<p><p><figure id='attachment_2637' style='max-width:740px' class='caption aligncenter'><img class="wp-image-2637 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematic diagram showing the mail elements of vibratory compaction equipment." width="740" height="520" /><figcaption class='caption-text'> Main elements of vibratory compaction equipment (after Massarch and Fellenius 2005)</figcaption></figure><h2>Basic Function:</h2>Vibrocompaction densifies deep cohesionless soils to increase bearing capacity, increase shear strength, reduce settlement, and increase liquefaction resistance.<br><h2>Advantages:<em> </em></h2><ul> <li>More economical and faster construction than deep foundations.</li> <li>Many case histories in United States.</li> <li>Effective above and below water table.</li></ul><h2>General Description:</h2>Vibrocompaction is a method of deep densification. It can be used on cohesionless soils through penetration and vibration of a probe to densify the surrounding soil.<br><h2>Geologic Applicability:</h2><ul> <li>Cohesionless soils.</li> <li>Applicable soils include clean sands with less than 15% silts and/or less than 2% clay.</li> <li>Typical depths range from 10 to 50 feet (3 to 15 meters).</li> <li>Range may be as low as 3 feet (1 meter) and as deep at 120 feet (37 meters).</li></ul><h2>Construction Methods:</h2>Vibrocompaction is performed using the penetration and vibration of a probe to rearrange soil particles into a denser state. The design includes the layout of triangular or rectangular grid points, the spacing of the grid points, and the depth of vibrocompaction. Typical spacing of grid points range from 5 to 15 feet (1.5 to 5 meters) depending on the soil type, the density of the soil, and the soil density goal. Typical depth of vibrocompaction ranges from 10 to 50 feet (3 to 15 meters). Sand can be backfilled into the craters to maximize the densification, but in many instances, is not. During insertion and extraction of the probe, the frequency of vibration should be greater than 30 Hz to decrease shaft resistance. During the compaction phase, the frequency is generally between 15 and 20 Hz. The probe should be inserted to the required depth as quickly as possible at a high frequency. Then, the soil is compacted at the resonance frequency, followed by removing the probe quickly at a high frequency. SPT and CPT results help determine the final density achieved, as well as strength, deformation, and liquefaction resistance. Design charts are available in the literature.<br><h2>Additional Information:</h2>Vibrocompaction can be more cost efficient than excavation and replacement and deep foundation systems. The compactibility of the soils at the site can be evaluated before vibrocompaction based on soil grain size analyses and the SPT and CPT resistances. Vibrocompaction can increase the angle of internal friction by 5 to 10 degrees.<br><h2>SHRP2 Applications:</h2><ul> <li>New Embankment and Roadway Construction</li> <li>Roadway and Embankment Widening</li></ul><h2> Example Successful Applications:</h2><ul> <li>Wando Terminal Port – Charleston, SC</li> <li>I-90 Mt. Baker Ridge – Seattle, WA</li> <li>Manchester Airport – NH</li></ul><h2>Complementary Technologies:</h2>Generally used alone. Prefabricated vertical drains can be used to speed up consolidation and drainage.<br><h2>Alternate Technologies:</h2>Sand compaction piles, deep dynamic compaction, aggregate columns, vibro-concrete columns<br><h2>Potential Disadvantages:</h2>Narrow range of soils that the method can improve. Noise and vibration. Contractor experience is critical. Quality control should be carefully monitored.<br><h2>Key References for this technology:</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, Publication No. FHWA NHI-06-019.</p><p>Massarsch, K.R. and Fellenius, B.H. (2001). “Vibratory compaction of coarse-grained soils.” <em>Canadian Geotechnical Journal</em>, 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>