Landfill Expansion Dynamic FEM Slope Stability Analysis, Babylon, New York

Overview: The Department of Environmental Control in Babylon, New York proposed design changes to a landfill expansion project. The proposal planned to reclaim an existing stormwater recharge basin by replacing it with hydraulic fill as to build the expansion on top. GeoStructures was retained to review the design changes for the proposed expansion. 

The original design utilized traditional leaching rings for stormwater management; however, lack of storage capacity led the design to change to an underground stormwater detention system (USDS) made up of modular polypropylene units called RainTanks. Since the USDS would be installed quite close to the toe of the 200-ft high landfill, the critical issues for the project were:

  • Large lateral earth pressures on the USDS tanks from the retaining walls and slopes which could exceed the strength of the tanks
  • Potentially reduced slope stability factors of safety
  • Potentially reduced factors of safety against liquefaction of the hydraulically deposited fill in the recharge basin

GeoStructures performed finite element method (FEM) analysis to develop an accurate determination of the lateral earth pressures on the sides of the USDS tanks. By running the FEM analysis, GeoStructures was able to optimize the design through revising the tank geometry and recommending minimum design strengths for the tanksthose of which were subsequently verified through material testing.

GeoStructures also performed dynamic slope stability, retaining wall analyses, and liquefaction hazard analyses for the project. The liquefaction hazard analyses were performed using traditional semi-empirical methods, as well as 2-D dynamic FEM analysis. In the dynamic FEM analysis, selected ground motions were run through the model to study the effects, and the resulting dynamic stresses and strains were then utilized as inputs for a dynamic FEM slope stability analysis. The factor of safety could be analyzed at each time step in an earthquake record to study the resulting deformation of the slope above the zone of liquefaction.

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