Study On Engineering Properties And Elastic-plasticity Constitutive Model Of Soils Stabilized With Cement And Nanometer Silicon

Additives can be used to improve the engineering properties of cement-stabilized soil (CSS), for example, in the engineering, high-early strength, low permeability and retardation of CSS is needed. With the further studies on engineering properties, modified mechanism and work performance of CSS added various additives, CSS has been extensively applied in the ground treatment, slope protection, bracing foundation pit, injection and ponding engineering, etc. However, the use of CSS is restricted due to low strength and large deformation. In this paper, nanometer silicon as additive is applied in the CSS. Strength and deformation property, and its influence factors and variable rule of nanometer silicon and cement-stabilized soil (NCSS) are firstly studied; then economic feasibility is analyzed; finally an elastic-plasticity model is established to provide theory for the use of the NCSS in the civil engineering.Based on lots of laboratory tests, influence factors and variable rules of the NCSS compression strength are analyzed. The results suggest that nanometer silicon can greatly enhance the compression strength of CSS and there exists optimal nanometer silicon content. Through orthogonal tests, the paper quantitatively analyzes the magnitude of the factors influencing NCSS compression strength such as nanometer content, cement content, ratio of water and cement, curing period. On the basis of analysis on testing data, relations between the NCSS compression strength and cement content, nanometer content, confining pressure and curing period are respectively established and these relations can be used to estimate the NCSS compression strength. Guided by Price Theory in Economics, feasibility analysis on application of NCSS in the engineering is presented. Analysis results show that the costs of NCSS will lower than that of the common CSS on the condition of the same strength when the price of nanometer silicon drops to a certain value.Failure process of NCSS in compression is described, phenomena occurred in testing process are explained. Nonlinear constitutive models of NCSS on the condition of single axis stress respectively are established for the rising phase and descending phase of stress-strain curve, and selection method and suggestion value of the models are given. In light of lots of stress-strain relations, statistical laws and relations between failure strain, deformation modulus and confining pressure, compression strength are also discussed.On the basis of abundant datum and elastic-plasticity theory, a general three-dimension failure criterion for NCSS is proposed. Analysis results indicate that failure curves in meridian plane of low strength NCSS are lines, and the curves of high strength NCSS are parabola. Yield criterion is established on the assumption of failure points depicted with ellipse. An elastic-plasticity constitutive model for the NCSS is deduced by the use of the yield criterion, related flow rules and plastic work hardening rules. Proposed hardening modulus can be conveniently obtained according to testing data.Stress distribution, deformation property and settlement laws of cylinder samples in triaxialtests and single pile compound ground are obtained. By an engineering example, analysis shows that the settlement of NCSS piles is smaller than that of CSS piles on the condition of the same factors, and that the settlement of NCSS pile with high nanometer content is smaller than that of NCSS pile with lower nanometer content when nanometer content is in the range of optimal content.