<p><p><figure id='attachment_2626' style='max-width:696px' class='caption aligncenter'><img class="wp-image-2626 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Cross section diagram showing screw-in soil nails." width="696" height="405" /><figcaption class='caption-text'> Screw-In Soil Nail Wall (Figure from www.abchance.com, courtesy of CHANCE® Civil Construction)</figcaption></figure><h2>Basic Function</h2>Screw in Soil Nailing uses a helical soil nail to insert passive inclusions into the ground as a temporary or permanent earth retention system.<br><h2>Advantages:</h2><ul> <li>Quick construction</li> <li>More cost effective compared to alternate technologies.</li> <li>Can be constructed with lighter equipment and in less space than other systems.</li> <li>Can withstand large deformations.</li> <li>Easily monitored and tested.</li></ul><h2>General Description:</h2>Soil nailing is an in-situ soil reinforcement technique wherein passive inclusions (soil nails) are placed into the natural ground at relatively close spacing (3 to 5 ft.) to increase the strength of the soil mass. Helical soil nails consist of 1.5 inch square solid steel shafts, on which steel bearing plates or helices are welded at regular intervals. Being a true helical shape, the helices do not auger into the soil but rather screw into it with minimal soil disturbance.<br><h2>Geologic Applicability:</h2><ul> <li>Work well in sands, gravels, silts, and clays.</li> <li>Soils with large boulders or cobbles are not suitable.</li> <li>Dense gravels and stiff clays will reduce penetration and are not preferable.</li> <li>Soils that are corrosive or prone to liquefaction or collapse when water is present are not suitable for the technology.</li> <li>A high groundwater table should be drained if the forces are too great. Water will decrease slope stability.</li></ul><h2>Construction Methods:</h2>Helical soil nails are installed using drill equipment with sufficient torque output. The drill is often attached to a backhoe, skid loader or trackhoeThe steel used to manufacture the nails is a high-strength alloy that is specifically formulated to resist the installation stresses associated with the high torque applied to the nails during installation. The spacing of the helices is a function of the helix diameter, and is typically about 3.6 times the helix diameter. If the wall is permanent, shotcrete or precast or cast-in-place concrete facing panels are installed after the soil nail wall is completed.<br><h2>Additional Information:</h2>Nail capacities are in the range of 20 to 25 kips each. Soil nailing is recently starting to be used more often in mountainous terrain. Launched soils nailing is a relatively new technology. Obstacles restricting the spread of the use of the technologies include the lack of simple, comprehensive, and reliable analysis and design procedures, proprietary technologies, and the need for specialized equipment. The technology has similar or lower costs than its competing technology, drilled and grouted nails.<br><h2>SHRP2 Applications:</h2><ul> <li>Roadway and embankment widening</li></ul><h2>Example Successful Applications:</h2><ul> <li>West Slope Reservoir Soil Nail Wall – Portland, OR</li> <li>Virginia Historical Society South Wing Addition, Richmond,VA</li></ul><h2>Complementary Technologies:</h2>Can be supplemental technology or used alone. Screw-in nails are typically used alone in places difficult to access or for small areas. Can be used with tiebacks or anchors and an SMSE Wall System.<br><h2>Alternate Technologies:</h2>Drilled/grouted and hollow bar soil nailing, Shoot-in soil nailing<br><h2>Potential Disadvantages:</h2><ul> <li>Technology requires skill and expertise and specialized equipment.</li> <li> Shallow excavation depth.</li> <li> Requires constant monitoring during construction.</li> <li> Inability to construct in sites where excessive drainage would be required, areas with soft clays, areas with freezing and thawing, expansive soils, soils with cobbles or boulders, and areas adjacent to structures or utilities sensitive to settlement.</li></ul><h2>Key References for this Fact Sheet:</h2>Collin, J. G. and Cowell, M. (1998). Soil Screw Retention Wall System Design Manual, Hubbell/Chance, Centralia, MO.</p></p>