<p><p><figure id='attachment_2640' style='max-width:694px' class='caption aligncenter'><img class="wp-image-2640 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Diagrams of plan and profile layout of explosive charges for densification of loose sands." width="694" height="416" /><figcaption class='caption-text'> Mitchell, J.K. (1981). “Soil Improvement-State of the art report”. Proceedings of 10th ICSMFE. Stockholm, Vol. 4, pp 509-565.</figcaption></figure><h2>Basic Function:</h2>Blast densification (explosive compaction) densifies loose, relatively clean, cohesionless soils by liquefying the soil and consolidating.<br><h2>Advantages<strong>:</strong><em> </em></h2><ul> <li>Ability to treat deep soils</li> <li>Rapid technique</li> <li>Inexpensive</li> <li>Successful under a variety of climate and environmental extremes</li></ul><h2>General Description:</h2>Detonation of explosives induces liquefaction of the soils, which consolidate to a denser, more stable configuration due to the vibrations and force from the blast and gravity. Blast densification reduces effects of long-term settlement and improves the foundation soil strength.<br><h2>Geologic Applicability:</h2><ul> <li>Best suited for clean sand and silty sands with relative densities less than 50% to 60%, and with maximum clay content of 5 to 10%</li> <li>Has been used to treat soils up to depths of 130 feet</li> <li>Maximum effective depth has not been defined</li> <li>Has been used on saturated alluvial deposits, hydraulic fills, and volcanic debris flows</li></ul><h2>Construction Methods:</h2>Charges are placed in pre-drilled or jetted holes that are located in a grid pattern with charge spacings typically between 10 and 50 feet (3 to 15 meters). Several charges are fired at once, with delays between charges to enhance cyclic loading while minimizing peak acceleration. Often multiple passes of charges are required to reach the desired densification. The vertical spacing of the charges varies with the size of the charges and thickness of the layer to be densified. The size of the charge is based on empirical design equations, the single-pass grid spacing, and vibration constraints. Denser soils require larger charges to break down the soil structure.<br><h2>Additional Information:</h2>Volume reductions of 4 to 10% and relative density increases from 10 to 40% have been measured. Blast densification helps achieve long-lived projects by increasing foundation soil stability and strength and reducing the settlement over an extended period of time. The cost of the technology is relatively inexpensive compared to other technologies. This technology has not been widely used to date, but it is a proven technology that can provide rapid and cost effective construction.<br><h2>SHRP2 Applications:</h2>New Embankment and Roadway Construction<br><h2>Example Successful Applications:</h2><ul> <li>National Geotechnical Experimentation Site – Treasure Island, San Francisco, CA</li> <li>Blast Densification Field Study – South Carolina</li> <li>Highway 504 Bridge over Coldwater Creek – Mt. St. Helen’s, WA</li></ul><h2>Complementary Technologies:</h2>Blast technology is often used as a stand-alone method. It can be used to treat the deep soils while another technology is used for the surface soil.<br><h2>Alternate Technologies:</h2>Deep dynamic compaction, vibrocompaction, or other mechanical ground improvement techniques.<br><h2>Potential Disadvantages:</h2><ul> <li>Lack of validated theoretical design procedures</li> <li>Improvement may be time dependent</li> <li>Surface heave may occur</li> <li>Limitations on how much densification can be obtained</li> <li>Difficulties in placing large charges at great depths</li> <li>Oversized charges may cause cratering of the ground surface, slope failure, or vibration related damage.</li></ul><h2>Key References for this technology:</h2>Ivanov, R.L. (1967). <em>Compaction of Non Cohesive Soils by Explosions </em>(translated from Russian), National Technical Information Service Report No. TT 70-57221, U.S. Dept. of Commerce, Springfield, VA, 211 pp.</p><p>Narin van Court, W.A. and Mitchell, J.K. (1994). “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. (1995). “Soil improvement by blasting: part II.” <em>Journal of Explosives Engineering</em>, Vol. 12, No. 4, pp. 26-34, Jan./Feb.</p></p>