<p><p><h2>Preferred QC/QA Procedures</h2>Geotextile Encased Columns (GECs) have no FHWA recommended quality control or quality assurance procedures, and little documentation is available on typical procedures. The procedures that are documented pertain to quality assurance and assessing the performance of the columns after construction. None of these procedures are proprietary. The literature discusses comparisons of soil strength before and after installation of the columns, but none of the papers explain the method used for determining these strengths. Standard QC/QA procedures and tests (e.g., wide-width strength) can be used to check the properties of the geotextile tube. The manufacturer of the geotextiles used for GECs could be consulted for additional QC/QA procedures relating to the geotextile.</p><p>Construction quality is achieved by meeting established requirements, as detailed in project plans and specifications, including any 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. 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 GECs are listed in Tables 1, 2, and 3. The entries in the table 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 AND MEASUREMENT ITEMS</h3><table class='tablepress' id='tablepress-1983'><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 >•Fill material property testing
•Density of surrounding soil before and after installation
•Shear strength of surrounding soil before and after installation
</td></tr><tr><td ><center>QC</td><td ><center>Process Control</td><td >•Monitoring of GEC placement locations and depth</td></tr><tr><td ><center>QA</td><td ><center>Material Related</td><td >•Density of surrounding soil before and after installation
•Penetration tests inside column
</td></tr><tr><td ><center>QA</td><td ><center>Process Control</td><td >•None noted</td></tr></tbody></table><br><h3>TABLE 2. PERFORMANCE CRITERIA USE IN QC/QA MONITORING PROGRAMS</h3><table class='tablepress' id='tablepress-1984'><thead><th><center>Topics</th><th><center>Items</th></thead><tbody><tr><td ><center>Material Parameters</td><td >•Static load tests
•Settlement plates
</td></tr><tr><td ><center>System Behavior</td><td >•Load capacity
•Site settlement
</td></tr></tbody></table><br><h3>TABLE 3. EMERGING QC/QA PROCEDURES AND MEASUREMENT ITEMS</h3><table class='tablepress' id='tablepress-1985'><thead><th><center>Topics</th><th><center>Items</th></thead><tbody><tr><td ><center>Material Related</td><td >•Advanced GEC layout and geometry measurements</td></tr><tr><td ><center>Process Control</td><td >•GPS
•Inclinometers
•Automated settlement measurements
</td></tr></tbody></table></p></p>
<p><p><h2>QC/QA Guidelines</h2>During construction, the location and depth of installation for each column should be recorded using either manual or automated methods. Once installation of the columns is complete, the quality of the compacted soil within a column can be assessed with cone penetration tests within the column. The increase in shear strength in soil should be measured with the same method used to determine the shear strength prior to the installation of the columns. The performance of individual columns can be assessed with load tests.</p><p>The references reviewed do not provide QC/QA information on control of the GEC materials (i.e., the soil in-fill and the geotextile tube). Standard QC/QA procedures and tests (e.g., gradation) can be used to check the properties of the in-fill soil. Standard QC/QA procedures and tests (e.g., wide-width strength) can be used to check the properties of the geotextile tube. The manufacturer of the geotextiles used for the GECs could be consulted for additional information on QC/QA procedures relating to the geotextile tube, especially relating to preventing installation damage.</p><p>Inspections, construction observations, daily logs, and record keeping are essential QC/QA activities for all technologies. These activities help to ensure and/or verify that:<br><ul> <li>Good construction practices and the project specifications are followed.</li> <li>Problems can be anticipated before they occur, in some cases.</li> <li>Problems that do arise are caught early, and their cause can oftentimes be identified.</li> <li>All parties are in good communication.</li> <li>The project stays on schedule.</li></ul>Additional technology-specific details for inspections, construction observations, daily logs, and record keeping QC/QA activities are provided in the following <em>Individual QC/QA Methods </em>sections.</p></p>
<p><p><h2>References</h2>Brokemper, D., Sobolewski, J., Alexiew, D., and Brok, C. (2006). “Design and construction of geotextile encased columns supporting geogrid reinforced landscape embankments; Bastions Vijfwal Houten in the Netherlands.” <em>Geosynthetics</em>. Kuwano, J., and Koseki, J. editors. Millpress, Rotterdam.</p><p>Diehl, A. (2002). “Geotextile-Encased Columns® Möbius foundation system: an economical foundation system for embankments on soft subsoils.” Josef Möbius Bau-Aktiengesellschaft. Brochure No. 45-2002, 2002.</p><p>Mauer, A. (2001). “Enclosure and Heightening of the Airbus Works Extension ‘Mühlenberger Loch’.” Translator: R. Bütikofer. Josef Möbius Bau-Aktiengesellschaft. Brochure No. 40-2001, 2001.</p><p>Raithel, M., Kirchner, A., Schade, C., and Leusink, E. (2005). “Foundation of constructions on very soft soils with geotextile encased columns- State of the art.” Geotechnical special publication- Innovations in grouting and soil improvement, 136, 1867-1877.</p></p>