The Settlement Mechanism Of Soft Clay Roadbed And Study On Its Developing And Forecasting Method

The settlement forecasting of soft clay highway roadbed is a key problem in engineering. There are many characteristics of soft clay, such as high compressibility, bulky water content, low strength and bad hydraulic permeability, so the settlement of roadbed must experience evolvement, development and final stabilization. It has great theoretic significance and practical value in studying the developing law of settlement of soft clay roadbed and forecasting the future settlement which uses limited measured data and rational mathematic model.Firstly, through the deeply study of developing law and characteristics of soft clay roadbed settlement, the engineering properties of soft clay have been recommended and the conclusion has been obtained that the settlement developing experiences four stages. The four stages are occurrence, growth, stabilization and terminal, whose characteristics are discussed separately. Secondly, based on the stress strain relation and the common law of soft clay roadbed settlement, an idea has been put forward that the characteristics of consolidation settlement-time curve are similar with the S-type growth curve used in economic prediction. Then based on the S-type growth curve models, a variable-weight combination forecasting method has been presented with the idea of combination prediction, and a variable-weight combination S-type growing model has been established, which can forecast the settlement of soft clay roadbed at any time using limited measured settlement data. At the same time, in order to realize building online-model in engineering by computer, monitoring project situation and making control, the time series analysis method is also used in the modeling of the settlement development in this thesis. The best one-step forecasting calculation has been done by gradually disappearing memory method to estimate the model parameter recurrently, which can be applied in settlement forecasting project. Finally, the settlement calculation programs are developed in Matlab programming language, which are both applied in the coastal engineering practice. The final results indicate that the effect of the prediction by the two models are superior to other former models and the methods are so flexible that they offer effective and applied ways in forecasting the settlement of soft clay roadbed.