Field Study On Foundation Reinforced With Vacuum Preloading At Chongwan Section Of Huaihe-Changjiang Waterway

The Chongwan section of Huaihe-Changjiang Waterway is a burst period in history, the settlement of ground keeps going since the project built. It had ever been reinforced using different methods (eg. soil-cement mixing pile) in the history, however, the problem of settlement was not resolved in fundamentally. In addition, there exist the safety problem, as the required elevation is not achieved, and cannot keep the flood capacity of 12000 m3/s. In this study, some experiments of vacuum preloading were taken in-situ with the ground under the embankment. The main works in this paper are as follows:(1) The straight-line vacuum preloading and conventional vacuum preloading field test were used on the West in the embankment.The monitoring of vacuum degree, settlement, pore-water pressure and vane shear strength was conducted. The main reason of the loss of the vacuum and the effect of the straight-line vacuum preloading were discussed, then we concluded that the effectiveness of the pipe system instead of the sand cushion, and the validity and applicability of the use of straight-line vacuum preloading to deal with the embankment;(2) The compression parameters, consolidation yield pressure, permeability and coefficient of consolidation for different soil were obtained by consolidation compression test and consolidation penetration test; The influence of dissipation in the excess pore-water pressure were discussed with the in-situ permeability coefficient value, range of smear and smear area ratio, and then discuss the difference in measured data and calculation data;(3) The layer wise summation method for surcharge preloading and the method of calculating the vacuum preloading induced settlement proposed by Chai et al. are combined for proposing a method of predicting settlement induced by vacuum preloading, with considering the loss of vacuum degree, and compared with the measured data.