Research On Post-Construction Settlement Prediction Of Soft Ground Road Embankment Improved By DJM Pile

In order to enhance road embankment stability and control settlement deformation, DJM composite ground is widely used to reinforce the embankment constructed on soft soil. It has been proved in practice that the road overlaid on soft ground strengthened by DJM Piles has a less settlement after construction. Since the cost is relatively high, this method is only commonly used to enforce the soft ground beneath embankment near bridges, beneath culvert, or underpass structures. At present, some useful results of calculation theory and test research on the embankment deformation have been achieved; however, the characteristic of DJM composite ground is very complex; the mechanism of the stress-deformation theory of DJM composite ground has not been thoroughly understood yet; and the uncertain influence factors of design parameter are too many to be decided. So there still exits much disparity between theoretical result and measured result. As traditional design method cannot satisfy the need of predicting the highway post-construction settlement, when DJM Piles is applied in a freeway project, it is generally conducted as a study issue.Basing on the previous achievements, the writer has established the system of DJM composite ground under the flexible foundation, and systemically discusses its composition, meaning, as well as the roles of its different parts. The reinforcement mechanism of DJM composite ground, settlement deformation, distribution law of the pile lateral friction are comprehensively analyzed and summarized. Considering the pile stress deformation, the writer puts forward a method that combines the Geddes' solution with Boussinesq's solution to calculate the superimposed stress of DJM composite ground, and then uses the superimposed stress to calculate the settlement by layer-wise summation method.According to the practical foundation shapes, the consolidation models of the soil between piles and the substratum are built and solved respectively on the theory of Terzaghi-one dimension consolidation. The effect of each parameter on the consolidation of the DJM foundation is discussed in this thesis.Connected with the projects of highway DJM composite ground, the settlement of road embankment is calculated, using the method put forward in the thesis. The research also applies different settlement prediction models, and draws theoretical conclusions to compare with the in-site test results of DJM composite ground. The results of calculating settlement are well in agreement with the measuring settlement results.