Three Integral Constant Determination Methods and Their Applications to Subgrade Settlement Grey Prediction Model

In this paper, three integral constant determination methods are proposed. First, the first point of modeling data sequence is used. Second, the last point of modeling data sequence is used. Third, the minimum point of fitting error in modeling data sequence is used. According to the above methods, six-step forecasts are respectively made by using six-group subgrade settlement observation data of Shaohuai expressway. The method of selecting integral constant is proposed by comparing and analyzing the predication results. Meanwhile, smoothing test for part of data is made in predication. For the two-group data which are not satisfy smoothness condition, cumulative settlement is used to build subgrade settlement grey prediction model, and the prediction effect was significantly improved.