Investigation On The Subgrade Deformation Due To Widening Expressway On Soft Groundwork

In the widening of expressways constructed on soft groundwork, the different settlement between the new and old embankments occurred commonly. A lot of enginerring attempts, aiming at overcoming road engineering problems from the different settlement, were carried out at home and abroad. However, the theoretical insight on overcoming different settlement still lag behind the related engineering practices due to lacking the corresponding systematic investigation. Based on the achievements of the widening made at home and abroad, the investigation on interaction mechanism and deformation of the new and old embankments was made in the work.Firstly, according to a given constructing widening expressway, the laboratory tests for the soft soil and the composite foundation piles were completed. Through the test results, the mechanical parameters of the soil and piles were obtained for the numerical modeling calculation and analysis.By means of the calculation, the einforcement effect of the new embankments treated by different techniques, including surcharge preloading, separating wall, Dry Jet Mixing (DJM) and light embankment, was analysized comparatively. The effect of the different treatment techniques used in the old embankments on the deformation of the new and old embankments was analysized comparatively too.The sensitive factors for controling the differential settlement were determined approximately. The optimization method was put forward for the expressway widening wih the composite foundation.The mechanism analysis of controlling different settlement by paving geogrids along the joint area between the new and old embankments was made, with the change of the locations, numbers and elastic modulus of geogrids. The optimization mode for paving geogrids was given.The scheme for controlling different settlement with the composite foundation of prefabricated piles was studied. According to the function mechanism of composite foundation, it was pointed out that, as the depth of soft soil was more than 15 meters, the composite foundation of prefabricated piles was obviously advantageous in expressway widening.Some investigation reults of the work was apllied to the expressway widening.