Rheological Model Of Soft Clay And Its Engineering Application

Soft clay is an extremely complex engineering material, it has complex engineering properties for specific substance components and complex structure. In the traditional research of soil mechanics, soil is generally presumed to be elastic or elastic-plastic body. But whether to be linear elastic or to be nonlinear plastic, its constitutional relation is only the function of stress and strain and has nothing to do with the time. In fact, the stress and strain of soil in nature is closely related to time, so the time element is necessary to be included in the constitutional relation of soft clay. Based on the elastic-viscoplastic theory, the constitutional relation which contains stress, strain and time is called rheological mechanics of soil. An increasing number of projects show that many geotechnical engineering failures are related to rheology of soft clay, therefore it has great theoretical value and practical meaning to study the rheological properties of soft clay.As the importance of constitutive relation of soil on studying soil mechanics, the rheological constitutive relation is also important for studying soil rheology. Therefore all kinds of traditional theories of studying the rheological constitutive model of soil are systematically summarized in the text firstly, then, the merits and demerits of theoretical model and empirical model analyses. According to rheological nonlinearity of soft clay, the text put forward a simplified rheological constitutive model of combining theories with experiences, the theoretical model is used to describe the linear part of rheology and the empirical model is used to describe the nonlinear part of rheology. The model is successfully used to describe the rheology of shanghai muddy clay later. Secondly, introducing the BP neural network and according to the creep data of laboratory direct shear experiment of jiangmen soil, the text build a network rheological constitutive model of jiangmen soil for its strong nonlinear mapping ability and fault-tolerance ability, which can avoid disadvantages of that traditional rheological constitutive models built under each level loading are impractical and a necessary complex constitutive equation is built in order to meeting the fact, then, the model is verified by the direct shear creep experiment of soil of shanghai. it has characteristics of considering more factors, high simulation precision and good generalization ability. Finally, according to difficulties and flaws of calculating and predicting the settlement of subgrade, the paper introduces finite element method which considers rheology of soil. By the MSC.Marc/Mentat software, the settlement of subgrade of loop freeway of Hangzhou is calculated under two schemes, one considers rheology of soft clay, another doesn't consider rheology of soft clay. The result shows that the calculation scheme of considering rheology of soil is more applicable to practical settlement law of subgrade. In calculating settlement of soft subgrade, especially post-construction settlement, the rheological properties of soft clay is necessary to be considered.