Observational Approach Used for Slope Stability during Surcharging of Municipal Solid Waste and Soft Soils

This paper presents a case history of a recently completed portion of an ongoing ground improvement project in Northern New Jersey. The site is a former landfill underlain by soft, weak and compressible natural sediments. The project involved the design and implementation of a ground improvement program (GIP) consisting of dynamic compaction (DC) of the municipal solid waste (MSW) followed by implementation of a surcharge program to overconsolidate the MSW and the organic soils and to pre-consolidate the underlying soft varved clay soils. The heterogeneity of the MSW and the soft nature of the various natural strata made the conventional deterministic methods problematic and somewhat unreliable. Due to large variations in the published shear strength properties of the MSW and the inability to predict the strain compatibility between the compacted waste and the natural soil deposits, an observational method was implemented. As a result of constant field observations and measurements, large shear deformations were identified in a localized portion of the site that were subsequently mitigated. Removal of the surcharge fill, combined with installation of wick drains to accelerate the consolidation of the soils and improve their shear strength, enabled filling to continue safely.