the problems of the variety of parameters for constitutive models, complexity of tests, difficulty to parameter selection well for current unsaturated expansive soil constitutive models. The analysis of the two deformation parameters E,μchanged with the confining pressure and moisture content was done, and the law that E decreases with the increase of moisture decreases, increases with the increase of confining pressure increases, andμincreases with the increase of moisture content and confining pressure increases. Therefore the function expressions of E andμwith moisture content and confining pressure were established.Finally, based on the saturated soil ideal elasto-plastic constitutive model, according to the research results of deformation parameters from tests, the deformation and strength parameters in models are expressed as functions with confining pressure and moisture content. From the aspect of the stress-strain- moisture content (saturation), project practical constitutive model of the unsaturated expansive soil are established. At the same time, by the application of the research results of special deformation of K0 consolidation, from the way of stress-strain- suction, a one-dimension constitutive model of Ning-ming expansive soil under one-way loading was be put forward as a trial.