<p><p><h2> Preferred QC/QA Procedures</h2><strong>Summary</strong></p><p>Construction quality is achieved by meeting established requirements, as detailed in project plans and specifications, including applicable test standards by ASTM and AASHTO, for example. 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, QC refers to procedures, measurements, and observations used by the contractor to monitor and control the construction quality such that all applicable requirements are satisfied. QA 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 FHWA <em>Design Manual for Deep Mixing for Embankment and Foundation Support</em> (Bruce et al. 2013) addresses preferred QC/QA procedures for Deep Mixing Methods. At a minimum, the QC/QA program should consist of laboratory mix trials (bench scale testing), installation monitoring, and some form of post-construction verification method. In addition, pre-production field validation testing is performed on most projects. In this document, various test procedures and guidelines are summarized and the QC/QA parameters to be measured are provided.</p><p>The laboratory mix trials provide an index of the field properties and help determine or confirm the binder selection. Installation monitoring is an essential quality control process that provides an indication of the mixing energy applied, the binder factor achieved, and the geometry of the improved soil. Typically, each column is monitored, thereby providing a high rate of coverage. It is recommended that the field monitoring reports be reviewed by the owner’s engineer for selection of columns to be tested as part of the quality assurance process. Post-construction verification methods are another essential process for quality assurance that provide the relationship between the index of mixture strength from laboratory tests and the actual properties of the improved soil in the field. In current U.S. practice, the most prevalent post-construction verification method is sampling and unconfined compressive strength testing. The samples are obtained by coring and wet grab sampling.</p><p>Installation monitoring combined with statistical analysis of sample strengths appear to be the most reliable way of ensuring that the required geometry, degree of mixing, and shear strength of the improved ground has been achieved.</p><p>Field validation testing (or installation of demonstration columns installed prior to constructing the production columns) is also a common and very useful part of the QC/QA program, as it allows the contractor to validate the effectiveness of binder type, binder quality, mixing equipment, and other parameters such as blade rotation, penetration, and withdrawal rates. The field validation testing can also confirm other components of the QC/QA program such as construction monitoring, core sampling, and wet grab sampling procedures.</p><p>Though not typically performed in the U.S., extraction or excavation of columns is a very useful technique that could be employed more often, when conditions permit.</p><p>The components of QC/QA monitoring programs for Deep Mixing Methods 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 AND MEASUREMENT ITEMS</h3><table class='tablepress' id='tablepress-1943'><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 >• Procedures: laboratory mix trials, unit weight of slurry, field test columns, wet grab sampling, strength testing, hydraulic conductivity testing
• Measure: strength, permeability
</td></tr><tr><td ><center>QC</td><td ><center>Process Control</td><td >• Procedures: installation monitoring, surveying
• Measure: blade rotation rate, penetration/ withdrawal rate, binder mix quantity, verticality, injection pressure, geometry of improved soil
</td></tr><tr><td ><center>QA</td><td ><center>Material Related</td><td >• Procedures: core sampling, wet grab sampling, penetration/pullout test, pressuremeter testing, extraction/excavation, geophysical testing
• Measure: degree of mixing/uniformity, strength, permeability
</td></tr><tr><td ><center>QA</td><td ><center>Process Control</td><td >• Procedures: core sampling, extraction/excavation, geophysical testing, surveying
• Measure: verticality, degree of mixing/uniformity, geometry of improved soil
</td></tr></tbody></table><br><h3>TABLE 2. PERFORMANCE CRITERIA USE IN QC/QA MONITORING PROGRAMS</h3><table class='tablepress' id='tablepress-1944'><thead><th><center>Topics</th><th><center>Items</th></thead><tbody><tr><td ><center>Material Parameters</td><td >• Shear strength, bearing capacity, stiffness/modulus, permeability
</td></tr><tr><td ><center>System Behavior</td><td >• Settlement, lateral deformation, structural failure of columns</td></tr></tbody></table><br><h3>TABLE 3. EMERGING QC/QA PROCEDURES AND MEASUREMENT ITEMS</h3><table class='tablepress' id='tablepress-1945'><thead><th><center>Topics</th><th><center>Items</th></thead><tbody><tr><td ><center>Material Related</td><td >• Additional applications of geophysics</td></tr><tr><td ><center>Process Control</td><td >• None noted</td></tr></tbody></table></p></p>
<p><p><h2>QC/QA Guidelines</h2>At a minimum, the QC/QA program should consist of laboratory mix trials, installation monitoring, and some form of post-construction verification method, preferably core sampling and/or wet grab sampling. Pre-production field trials are also employed on most deep mixing projects.</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></p></p>
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