Sussex County, DE
GTA was retained to provide geotechnical engineering services for design and construction of slope stabilization measures for a 25-foot-high natural slope on the Nanticoke River. Slope instability was threatening residential construction near the top of the slope. This evaluation included subsurface explorations, laboratory testing and slope stability analyses to evaluate the landslide. The explorations included up to 40-foot-deep Standard Penetration Test (SPT) borings by hollow-stem auger and mud-rotary methods. Laboratory testing, including Direct Shear tests, was performed to evaluate peak and residual shear strength parameters of the native, overconsolidated soils, along with other soil parameters. Slope stability analyses were performed to evaluate the factors-of-safety against global slope failure. GTA also provided recommendations and assisted with development of slope repair drawings and specifications for increasing the stability of the existing slope by incorporating drains to lower the groundwater elevations, and bioengineered planting program and shoreline protection measures, such as revetment, groins and sills.