<p><p><figure id='attachment_1866' style='max-width:600px' class='caption aligncenter'><img class="wp-image-1866" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematic illustration of dynamic compaction. Diagram shows a crane dropping a weight into the ground with waves emanating from the resulting depression." width="600" height="561" /><figcaption class='caption-text'> Schematic illustration of dynamic compaction (Elias et al. 2006).</figcaption></figure><h2>Basic Function:</h2>Deep Dynamic Compaction (DDC) densifies marginal materials using high levels of impact energy at the surface.<br><h2>Advantages:<em> </em></h2><ul> <li>Suitable for many types of soils with less than 15% fines</li> <li>Low cost for large area of improvement</li> <li>Ability to measure improvement</li> <li>Many available contractors</li> <li>Simple equipment</li> <li>Produces relatively uniform compressibility</li></ul><h2>General Description:</h2>DDC applies energy by raising and dropping a tamper (weight) repeatedly from a height of 30 to 120 feet. The energy densifies the soil to depths that increase with the magnitude of the energy. The ground surface is then compacted with a smaller, broader tamper or conventional compaction equipment.<br><h2>Geologic Applicability:</h2><ul> <li>Loose pervious and semi-pervious soils with fines contents less than 15%</li> <li>Materials containing large voids</li> <li>Soil improvement to a maximum depth of about 30 to 35 feet</li> <li>Not recommended for silty or clayey soils</li> <li>Effective in soils above or below the groundwater table (Note: Water table should be 6 feet below grade; fill can be placed above a high groundwater site to achieve this distance.)</li></ul><h2>Construction Methods:</h2>A tamper with a weight of 5 to 40 tons is dropped using a crane from a height of 30 to 120 feet. The tamper is dropped in a systematically controlled pattern on a coordinate grid layout. The impacts are spaced at a distance depending on the depth of the compressible layer, the depth to the groundwater, and grain size distribution. Five to 15 blows per grid point are applied. The first phase is the high-energy phase to improve the deeper layers. This is followed by a low-energy phase to densify the upper layers. In the low-energy phase, the tamper is only raised 15 to 20 feet. Backfilling the craters and additional passes may be required.<br><h2>Additional Information:</h2>Proximity of groundwater or excessive crater depths limit the number of blows at each grid point. In saturated soils with some fines (less than 15% fines), the compaction may create excess pore water pressure that reduces the effectiveness of compaction unless the pressure is dissipated. DDC is more economical than other technologies for large area ground improvements.<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>Densification of Loose Pockets &amp; Voids – FL</li> <li>Study Site – Charleston, SC</li></ul><h2>Complementary Technologies:</h2>Prefabricated vertical drains (without fill preloading) to dissipate pore water pressures and permit densification of soils with higher fines content.<br><h2>Alternate Technologies:</h2>Excavation and replacement, sand compaction columns, vibrocompaction, blasting densification, aggregate columns, and deep foundation systems.<br><h2>Potential Disadvantages:</h2><ul> <li>Mobilization costs</li> <li>Large ground vibrations and lateral displacements</li> <li>Limited effective treatment depth</li> <li>Some safety concerns</li></ul><h2>Key References for this technology:</h2>Elias, V., Welsh, J., Warren, J., Lukas, R., Collin, J. G., and Berg, R. R. (2006). “Ground Improvement Methods”- Volume I. Federal Highway Administration Publication No. NHI-06-020.</p><p>Lukas, R.G. (1986). “Dynamic Compaction for Highway Construction Volume I: Design and Construction Guidelines.” U.S. Department of Transportation, Federal Highway Admin., Washington, D.C., FHWA/RD-86/133.</p><p>Lukas, R.G. (1995). “Dynamic Compaction – Geotechnical Engineering Circular No. 1”, U.S. Department of Transportation, Federal Highway Administration, Washington, D.C., FHWA-SA-95-037.</p></p>