Researches On Engineering Properties Of Expansive Soils And Stability Analysis Of Expansive Soil Side Slope

The researches on engineering properties of expansive soils and stability analysis of expansive soil side slope were carried out which were supported by the project that expansive soil side slope of Nan—Bai Highway. On the basis of researches outcome, the paper made the futher researches on engineering properties of expansive soils and failure mechanism of expansive soil side slope, put forward the stability analysis method and filling techniques which were applicable to expansive soil side slope. The paper's main contents and conclusions were as follows.(1) The swelling-shrinkage behavior of expansive soils was discussed. The explaining of swelling-shrinkage mechanism was discussed with the angle of tiny viewing. The study was carried out about the variation regulation of swelling force and swelling-shrinkage deformation which were two important aspects of the swelling-shrinkage behavior.(2) The researches on shear strength behavior of expansive soils were carried out. Direct shear test was used to research the variation regulation of the strength of expansive soils. The results showed that shear strength of expansive soils decreased sharply with increasing water content and the relationships between the logarithm of cohesive force, frictional angle and water content are linear. It was gained by trial study that the relation of total index of strength along with water content.(3) By analyzing the result of example, it was appropriate that the strength reduction FEM could be used for the stability analysis of expansive soil side slope. (4) The researches on failure mechanism of expansive soil side slope were carried out. By analyzing the stability of some embankment and excavation slope of Nan—Bai Highway with strength reduction FEM, it is showed that strength of expansive soil foundations decreased sharply when the water dip into the foundations, the deformation of the whole side slope would increase, eventually result in the failure of the slope if the embankment slope on sloped weak ground. For excavation slope, in addition to the strength of expansive soil foundations decreased sharply when the water dip into the foundations, another important factor that could influence the stability of the slope was swelling force which was produced by the variation of water content, the swelling force influence the stability of the excavation slope greatly.(5) The researches on filling techniques of the embankment slope which on the expansive soil foundations were carried out. It is the first time to carry on a calculation to the embankment limit height aimed at the horizontal angle (a) of the expansive soil foundations with strength reduction FEM, it is showed that relationships between the embankment limit height and the horizontal angle (a) are linear. Another study was carried out about stair treatment technique of the expansive soil foundations when the height of embankment slope was big and the angle of expansive soil foundations was big. The results showed that technique of breadth step excavation not only can lower the slope but also prevent the expansive soil foundations from water and kept stability of the slope. Therefore, it was an valid technique when filling embankment slope on the expansive soil foundations. The calculation method of embankment limit height and the stair treatment technique could provide a reference for revising and perfecting the《Specifications for Design of Highway Subgrades》(JTGD30-2004) .(6) By using the treatment techniques of breadth step excavation and spreading geogrid to the slope engineering of Tan—Bai Highway, it was appropriate that the treatment techniques could be used for keeping stability of the expansive soil side slope through stability analysis. Therefore, the treatment techniques were suitable for being used in the same kind engineering.