Estimation of the post construction settlement of the ground improved by preloading drainage is one of the most critical problems. Based on the consolidation theory of ground with vertical drains under the condition of equal vertical strain

approximate theory settlement curve calculation method is put forward. The least squares optimization method is used to best fit the theory settlement curve with the measured settlements and to determine total primary settlement and average consolidation degree

consequently post construction settlement can be estimated. The method is applied to two cases histories of ground with vertical drains improved by vacuum preloading and surcharge respectively to predict post construction settlement. It is verified that the method is applicable to engineering.