Study For Settlement Calculation And Forecast Method Of Soft Soil Roadbed

The soft soil roadbed has large settlement and the post-construction settlement will last for a long time under load. There will be potential post-settlement that maybe made largish harm to traffic and transportation for high-grade highways built on soft soil foundation, so it is necessary to calculate and forecast soft soil roadbed settlement before treatment. There are many factors that influenced the soft soil roadbed settlement, and every factor varies with time, on the other hand the characters of soft soil are complex, so it is hard to ensure parameters of soft soil. Because of these, calculation and forecast post-settlement of soft soil roadbed exactly become hotspot and difficulty. Therefore, to study and find out new methods of soft soil roadbed settlement calculation and forecast have important theoretical and practical significance for our country's developing highway construction.In the first part of this paper the author summarizes methods of foundation settlement calculation and forecast in and abroad, and find out the localization of general calculation methods of foundation settlement when they are used to calculate soft soil roadbed settlement, and make a analysis to the method which take into account side distortion. In Skempton-Bjerrum method foundation establish settlement formula of considering the lateral deformation under the rectangular load, and confirmed the formula rationality through the conputation example.In the second part, the author analyzes influence factors of soft soil foundation settlement and find out relationship between settlement to factors on the basis of settlement observation data.The soft soil has rheological character, it is difficulty to calculate the settlement caused by rheology of soil, so engineers sometimes estimate final settlement according toobserving relationship between settlement and time. This paper discuss application of grey system theory in soft soil roadbed settlement forecast on the basis of analyzing soft foundation settlement rule, and introduce grey model into soft soil roadbed settlement forecast, establish settlement GM(1,1) the forecast model.Carry on the modelling forecast according to Baoan road and Beijingbead highway Lingshan experiment section settlement observation data,the forecast result and the actual result tally well, that confirmed the model's accuracy and the usability. But must point out that soft soil nature difference is very big and the influence factor also differs under different project condition.The gray forecast model still has project practice examination, and in different project practice application make the suitable revision to the model parameter according to different nature of soft soil of different local.