<p><p><figure id='attachment_3418' style='max-width:630px' class='caption aligncenter'><img class="wp-image-3418 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Arial view of the completed soil nail wall, River Road Widening and Realigning, Pima County, Arizona." width="630" height="463" /><figcaption class='caption-text'> Arial view of the completed soil nail wall. (© 2011 Google)</figcaption></figure></p><p><h2>Project Summary/Scope:</h2>A soil nail wall system was used by the Pima County Department of Transportation (PCDOT) to stabilize and retain two steeply sloping bluffs up to 18 meters high in an effort to widen and realign part of River Road.</p><p>During construction, the contractor encountered a seam of dry loose sands, gravels and cobbles. Vibration of the drilling equipment caused the loose materials to ravel from behind the previously installed wall sections. It was decided to build a berm against the exposed section of the wall and water soak the berm. This allowed the development of enough apparent cohesion to complete the installation of the nails and excavate the berm to the next bench level until more competent material was encountered. The voids were later filled with a cement, sand and fly ash grout mixture.</p><p>Site accessibility impacted the design and construction in two ways. The first was that limited site accessibility prevented a more refined field investigation. This resulted in an overly conservative design. The second was limited construction access due to the proximity of the project next to apartment buildings.</p><p>Subsurface Conditions: The site was inaccessible to drilling equipment. Only one exploratory boring was completed at the site, and another boring was drilled on an adjacent bluff. Based on the results of the field and laboratory tests, the approximate geologic profile at the site appeared to be stratified with layers of varying thickness consisting of slightly- to heavily-cemented silty sands, gravels, and river-run rounded cobbles, with possible seams of loose sand, gravel, and cobbles. The SPT N‑values</p><p>were typically greater than 20. The following soil parameter values were assigned: effective cohesion of 24 kPa, effective friction angle of 33 degrees, and total unit weight of 18 kN/m³. The site was found to have low to no corrosion potential.</p><p>The soil nail system was designed in accordance with procedures described in <em>The Manual for Design and Construction Monitoring of Soil Nail Walls</em> (Byrne et al. 1998). The soil nail walls were nearly vertical and ranged in height from 2 to 3 meters at their ends to more than 17 meters at their highest point. The west wall was 130 meters in length and the east wall was 156 meters in length. Titan nails were used. The design utilized nine rows of variable diameter, hollow bar nails of variable lengths (4.9 to 15.2 meters) installed at an inclination of 15 degrees on a 1.8 by 1.8 meter grid. Where the soil nail wall supported an apartment swimming pool, the top row of nails was inclined at 30 degrees in order to avoid hitting the pool substructure. Weep holes, vertical drains, and drain strips were used to allow for adequate drainage. The design of the shotcrete construction facing was checked for punching shear and flexure in accordance with Byrne et al. (1998). Construction of both walls proceeded concurrently.<br><h2>Complementary Technologies Used:</h2>Reinforced concrete cantilever retaining walls<br><h2>Alternate Technologies:</h2>The Altamira Apartments are located on top of a bluff west of an access road leading from River Road to the apartment complex. The original plan proposed using a conventional reinforced concrete retaining wall system. Excavation for the retaining wall would have forced the apartment to relocate a swimming pool, recreation center, and an apartment building. Because of high property values in the area, the costs of relocating these components were prohibitive. The soil nail wall system was used to preclude the need to relocate major components of the Altamira Apartments.<br><h2>Performance Monitoring:</h2>Two 20‑meter long inclinometers were installed, one behind each wall. Measurements were taken before, during, and after construction. Survey targets were mounted on potentially impacted structures and were regularly monitored before, during, and after construction. Nails heads on the wall were monitored during construction. All potentially impacted structures were inspected inside and out prior to construction. Any observed cracks were photographed during this inspection. During and after construction the cracks were monitored and the buildings were inspected for any potential signs of new disturbance. The measured movements were well within acceptable deflection limits.<br><h2>Project Technical Paper:</h2>Nowatzki, E.A. and Samtani, N.C. (2004). “Design, Construction, and Performance of an 18-meter Soil Nail Wall in Tucson, Arizona.” ASCE Geotechnical Special Publication No. 124, Proceedings of GeoSupport 2004 Conference, Orlando, Florida, pp 741-752.<br><h2>Date Case History Prepared:</h2>November 2012</p></p>