Patterned Ground Anchors used for Slope Retention

Systems of ground anchors are increasingly used to support steep excavation slopes and stabilize landslides. These ground anchor systems are comprised of a pattern of post-tensioned tieback anchors and multiple, isolated anchor pads or beams; they are less steep than tieback walls and do not have a continuous face, or a structure that penetrates the potential sliding surface. This paper addresses systems that contain up to 200 anchors, with individual capacities of up to 2000 kN, that have been installed in geologic settings ranging from shale to crystalline bedrock, and the associated soils. Observations are presented from the alternatives selection process, the investigation, design, and construction phases, and monitored performance of recent highway projects in the western United States. Specific design issues include analysis for anchor location, size, and length, bearing pad capacity and racking during tensioning and testing, desirable lock-off load, and corrosion protection. Specific construction issues include construction sequencing, allowable tolerances, and coordination with other items of work.