<p><p><figure id='attachment_3420' style='max-width:554px' class='caption aligncenter'><img class="wp-image-3420 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Cross-section diagram showing layout of soil nails to stabilize a landslide along U.S. Highway 26-89 in Wyoming." width="554" height="270" /><figcaption class='caption-text'> Typical proposed cross section (Turner and Jensen 2005; With permission from ASCE)</figcaption></figure></p><p><div><h2>Project Summary/Scope:</h2>The construction was to replace an existing roadway with a new roadway with wider shoulders. The road is located next to the Snake River. The project occurred in a 300‑meter stretch of the road. Cut and fill was not an option for two reasons. The first was because bank erosion from the river caused a landslide to occur in a 20-meter bank below the roadway. The second was because of a creeping landslide extending 450 meters above the roadway. A retaining wall system would have to be put in place in order to widen the road and to stabilize the landslides. A soil nail wall was chosen to be constructed below the roadway and an SMSE system with a soil nail wall as shoring was constructed above the roadway because of limited right-of-way. Observations from strain gages placed in the upper wall showed that a face failure had occurred. Three layers of welded wire fabric were used in place of using reinforced shotcrete for a temporary facing. It is recommended to use shotcrete for temporary facing in the future. The MSE wall was still able to be constructed.</p><p>Subsurface Conditions: There were three distinct different layers of soil found at this site, each with a varying thickness. The top layer varied between clayey gravel and clayey sand. The middle layer was a medium stiff to stiff, low plasticity clayey to silty gravel. The bottom layer was a very stiff to hard dark gray shale. Groundwater was encountered in 3 of the 17 borings, at depths ranging from 4.9 to 12.6 meters below the surface. No consistent pattern of groundwater elevation is apparent at any of the sections investigated. Later observations during drilling for soil nails showed that discontinuous pockets of perched water exist at this site, primarily in coarse-grained layers believed to be colluvial deposits.</p><p>Soil strength parameters were based on direct shear tests run by WYDOT the year before the project on the site soil. The lower soil nail wall had a height ranging from 1.8 to 3.0 meters with a nail length of 12.2 meters. The upper soil nail wall had a height of 4.0 to 7.6 meters with a nail length of 10.0 meters. Soil nail pullout capacities were predicted using guidelines from Byrne et al. (1998). The computer program SNAIL was used during the design process. Grade 420 steel bars with a diameter of 32 mm were used for the lower wall and 25 mm diameter for the upper wall. The drilled hole diameters were 176 mm. All nails were placed at 15 degrees below horizontal. The MSE wall was constructed on the bench and consisted of MBW blocks and galvanized metallic reinforcement with select backfill.</p><p>During construction, the soil nails were installed by inserting the bar into the grouted boreholes. If conditions were encountered where the borehole would collapse, casings were used to reinforce the hole and then removed after the nail was placed. The lower wall was 221 meters long with 308 nails spaced 1.2 meters vertically and 1.8 meters horizontally. The reinforced shotcrete was 215 mm thick. This wall was then buried beneath a structural fill. The upper wall was 226 meters in length and contained 418 nails spaced 1.7 meters horizontally and 2.1 meters vertically. The MSE wall covering the upper nail wall had a height of 7.6 meters and a facing area of 1,100 m².</p><p>The soil nail wall was constructed from August 1998 to December 1998. In the fall of 1999, the MSE wall was constructed. This case history is the first known document detailing soil nails being used to stabilize an active landslide.<br><h2>Complementary Technologies Used:</h2><strong> </strong>Mechanically Stabilized Earth Wall<br><h2>Performance Monitoring:</h2>Strain gauges were attached to select nails in both upper and lower walls to measure axial strain. Two inclinometers were installed to monitor ground deformation before, during, and after construction. Overall, deformation was found to be within an acceptable range. The project has continued to perform well.<br><h2>Cost Information:</h2>The final contract cost was 2.8 million dollars.<br><h2>Project Technical Paper:</h2>Turner, J.P. and Jensen, W.G. (2005). “Landslide stabilization using soil nail and mechanically stabilized earth walls: Case study.” <em>Journal of Geotechnical and Geoenvironmental Engineering</em>, 131(2), 141-150.</p><p><a href="http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282005%29131… Case History Prepared:</h2>November 2012</p><p></div></p></p>