<p><p><h2>Preferred QC/QA Procedures</h2>The Federal Highway Administration (FHWA) does not currently have an accepted QC/QA document for the Vibro-Concrete Column (VCC) technology. Recommended QC/QA guidelines and summaries of individual methods are provided below.</p><p>Construction quality is achieved by meeting established requirements, as detailed in project plans and specifications, including applicable codes and standards. Quality Control (QC) and Quality Assurance (QA) are terms applied to the procedures, measurements, and observations used to ensure that construction satisfies the requirements in the project plans and specifications. QC and QA are often misunderstood and used interchangeably. Herein, Quality Control refers to procedures, measurements, and observations used by the contractor to monitor and control the construction quality such that all applicable requirements are satisfied. Quality Assurance refers to measurements and observations by the owner or the owner's engineer to provide assurance to the owner that the facility has been constructed in accordance with the plans and specifications.</p><p>The components of QC/QA monitoring programs for VCC technology are listed in Tables 1, 2, and 3. The entries in the tables are a list of typical items, not a list of all methods that could be used for QC/QA. Some QC procedures and measurement items may also serve as QA procedures and measurement items.<br><h3>TABLE 1. TYPICAL EXISTING QC/QA PROCEDURES & MEASUREMENT ITEMS</h3><table class='tablepress' id='tablepress-2062'><thead><th><center>QC or QA</th><th><center>Material or Process</th><th><center>Items</th></thead><tbody><tr><td ><center>QC</td><td ><center>Material Related</td><td >•Verify rebar certification
•Concrete mix design
</td></tr><tr><td ><center>QC</td><td ><center>Process Control</td><td >•Column diameter
•Column length
•Column spacing, as-built location
•Continuity/integrity of column
•Verticality of column
•Monitoring of installation parameters
</td></tr><tr><td ><center>QA</td><td ><center>Material Related</td><td >•Verify rebar certification
•Concrete mix design
</td></tr><tr><td ><center>QA</td><td ><center>Process Control</td><td >•Column diameter
•Column length
•Column spacing, as-built location
•Continuity/integrity of column
•Verticality of column
•Monitoring of installation parameters
</td></tr></tbody></table><br><h3>Table 2. PERFORMANCE CRITERIA USE IN QC/QA MONITORING PROGRAMS</h3><table class='tablepress' id='tablepress-2063'><thead><th><center>Topics</th><th><center>Items</th></thead><tbody><tr><td ><center>Material Parameters</td><td >•Concrete cylinder strength</td></tr><tr><td ><center>System Behavior</td><td >•Column capacity and predicted settlements
•Lateral deformation under load
</td></tr></tbody></table><br><h3>Table 3. EMERGING QC/QA PROCEDURES AND MEASUREMENT ITEMS</h3><table class='tablepress' id='tablepress-2064'><thead><th><center>Topics</th><th><center>Items</th></thead><tbody><tr><td ><center>Material Related</td><td >•None noted</td></tr><tr><td ><center>Process Control</td><td >•Automated monitoring of installation parameters
•Verify column dimensions through sonic integrity testing
</td></tr></tbody></table></p></p>
<p><p><h2>QC/QA Guidelines</h2>The limited specific design information for VCCs may be overcome by thorough QC/QA testing. With an adequate combination of load testing, material verification, geometry verification of each individual column, and sonic integrity testing, VCCs have been reliable embankment support elements for over a decade. In most cases, a combination of automated and manual record keeping is ideal. The comprehensive QC/QA program should be developed on a case‑by‑case basis and may or may not be governed by local codes.</p><p>QC consists of conducting load tests on test columns, verifying material properties, and monitoring construction to verify individual column geometry. Load tests are typically required to determine the capacity and settlement of the column. Load tests should be conducted in general accordance with ASTM D-1143, <em>Standard Test Methods for Deep Foundations Under Static Axial Compressive Load</em>, except that the Design Load (DL) of the VCCs is at least 1.5 times the required service load. Test should be conducted on individual columns after all excess pore pressures induced by construction have dissipated and the concrete has hardened to sufficient compressive strength. Material properties should be verified by obtaining rebar certifications and testing sample concrete cylinders in accordance with ASTM C1077, <em>Standard Practice for Agencies Testing Concrete and Concrete Aggregates for Use in Construction and Criteria for Testing Agency Evaluation</em>. Seven test cylinders shall be made from every 50 cubic yards of material or each daily batch, whichever is less. One pair of cylinders shall be tested at an age of 7 days, three cylinders at 28 days, and one pair shall be held in reserve for further testing, if required. Adjacent columns with 7.5-foot center-to-center spacing or less shall not be installed within 12 hours of each other. Column centers shall be located to an accuracy of ±4 inches of the plan location. Columns shall be plumb within 5%. The top elevation of the columns shall be within ±3 inches of the plan elevation (PSTS for VCC<a href="#_ftn1" name="_ftnref1">[1]</a>). Records should be kept for every column that include:<br><ul> <li>Column location or identification number.</li> <li>Column design load capacity.</li> <li>Ground surface and tip elevation.</li> <li>Time to penetrate and time to form each column.</li> <li>Amperage achieved with depth.</li> <li>Pumping pressure and volume with depth.</li> <li>Column diameter with depth and top diameter.</li> <li>Concrete mixture and amount of any additional water that may be added.</li> <li>Details of obstructions, delays and any unusual ground conditions.</li> <li>Digital data log of amperage, pressure, volume of concrete, and depth.</li></ul>QA should consist of load tests and may include sonic integrity testing to verify column capacity and integrity. At least one VCC load test shall be performed per structure/embankment. All load tests shall be performed prior to production work (PSTS for VCC).</p><p>Two specifications are available with limited QC/QA data, <em>Project Specific Technical Specification for Vibro Concrete Columns</em> and <em>Vibro-Concrete Column Construction Notes</em>.</p><p><a href="#_ftnref1" name="_ftn1"></a></p><p><hr /></p><p><a href="#_ftnref1" name="_ftn1">[1]</a> <em>Project Specific Technical Specification for Vibro-Concrete Columns</em></p></p>
<p><p><h2>References</h2>Elias, V., Welsh, J., Warren, J., Lukas, R., Collin, J.G., and Berg, R.B. (2006). “Ground improvement methods-Volume I.” Federal Highway Administration, FHWA NHI-06-019.</p><p>Hussin, J.D. (1994). “Ground modification with vibro concrete columns.” ASCE South Florida Section Meeting, Sept 30 – Oct 1, Ft Lauderdale, FL, 6 p.</p><p>ISSMGE, TC-17 Working Group D. “Application of ground improvement: vibro-replacement.” <<a href="http://www.bbri.be/homepage/download.cfm?dtype=services&doc=WGD_4_v…; (10 April 2009).</p><p>Mankbadi, R., Mansfield, J., Wilson-Fahmy, R., Hanna, S., and Krstic, V. (2004). “Ground improvement utilizing vibro-concrete columns.” <em>GeoSupport 2004</em>. 1-12.</p><p>Mankbadi, R., Mansfield, J., and Ramakrishna, A. (2008). “Performance of geogrid load transfer platform over vibro-concrete columns.” <em>GeoCongress 2008</em>. 748-756. <a href="http://ascelibrary.org/doi/abs/10.1061/40713%282004%2955">http://asceli…, V.R. (editor) (1997) “Ground improvement, ground reinforcement, ground treatment, developments, 1987 1997” Geotechnical<em> Special Publication No. 69: Proceedings of the sessions sponsored by the Committee on Soil Improvement and Geosynthetics of the Geo-Institute of the American Society of Civil Engineers in conjunction with Geo-Logan ’97</em>. Logan, Utah, July 17-19, 1997.</p><p>Schaefer, V.R., Berg, R.R., Collin, J.G., Christopher, B.R., DiMaggio, J.A., Filz, G.M., Bruce, D.A., and Ayala, D. (2016). “Ground Modification Methods,” Federal Highway Administration, Washington, DC, FHWA NHI-16-027 (Vol. I), 386p. <a href="https://www.fhwa.dot.gov/engineering/geotech/pubs/nhi16027.pdf">https:/…, C.J., and Synac, O. (2007). “Ground improvement solutions for motorway widening schemes and new highway embankment construction over soft ground.” <em>Ground Improvement</em>. Vol 11, No 4, 219-228.</p></p>