<p><p><figure id='attachment_3412' style='max-width:783px' class='caption aligncenter'><img class="wp-image-3412 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph showing Deep mixing method block treatment gravity wall at intersection of Air Cargo Road and Taxiway B, Oakland, CA." width="783" height="423" /><figcaption class='caption-text'> DMM block treatment gravity wall at intersection of Air Cargo Road and Taxiway B (From Yang 2003).</figcaption></figure></p><p><h2>Project Summary/Scope:</h2>As part of the Oakland Airport expansion, a new grade separation structure was needed at the intersection of Air Cargo Road and Taxiway B. Block-type DMM treatment was used to create permanent gravity retaining structures to allow raising Taxiway B a maximum of 8 feet above existing grade and to lower Air Cargo Road a maximum of about 15 feet below existing grade. The DMM structures also served as a temporary shoring system during construction. At completion of the wall, approximately 45,000 cy of soil-cement were mixed.</p><p>Subsurface Conditions: 10- to 15-foot-thick layer of artificially-placed dredged, very loose to loose sand overlying Young Bay Mud (very soft to soft silty clay) about 3 feet thick; this clay layer was absent in parts of the site. Competent medium stiff to very stiff clays and medium dense to very dense sands of the San Antonio Formation were encountered beneath the sand fill and soft clay layers. Ground water levels varied from 5 to 10 feet below the existing ground surface.</p><p>The designed average UCS for the deep mixed elements was 150 psi. Requirements for the retaining wall were to resist static loads and to limit permanent lateral deformations to about 6 inches during an earthquake with an exceedance probability of 20% in 50 years (PGA = 0.47g). At more critical locations, such as adjacent to the Taxiway B bridge abutments, the wall was designed for permanent lateral deformations of about 4 inches during an earthquake with an exceedance probability of 5% in 50 years (PGA = 0.70g). To ensure good drainage, geocomposite drain strips, collector pipes, and a DMM cutoff wall were incorporated into the design. Because of limited working space and the operation of the existing airport, only one set of equipment was allowed for construction. DMM operations were completed using a specially made batch plant and a soil mixing rig with a triple-axis mixing tool.<br><h2>Complementary Technologies Used:</h2>Soil nailing for reinforcement</p><p><figure id='attachment_3414' style='max-width:594px' class='caption aligncenter'><img class="wp-image-3414 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Plan view layout of the DMM columns used to make the wall." width="594" height="379" /><figcaption class='caption-text'> Geometric design for DMM block treatment (From Yang 2003).</figcaption></figure></p><p><figure id='attachment_3415' style='max-width:657px' class='caption aligncenter'><img class="wp-image-3415 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematic diagram of a DMM gravity wall showing soil nailing used to develop grade separation structure." width="657" height="515" /><figcaption class='caption-text'> Design of DMM Gravity Wall (From Yang 2003).</figcaption></figure><h2>Performance Monitoring:</h2>The batch plant was equipped with scales and monitors to ensure proper proportioning of grout mix. The soil mixing rig was equipped with sensors to ensure verticality of soil-cement columns and to monitor depth, penetration and withdrawal rates, rotation speed, and grout injection rate. Data from the monitors was displayed on a computer screen for real time control of the DMM operation. To<br>ensure that the installed elements met project requirements, one full-depth core sample was taken per 500 linear feet of single-row DMM wall. One sample from every two core runs was subjected to UCS testing.<br><h2>Project Technical Paper:</h2>Rutherford, C., Biscontin, G., and Briaud, J-L. (2004). <em>Design Manual for Excavation Support Using Deep Mixing Technology</em>, Texas A&amp;M University, College Station, TX. 276p.</p><p>Yang, D.S. (2003). “Soil-cement walls for excavation support.” Earth Retention Systems 2003: A Joint Conference. ASCE Metropolitan Section Geotechnical Group, The Deep Foundations Institute, and ADSC: The International Association of Foundation Drilling; New York City, 6-7 May, pp. 1-17.</p><p>Yang, D.S., Scheibel, L.L., Lobedan, F. and Nagata, C. (2001). “Oakland Airport Roadway Project,” Soil Mixing Specialty Seminar, 26th DFI Annual Conference, St. Louis, MO, pp. 55–71.<br><h2>Date Case History Prepared:</h2>December 2014</p></p>