<p><p><h2>Preferred QC/QA Procedures</h2>Blast densification has no recommended FHWA quality control or quality assurance procedures. Several methods are commonly employed in practice including Cone Penetration Tests (CPT), settlement measurements, vibration monitoring, porewater pressure monitoring, Standard Penetration Tests (SPT), and shear wave velocity (V<sub>s</sub>) measurement. It is recommended that a combination of these methods be applied for QC/QA.</p><p>Most blast densification programs are used for improvement of cohesionless soils and employ CPT and SPT tests to determine whether adequate improvement has been obtained. Settlement monitoring provides a preliminary estimate of the success of the blasting, but correlations between settlement and densification within the specific strata and zones to be improved may be difficult to develop and may produce uncertain results. Shear wave velocity measurements can be performed in conjunction with borings or CPTs and provide information about the level of improvement. Vibration monitoring is usually required during the blasting program to assure that dynamic effects are within acceptable limits. Pore pressure measurement can be used to ensure that blast-induced pore pressures:<br><ol> <li>Are sufficient to breakdown the initial soil structure.</li> <li>Dissipate before subsequent blast coverages.</li></ol>For projects requiring the improvement of large areas, it is desirable to subdivide the total area into approval or acceptance zones on the order of 100 feet on a side. Completing the work with timely approval on a zone-by-zone basis means that the contractor may proceed without risk of having to return late in the project to correct deficiencies that developed early in the project.</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 blast densification 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><strong>TABLE 1. TYPICAL EXISTING QC/QA PROCEDURES AND MEASUREMENT ITEMS</strong></h3><table class='tablepress' id='tablepress-1921'><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 >•Density of soil before and after densification using CPT, SPT, or shear wave velocity measurements</td></tr><tr><td ><center>QC</td><td ><center>Process Control</td><td >•Grid and depth layout of charges
•Vibration monitoring
•Porewater pressure monitoring
</td></tr><tr><td ><center>QA</td><td ><center>Material Related</td><td >•Density of soil before and after densification using CPT, SPT, or shear wave velocity measurements</td></tr><tr><td ><center>QA</td><td ><center>Process Control</td><td >•Spacing of charges
•Porewater pressure monitoring
•Vibration monitoring
</td></tr></tbody></table><br><h3><strong>TABLE 2. PERFORMANCE CRITERIA USE IN QC/QA MONITORING PROGRAMS </strong></h3><table class='tablepress' id='tablepress-1922'><thead><th><center>Topics</th><th><center>Items</th></thead><tbody><tr><td ><center>Material Parameters</td><td >•Settlement plates
•Density of soil using CPT, SPT, or shear wave velocity measurements
</td></tr><tr><td ><center>System Behavior</td><td >•Amount of overall settlement after blasting
•Density measurements before and after blasting
</td></tr></tbody></table><br><h3><strong>TABLE 3. EMERGING QC/QA PROCEDURES AND MEASUREMENT ITEMS</strong></h3><table class='tablepress' id='tablepress-1923'><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 settlement measurements</td></tr></tbody></table></p><p> </p></p>
<p><p><h2>QC/QA Guidelines</h2>QC/QA programs should take into account:<br><ol> <li>Spacing between CPT or SPT tests (testing frequency). At least one CPT profile approximately every 2000 m<sup>2</sup></li> <li>Location of tests relative to blast-hole locations.Usually, penetration or other in-situ tests should be located at the centroid of the area defined by the blast-hole pattern; i.e., at the greatest distance from the charges.</li> <li>Minimum time between the end of blasting and verification testing.Tests have shown that improvement in penetration resistance may continue over periods from several days to years after the blasting is completed.</li> <li>Minimum values of penetration resistance or other measured property at a specified time (usually about one or two weeks following the completion of blasting). The specific values in any case are usually determined from the results of site‑specific field trials. Some guidance is given by the following:<br><ol style="list-style-type: lower-alpha;"> <li>For initial relative densities of 30 to 50%, volume changes of 4 to 10% and final relative densities of 65 to 80% are common (Gohl et al. 2000)</li> <li>An increase in relative density of 15 to 30% can be achieved (Mitchell 1970)</li></ol></li> <li>Minimum percentage of failing tests, the lowest acceptable values, and their distribution throughout the site</li> <li>Maximum vibration velocities at different locations. Based on Bureau of Mines tests, maximum velocities should be limited to:<br><ol style="list-style-type: lower-alpha;"> <li>50 mm/sec to avoid cosmetic damage in most modern buildings.</li> <li>25 in./sec (6.4 mm/sec) for historic buildings.</li></ol></li> <li>Minimum acceptable level of pore pressure generation</li></ol>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>Ashford, S.A., Rollins, K.M., and Lane, J.D. (2004). “Blast-induced Liquefaction for Full-Scale Foundation Testing.” Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 130(8), pp. 798-806.</p><p>Fordham, C.J., McRoberts, E.C., Purcell, B., and McLaughlin, P. (1991). “Practical and theoretical problems associated with blast densification of loose sands.” <em>Canadian Geotechnical Conference Proceedings</em>. pp. 941-948.</p><p>Gandhi, S.R., Dey, A.K., and Selvam, S. (1999). “Densification of pond ash by blasting.” <em>Journal of Geotechnical and Geoenvironmental Engineering</em>, ASCE, 125(10). pp. 889-899.</p><p>Gohl, W.B., Jefferies, M.G., Howie, J.A., and Diggle, D. (2000). “Explosive compaction: design, implementation and effectiveness.” <em>Géotechnique</em>, 50(6), pp. 657-665.</p><p>Mitchell, J.K. (1970). “In-Place Treatment of Foundation Soils.” ASCE <em>Journal of the Soil Mechanics and Foundations Division, </em>Vol. 96, No. 1, pp. 73-110.</p><p>Narin van Court, W.A. and Mitchell, J.D. (1994a). <em>Explosive Compaction: Densification of Loose, Saturated, Cohesionless Soils by Blasting, </em>Geotechnical Engineering Report No. UCB/GT/94-03, Department of Civil Engineering, University of California-Berkeley.</p><p>Narin van Court, W.A. and Mitchell, J.K. (1994b). “Soil improvement by blasting: part I.” <em>Journal of Explosives Engineering</em>, Vol. 12, No. 3, pp. 34-41, Nov./Dec.</p><p>Narin van Court, W.A. and Mitchell, J.K. (1995a). “Soil improvement by blasting: part II.” <em>Journal of Explosives Engineering</em>, Vol. 12, No. 4, pp. 26-34, Jan./Feb.</p><p>Narin van Court, W.A. and Mitchell, J.K. (1995b). "New Insights into Explosive Compaction of Loose, Saturated, Cohesionless Soils." <em>Soil Improvement for Earthquake Hazard Mitigation</em>, ASCE Geotechnical Special Publication No. 49, pp. 51-65.</p><p>Narsilio, G.A., Santamarina, J.C., Hebeler, T.,and Bachus, R. (2009). “Blast Desification: Multi-Instrumented Case History.” <em>Journal of Geotechnical and Geoenvironmental Engineering</em>, 135(6) 723-734.</p><p>Solymar, Z.V. (1984). “Compaction of alluvial sands by deep blasting.” <em>Canadian Geotechnical Journal</em>, 21, 305-321.</p><p> </p></p>