Foundation Supportworks Products

Helical Soil Nails

Soil nailing is a method of earth retention that relies on reinforcing strands or members installed within a soil mass to create an internally stable gravity wall/retaining system. Soil nail wall technology began in Europe with use of the New Austrian Tunneling Method in rock formations in 1961. The technology then carried over to applications involving unconsolidated soil retention, primarily in France and Germany.

Soil nail walls were first used in North America for temporary excavation support in the late 1960’s and continued to gain recognition and acceptance during the 1970’s and 1980’s for higher profile projects including highway applications. Much of the soil nail wall research performed in North America was funded by the Federal Highway Administration (FHWA) and other state highway agencies during the 1990’s. Although helical piles have been used as tiebacks since the early 1950’s, helical soil nails are a relatively new alternative to their grouted counterparts.

Soil nail walls offer the following advantages over tieback walls as well as other top down construction techniques:

Helical soil nail wall installation

A helical soil nail typically consists of square shaft lead and extension sections with small diameter (6 to 8 inches) helix plates spaced evenly along the entire shaft length. The helical soil nail is installed by application of torque, similar to the installation of a helical tieback.

The helical soil nail is a passive bearing element, which relies on movement of the soil mass and active earth pressures to mobilize the soil shear strength along the nail. In contrast, a tieback is pre-tensioned to mobilize the soil shear strength around the helix plates. Excavation, soil nail installation and application of wall facing is completed in steps from the top of the wall downward.

Construction Methodology

Soil nail walls are constructed from the top down where the excavation proceeds. The construction sequence for a typical helical soil nail wall includes:

Helical soil nail wall installation

Nail Head to wall detail

For additional information, including technical product specifications, refer to the Supportworks Technical Manual

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