What Are Soil Nails (Ground Screws)?

A soil nail wall is a gravity composite soil structure in which an excavated slope or vertical cut is internally reinforced through the placement of closely spaced linear reinforcing elements. Reinforcing elements like ground screws are installed by placing them into the existing soil slope or new excavation. This adds strengthened soil nail slope stability for long-term earth retention.  

Soil nail drilling is performed in vertical steps, with construction starting at the top of the excavation and proceeding down. Once an excavated level is reinforced with soil nails, a permanent or temporary facing is applied to retain the soil. The resulting soil structure has nails placed to depth and of a sufficient density to ensure it can resist the forces imposed by the soil and surcharge loads. The failure modes that are analyzed to provide stability for a soil nail wall include sliding, bearing, and global stability failure modes.

There are two different types available:

    • Screw anchor nails

    • Grouted nails

Soil Nail Applications and Recommended Uses

Ground screws and soil nail systems are versatile, with a number of possible uses.

  • Earth Retention:

When installed in a closely aligned grid pattern, these systems can hold retention in one solid mass (depending on soil densities).

  • Tieback Wall Alternative for Temporary Excavation:

A tieback wall design differs considerably compared to the use of soil nails in that they are not tensioned. Compared to helical anchors used for tieback walls, there is no need to build pile and lag.

  • Slope Stabilization or Landslide Remediation:

Soil nails are used to reinforce failed slopes and walls in situ. Effective use calls for drilling A.B. Chance helical anchors beyond the reach of the failed slope. This is particularly efficient; because the use of this stabilization is created in situ, there is no need for removal and/or replacement of the failed soil.

  • Roadway Widening Under Existing Bridges:

The use of soil nails or ground screws can cut down on the number of construction steps needed when widening roadways under an existing highway bridge. When combining ground screws or earth screws with a shored permanent wall, there is no need for shoring.

Soil Nails from Intech Anchoring

Soil nails from Intech Anchoring are hollow, threaded, steel rods that can extend to any length in all soil and rock conditions to meet your project needs. The Intech Anchoring Magnacore® Soil Nail Wall system is used to stabilize slopes and structures at shallow or deep depths. This is a quick installation that combines drilling, placing, and grouting in one operation. This allows the system to be suitable for working in a limited space.

Thanks to the full-length thread and extension couplings, this system offers flexibility as it easily adjusts the bar length to the site requirements. This is especially useful if anchoring has to be performed in a confined workspace with limited headroom, which is usually the case in underpinning.

Self-Drilling Anchors for Soil Nailing

The Magnacore® SDA system offers self-drilling soil nails where the central hollow threaded reinforcement bar acts as both final reinforcement in the completed anchor and as the drill rod during installation. The SDA system is installed with sacrificial drill bits under a grout flush. In granular deposits in particular, the impregnation of grout into the surrounding ground significantly enhances the geotechnical capacity of the anchor. Large slabs of concrete and rock can also be readily drilled. These anchors work well as both tension and compression tiebacks and can be installed horizontally to meet any tieback or anchoring design criteria.

Features and Advantages

  • Ideal anchor system for unyielding ground conditions

  • Combines drilling, placing, and grouting into one step

  • Self-drilling system eliminating a cased borehole

  • Simultaneous drilling and grouting possible

  • Easy installation in all directions, including upwards

  • Suitable for working in limited space or height and difficult access

  • Simple post-grouting system

  • Hot-dipped galvanizing for corrosion protection

Soil Nail Technology

Retaining walls using anchored bars date back to the 1960s and earlier. In North America, soil nails were first introduced for temporary excavation support in Vancouver, BC, in the late 1960s and early 1970s. The first documented project in the United States was in Portland, Oregon, for excavation support of a hospital foundation. The maximum excavation depth was 45 feet. The soils consisted of medium-dense to dense silty fine sands. The work was reported to have been completed in 50% to 70% of the time required for conventional tieback construction and at a 15% cost savings.

In 1996 the U.S. Federal Highway Administration (FHWA) published its Manual for Design and Construction of Soil Nail Walls. This manual synthesizes research and past work in Germany, France, and current U.S. practice to form a guideline for soil nail design for highway works.

Today in the United States, the primary use of soil nail walls is for the temporary and permanent support of building excavations. Walls up to 75 feet tall have been successfully constructed. This application for soil nailing continues to grow due to the economic benefits it has over conventional tieback construction.

Soil nailing has been used for highway applications dating back to the 1980s. Soil nail walls up to 40 feet tall have been used on federal highway projects. With the development of the FHWA guidelines and promotion of this technique for highway works, the use of soil nailing will continue to grow.

To learn more about soil nailing systems, contact Intech Anchoring today.