Inverse Analysis And Forecast Of The Post-construction Settlement With Drainage Consolidation Method On Soft Foundation

On the basis of practical engineering, design principle and method of control post-construction settlement of expressway on soft foundation using vacuum combined with surcharge preloading were presented in this paper. According to the field monitoring data, the conclusion of the regularity about the settlement, settlement rate, pore water pressure and lateral displacement can be drawn.When the FEM were used to analyze these problems, in order to simplify calculation, according to the equivalent transform relationship between sand-drain foundation and sand-wall foundation, the 3-D problems are transformed into the 2-D plane-strain p roblems, at the s ame time, t he r esistance and s mear were considered. Concerning the c onstitutive model, the double yield surfaces model of Zongze Yin combined with the modified Komamura-huang model was considered, and the dilation, contraction, visco-plasticity of soil could be considered together into the model, therefore it was suitable to the real soil characteristics. The damage theory was introduced, when the strength characteristics and variety rule of soil were taken into account.On the basis of Prof. Weibing Zhao's theory of sand drain primary and secondary consolidation and semi-analytic method of vacuum preloading sand drain foundation, simplified calculation method of post-construction settlement was researched. Consolidation calculation of partially penetrated vertical drain was analyzed and the result was introduced to calculate post-construction settlement. Foundation was divided into two parts: improved layer and underlying stratum, and post-construction was separated into three components, namely, primary consolidation settlement of improved layer, primary consolidation settlement of underlying stratum, secondary consolidation settlement of the whole layers. By the research of the Jing-Zhu expressway, it was found that primary consolidation settlement and secondary consolidation settlement of whole foundation layers were the major part in post-construction settlement. The conclusion was drawn that design method of controlling post-construction was feasible. As far as vacuum combined with surcharge preloading, it is an excellent method for controlling post-construction on the expressway's foundation.Aiming at the loading characteristic upon the expressway's foundation, it was found that the curve of computational settlement was simulated with the curve of measured settlement well at the beginning of construction, but not well at the end of construction, because the influence of the course about unloading and reloading were not taken into account. Under the circumstances, some research has been developed in this paper, coefficient of consolidation Cv, modified coefficient of decompression modulus k, modified coefficient of reloading modulus / were gained by inverse analysis, with the data of the prophase settlement. Using this gained data, the ultimate settlement and post-construction settlement could be forecasted, and the inverse analysis and forecast program was compiled. The forecasted values were compared with the measured values, and both were very much alike.