<p><p><h2>Preferred QC/QA Discussion</h2>No FHWA document exists which is considered to provide a comprehensive and thorough description of implementing a QC/QA program for vibrocompaction. A typical testing program depends on the primary design goal of the vibrocompaction project; e.g. bearing capacity increase, settlement reduction, or liquefaction prevention. Based on the design goal, the QC/QA process will place higher emphasis on different testing methods.</p><p>For projects where a higher bearing capacity is desired, data logger records, surface settlement markers, and Cone Penetration Tests (CPTs) and/or Standard Penetration Tests (SPTs) should be performed. For projects where an increase in liquefaction resistance is the primary goal, shear wave velocity testing, data logger records, and CPT and/or SPTs should be performed. Projects, which utilize backfill for each vibrocompaction point, must include particle size distribution tests to confirm the specified backfill material is being used. A more aggressive QC/QA program might require plate load testing. However, this method is only able to provide information about the improvement of a shallow depth.</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 vibrocompaction are listed in Tables 1, 2, and 3<em>.</em> 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-2059'><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 >•Backfill gradation
•Relative density before and after densification (from CPT, SPT, or shear wave velocity)
•Plate load test results
</td></tr><tr><td ><center>QC</td><td ><center>Process Control</td><td >•Data logger records
•Grid layout and spacing
</td></tr><tr><td ><center>QA</td><td ><center>Material Related</td><td >•Backfill gradation
•Relative density before and after densification (from CPT, SPT, or shear wave velocity)
•Plate load test results
</td></tr><tr><td ><center>QA</td><td ><center>Process Control</td><td >•Surface settlement during construction
•Grid layout and spacing
</td></tr></tbody></table><br><h3>Table 2. PERFORMANCE CRITERIA USE IN QC/QA MONITORING PROGRAMS</h3><table class='tablepress' id='tablepress-2060'><thead><th><center>Topics</th><th><center>Items</th></thead><tbody><tr><td ><center>Material Parameters</td><td >•Relative density
•SPT N-value
•CPT penetration resistance
•Shear wave velocity
</td></tr><tr><td ><center>System Behavior</td><td >•Post-construction surface settlement and 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-2061'><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 >•None noted</td></tr></tbody></table></p></p>
<p><p><h2>QC/QA Guidelines</h2>Data logger records should be maintained for every vibrocompaction point to assure a uniform compactive effort with depth and that consistent implementation methods are followed. These records will also provide evidence of adherence to specifications. According to the FHWA Ground Modification reference manual (Schaefer et al., 2016), the following information should be recorded:<br><ul> <li>Verification that probe penetration depth is acceptable</li> <li>Verification that probe withdrawal rate is acceptable</li> <li>Monitoring the probe penetration rate to obtain a rough indication of the type and density of soil penetrated</li> <li>Verification that compaction points are at the proper locations</li> <li>Monitoring the volume of backfill added to obtain an indication of the densities achieved</li> <li>Verification that backfill gradation is acceptable</li> <li>Monitoring of ammeter or hydraulic pressure readings to verify that the build-up is sufficient</li> <li>Verification that the probes are operating at appropriate speeds</li> <li>Verification that induced vibrations are not excessive when operating close to existing structures (maximum particle velocity measurements)</li></ul>The adequacy of compaction and construction methods can be verified through CPTs, SPTs, and/or plate load tests. The same test method should be utilized before and after construction in order to determine the amount of soil strength improvement; i.e. designs based on CPT values should utilize CPT tests during quality assurance.</p><p>Shear wave testing can be completed through cross-hole tests or the spectral analysis of surface wave method. The shear wave velocity can be used to determine the site’s ability to resist liquefaction using methods proposed in Andrus and Stokoe (2000).</p><p>Schaefer et al. (2016) describes how surface settlement markers provide a method to find an average increase in relative density and compaction. Surface settlement markers cannot be used to check for minimum compaction achieved. It should be noted that during vibrocompaction, the soil near the surface will be significantly less compacted than the rest of the improved layer. Some sort of surface compaction program will need to be implemented after the completion of the vibrocompaction project. If a significant amount of settlement has occurred due to vibrocompaction, a fill layer may need to be placed to bring the site up to grade.</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 <em>Individual QC/QA Methods </em>section below.</p></p>
<p><p><h2>References</h2>Andrus, R.D. and Stokoe II, K.H. (2000). “Liquefaction resistance of soils from shear-wave velocity” <em>J Geotech Geoenviron Eng</em> <strong>126</strong> (2000) (11), pp. 1015–1025.</p><p>Massarsch and Fellenius (2001). “Vibratory compaction of coarse-grained soils.” Canadian Geotechnical Journal, vol. 39, No. 3, 25p.</p><p>Massarsch, K.R. and Fellenius, B.H. (2005). “Deep vibratory compaction of granular soils.” Chapter 19 in <em>Ground Improvement – Case Histories</em>, Elsevier publishers, B. Indranatna and J. Chu (Editors), 633-658.</p><p>Massarsch, K.R. and Heppel, G. (1991). “Deep Vibratory Compaction using the Muller Resonance Compaction (MRC) System.” Report 91:2, Muller Geosystems.</p><p>Mitchell (1981). “Soil Improvement: State of the Art Report.” <em>Proceedings of the Tenth ICSMFE, </em>Stockholm, Sweden, Vol. 4, pp. 509-565.</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.</p><p><a href="https://www.fhwa.dot.gov/engineering/geotech/pubs/nhi16027.pdf">https:/…, J., <a href="http://adsabs.harvard.edu/cgi-bin/author_form?author=Stokoe,+K&full…, K. H.</a>, <a href="http://adsabs.harvard.edu/cgi-bin/author_form?author=Roesset,+J&ful…, J. M.</a>, and <a href="http://adsabs.harvard.edu/cgi-bin/author_form?author=Hudson,+W&full…, W. R.</a> (1986) "Applications and Limitations of the Spectral-Analysis-of-Surface-Waves Method." Final Research Report Texas Univ., Austin. Center for Transportation Research. (Nov. 1986).</p></p>