Study Of Predict Method About The Settlement Of Soft Ground Under Highway Embankment

Since the 1980's,Highway construction has entered rapid development period in our country. There are more and more high-grade highways built on the soft land area aside the sea. At the same time, it is very difficult to predict the settlement of embankment in the road's building and operation period. Some road surface split and some road and bridge became disconnected because of the big roadbed settlement. Ever more, the problem can't settle after several repairs, which leads to great waste in manpower and material resources.Therefore in order to accurately estimate the relation of settlement and time, it is necessary to take more research on the calculation of settlement of the soft ground, which have great directorial function in the construction of highways. Since Terzaghi advocated the principle of effective stress and concretion in 1923, substantial progress have achieved in the theoretical research of calculation of settlement of groundsill. Now, many calculation methods of the foundation settlement have developed, they can be divided into three types: one is analytical or theoretical formula method based on elastic theory and Terzaghi theory. The second type is numerical method based on Biot consolidation theory and constitutive model; the third type is experiential estimation method based on practical settlement and time.These methods complement each other and have become primary means in calculation of settlement of groundsill However, in the typical calculation of the settlement of foundation, additional stress incurring by loading is calculated according to elastic theory which has the same characteristics in semi-infinite space, the condensation of soil is decided by the condensation experiment of one-dimension and the settlement is calculated by adding results of respective layers. Obviously, it has not considered the nonlinear relation of stress and strain neither the influence of lateral displacement of the soil. Furthermore, it is difficult in selecting the modifying coefficient correctly when the geologic condition and load is different. As to the numerical analysis method, Different difficulties exist in distinguishing the constitutive model and ascertaining the model parameter. In the finite element analysis and handling some engineering measure there exist many problems that should be investigated further and optimized.The second part of this thesis analyzed the distortion characteristic of the soil when it is pressed, based on which a improved formula is established which suit for the rectangle area under the vertical even press and can consider the lateral distortion of soil. By calculating the engineering example, it can proved that the improved formula is acceptable in theory and the calculated result is close to true figure, which have great referenced value to practical project.The third part took further investigation in the constitutive model's distinguishing and the model parameter's ascertaining and some work were also donein the numerical analysis methods and problems met in the realizing of engineering measure in numerical analysis.The forth part compared the Biot finite element method with ordinary method.the author concluded that the Biot FEM can reflect the influence of lateral displacement more truly, calculate the settlement at every moment more suitably, and consider the progress of construction more easily.At last, several prediction methods of the final settlement of soft soil ground are introduced. Such as the Asaoka method, exponential method, hyperbolic method, three-point method. And an engineering case is presented, and the merits, drawbacks and applicability of the above methods are analyzed.