Failure mechanisms and stability charts for embankments on soft clays improved with deep mixing columns.

摘要

Deep mixing columns (DMCs) are commonly used as a ground improvement method for embankments supported on soft soils. The deep mixing column (DMC) method has several advantages, including the possibility of constructing high embankments, relatively fast construction, and design and construction flexibility. The current technology allows the construction of DMCs with greater lengths and diameters. However, the stability analysis of this type of embankment-foundation system with DMCs remains challenging.;This research applied the finite difference method (FDM) to study the stability of embankments supported on soft clays improved with deep mixing columns. The commercially available software FLAC was used in the analyses. Preprocessing codes were written to create the finite difference grids and assign the material properties to reduce model preparation time and effort. Results from FDM for selected cases were compared to the results of other methods.;This research identified and characterized the possible critical failure modes of the stability problem of embankments on soft clays supported on DMCs, for both individual columns and overall collapse. The individual DMCs might fail in shearing, bending, or tilting mode, depending on factors such as column location, column strength, and embankment height. It was found that the embankment-foundation system may fail in one of three different modes of overall failure: embankment slope failure, foundation failure, and collapse failure. The embankment slope failure was identified as occurring within the embankment, with no failure of DMCs. The foundation failure was related to the failure of the DMCs. The collapse failure was described as a special case of the foundation failure, in which all columns failed by tilting.;Some factors were found to have little or no effect on the factor of safety of the problem for the conditions studied, including the embankment width, DMC diameter and spacing (when using the same improvement area ratio), and the soft soil thickness (for fixed-type columns). In contrast, some other factors were important to this problem, including the DMC strength and embedment, and improvement area ratio. This research also found that the most efficient design in terms of stability is the one in which all DMCs have the same strength, are located under both the embankment slope and the remaining part of embankment, and are of the fixed type. From the FDM results, a series of stability charts were created to assist in preliminary design and analysis of the problem in practice.