Civil Engineering Association

Road Embankment and Slope Stabilization

This report and the accompanying software are part of efforts to improve the characterization and analysis of pile-stabilized slopes using one or two rows of driven piles. A combination of the limit equilibrium analysis and strain wedge (SW) model technique is employed to assess the stability of vulnerable slopes before and after using driven piles to improve the slope stability. This report focuses on the entry of input data, interpretation of the output results, and description of the employed technique. In addition to a comparison study with a full-scale load test, the finite element (FE) analysis using a general-purpose FE package, “PLAXIS,” is performed to verify the results. The characterization of lateral load induced by slipping mass of soils can be accomplished using the modified SW model technique. The SW model for laterally loaded pile behavior is a new predictive method (recommended as an alternative method by AASHTO [2007]) that relates the stress-strain behavior of soil in the developing three-dimensional passive wedge in front of the pile (denoted as the strain wedge) under lateral load to the one-dimensional beam-on-elastic foundation parameters. Two failure scenarios are employed in the developed computer program to include pile stabilization for 1) existing slip surface of failed slope and 2) potential failure surface. The two scenarios evaluate the distribution of the soil driving forces with the consideration of the soil flow-around failure, soil strength, and pile spacing. The developed procedure can also account for the external pile head lateral load and moment along with the driving force induced by the sliding mass of soil. The developed computer program is a design tool in which the designer can select an economic pile size to stabilize slopes. In addition to the external lateral loads applied at the pile head, the presented research work determines the mobilized driving force caused by sliding mass of soil that needs to be transferred via installed piles to stable soil layers below the slip surface. The side and front interaction between piles and sliding mass of soil is one of the main features of this project. The work presented also evaluates the appropriate pile spacing between the piles in the same pile row (wall) and the spacing between the pile rows. The computer program provides a flexible graphical user interface that facilitates entering data and analyzing/plotting the results. The finite element analysis (using PLAXIS) was used to investigate the results. A field test for pile-stabilized slope is used to validate the results obtained from the finite element analysis and the developed technique.