Biaxial versus Uniaxial Geogrids for Deep Patch Embankment Repair: Fid-Bau Portal

Biaxial versus Uniaxial Geogrids for Deep Patch Embankment Repair

Perkins, Steve / Cuelho, Eli

Forest roads constructed in steep hillside terrain by cut and cast techniques may experience instability in the form of excessive subsidence leading to large cracks and differential movement along the roadway bench. The deep patch embankment repair with geosynthetics (DPERG) technique has been employed in the Western United States and generally involves a 1 to 2 m deep excavation that is backfilled with compacted granular soils and one or more layers of geosynthetic reinforcement. The design goal of a DPERG is not necessarily to eliminate future slope movement but to confine potential failure surfaces to a region of the slope well below the roadway bench and extending out to the slope face such that a failure surface does not extend up onto the roadway bench. This results in movement along the roadway bench that is more uniform and less disruptive to traffic. Many slope repairs using the deep patch method correspond to areas of repair that are relatively short along the alignment of the roadway, suggesting that effects from the ends of the repair might be important to consider. Historically, uniaxial geogrids have been used for repairs regardless of the length of the repair. This paper examines whether biaxial geogrids, which provide for a tensile strength in the direction of the road alignment, offer improved performance in a deep patch as compared to uniaxial geogrids. This examination is carried out using a three-dimensional finite difference numerical model of a deep patch slope repair, which uses direction dependent strength and stiffness properties for the geogrid to model uniaxial and biaxial materials.