<p><p>&nbsp;</p><p><figure id='attachment_2566' style='max-width:1046px' class='caption alignnone'><img class="wp-image-2566 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Two photographs. Continuous flight auger pile rig to the left. Low Headroom Continuous flight auger Pile Application to the right." width="1046" height="578" /><figcaption class='caption-text'> CFA pile rig (left), Low Headroom CFA Pile Application (right). From Brown et al. (2007).</figcaption></figure><h2>Basic Function:</h2>Continuous Flight Auger piles (CFA) or Auger Cast-In-Place piles (ACIP) are a deep-foundation system to support loads.<br><h2>Advantages:<em> </em></h2><ul> <li>Rapid installation.</li> <li>Limited installation noise and vibration.</li> <li>Real time quality control.</li> <li>May be effective in limited headroom conditions.</li> <li>Low mobilization cost</li></ul><h2>General Description:</h2>Pre-blended sand cement columns are installed into the ground using a rotary bored displacement technique. Soil is improved both by densification and load transfer mechanisms. CFA piles can be used for the support of bridges, bridge widening, sound wall foundations, columns support of embankments, and secant walls for lateral earth support.<br><h2>Geologic Applicability:</h2><ul> <li>Medium to very stiff clay, cemented sand or weak limestone.</li> <li>Silty or clayey residual soils, with little cohesion.</li> <li>Medium dense to dense silty sands and well-graded sands.</li> <li>Stiff or cemented deposits overlying rock.</li> <li>Groundwater should be very deep.</li></ul><h2>Construction Methods:</h2>In constructing the CFA, a hollow-stem auger is drilled into the ground to form the pile diameter. Sand-cement grout or concrete is pumped into the hole as the auger is removed to create a cast-in-place column. A steel bar reinforcement cage can be inserted into the column if required. The diameter of the column is generally 12 to 36 inches (0.3 to 0.9 meters). The depth can range from 60 to 70 feet (18.2 to 21.3 meters). Other techniques can displace the soil laterally using auger tools.<br><h2>Additional Information:</h2>CFAs can support lateral earth loads for critical and noncritical structures. Presence of a high groundwater table can lead to soil mining or necking in some soils. Reported production rates reached 1,500 feet per day per rig. Cost data is limited but prices are reported to be $12/lf or $20/lf for 12- to 18‑inch diameter piles. Prices reached up to $60/lf to $80/lf for 30- to 36‑inch piles.<br><h2>SHRP2 Applications:</h2><ul> <li>New Embankment and Roadway Construction over Unstable Soils</li> <li>Roadway and Embankment Widening</li></ul><h2> Example Successful Applications:</h2><ul> <li>52 Story Apartment Building - New York City</li> <li>FedEx MidAtlantic Hub - Greensboro, North Carolina</li></ul><h2>Complementary Technologies:</h2>Column supported embankments with or without a load transfer mat.<br><h2>Alternate Technologies:</h2>Driven piles and drilled shafts. Micropiles when reinforcement of the pile is needed. Stone columns, rammed aggregate piers, and vibro-concrete columns when reinforcement is not needed.<br><h2>Potential Disadvantages:</h2><ul> <li>Difficult to maintain proper rate of penetration.</li> <li>Not suited for soils with rocks and boulders.</li> <li>Relatively new technology.</li> <li>Procedures have not been fully developed.</li> <li>Problematic in soft soils, loose sands, clean uniformly graded sands under groundwater, voids, pockets of water, hard soil, or rock overlain by loose soil.</li></ul><h2>Key Reference for this technology:</h2>Brown, D.A., Dapp, S.D., Thompson, W.R. and Lazarte, C.A. (2007). “Design and construction of continuous flight auger piles.” <em>Geotechnical Engineering Circular (GEC) No. 8</em>, U.S. Department of Transportation, Federal Highway Administration, Washington, D.C., 270 p.</p></p>