Gray Forecast And Back Analysis Of Final Settlement Of Soft Foundation

Along with the development of country capital construction, more and more projects such as highway, airdrome run way, etd. were built in the area of soft clay, these projects require the settlement after construction completed definitely. However, in the existing design criterion, the calculation methods which base on one-dimensional consolidation theory can take into account the additional settlement caused by the lateral displacement that generated by the plastical flow of the soft foundation. It leads the calculation final settlement to be less than the actual settlement which leads the settlement after construction completed to be on the big side, and affect the project quality. So, it is possessed of great engineering meaning and theoretical value to improve the existing methods which are used for calculating the sefflement of the soft foundation.This paper which relies on the research of the test section of the soft foundation of the Thang-Zhao highway. Through analyzing the in-situ datum such as total settlement, layered settlement, lateral displacement and pore water pressure, we mastered the actual deformation behavior of soft foundation, and specially approved the chronicity of the lateral displacement in the soft foundation.Because of the complexity of the soft foundation plactic flow, it is much difficult to calculate the additional settlement caused by the plactic flow well and truly. So, the engineers often forecast the final settlement basing on the measured settlement curve. The general methods to forecast the soft foundation final settlement which base on the measured settlement curve are exponential curve method, logarithmic curve method, etc. The gray theory is used for forecasting the soft foundation final settlement in this paper, and the cubic B-spline function is used to make the original datum to be same spatio-temporal, and the buffered softening arithmetic is used to eliminate the infinite increase of the gray forecasting model to increase the forecasting precision. Through the compare we can draw a conclusion that the gray forecasting precision is the best, the exponential curve method is the second best, and the logarithmic curve method is the worst.The methods above all need the foundation having a long preloading period. But, to the general projects, because of the time limit, sometimes it can get the long period of measured settlement data, which will affect the veracity of the forecast result. In this paper, based on the gray forecasting final settlement, two parameters K and ~ of the Dun can-Chang model were back analyzed through two-step optimization back analyses using the FEM method. The FEM analysis was carried using back analytic parameters, it is proved that the parameters got through the methods shown above are of reliability We can believe with reason that as long as we accumulate a number of data, we will have the possibility to use these datum to make more exactly forecasting result of the final settlement of the soft foundation in the similar projects in the future through the FEM method.This paper is based on the research of the test section of the 8-kilometers-long soft foundation of the Zhang-Zhao highway.