Prediction of the Performance of a Geogrid-Reinforced Slope Founded on Solid Waste

Abstract

An investigation was undertaken to evaluate the integrity of a geogrid-reinforced steep slope subjected to significant differential settlements and seismic loading. The reinforced soil structure under investigation was constructed in 1987 in order to enhance the stability of steep landfill slopes at the Operating Industries, Inc. (OII) Superfund site, a hazardous waste site in southern California. The site is in an area of high seismicity. The 4.60 m high, 460 m long geogrid-reinforced structure was founded, along most of its length, on concrete piers located towards the front of the structure. However, as the back of the reinforced slope was founded on waste, the structure experienced more than 600 mm of differential settlements ten years after its construction. A geogrid experimental testing program was implemented to evaluate the performance of the reinforcements when loaded rapidly after a period of constant load. A finite element numerical simulation was performed to assess the integrity of the geogrid reinforcements when subjected to 30 years of additional differential settlements followed by the design earthquake. The maximum geogrid strains predicted for a sequence of expected static and extreme seismic loadings were found to be well below the geogrid allowable strain values, indicating that the integrity of the structure should be maintained even when subjected to large differential settlements and severe earthquake loads. The numerical results show that the critical reinforced zone (i.e., the reinforcement layers that are strained the most) that corresponds to different loading mechanisms (construction, differential settlement, seismic loading) occurs at different elevations within the reinforced soil structure.