<p><p><div><img class="wp-image-3348 size-full aligncenter" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph of the Highway 504 bridge over Coldwater Creek in Washington state after potentially liquefiable soils were improved through blast densification." width="500" height="332" /></div><div><h2>Project Summary/Scope:</h2>The proposed bridge along State Route 504 over Coldwater Creek was to be constructed on debris-flow soils originating from the eruption of Mt. St. Helens. The potentially liquefiable soil was improved through the use of blast densification.</p><p>Subsurface Conditions: 130 feet of debris flow from the 1980 Mt. St. Helens’ eruption. The debris flow contained very loose silty sand and gravel with boulders and cobbles. The material was potentially liquefiable during a seismic event.</p><p>A test program showed an average of 0.9 feet of settlement on the first pass of blasting. Between 3 and 5 feet of settlement was expected. Increasing the charge on the second pass produced an additional 0.7 feet of settlement. During production blasting, the charge was increased so blast induced ground settlements averaged 5 feet. Spread footings were found adequate following ground improvement.<br><h2>Alternate Technologies:</h2>Other ground improvement techniques considered include vibro-replacement, deep soil mixing, jet and compaction grouting, and deep dynamic compaction.<br><h2>Performance Monitoring:</h2>Becker penetration tests were used to determine liquefaction resistance.</p><p><img class="wp-image-3349 size-full aligncenter" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="" width="677" height="462" /><h2>Case History Author/Submitter:</h2>Washington State Department of Transportation (WSDOT)<br>Environmental and Engineering Programs<br>310 Maple Park Ave. SE<br>Olympia, WA 98504-7323<br><h2>Project Technical Paper:</h2>Schaefer, V., Abramson, L.W., Hussin, J.D., and Sharp, K.D. (1997). “Ground improvement, Ground reinforcement, Ground treatment: Developments 1987-1997,” Proceedings of sessions sponsored by the committee on soil improvements and geosynthetics of The Geo-Institute of the American Society of Civil Engineers in conjunction with Geo-Logan ’97, Geotechnical special publication No. 69. ASCE, New York.<br><h2>Date Case History Prepared:</h2>November 2012</p><p></div></p></p>