Blast Densification for Mitigation of Dynamic Settlement and Liquefaction

摘要

A loose, debris avalanche deposit, resulting from the 1980 eruption of Mt. St. Helens, was encountered during the foundation geotechnical investigation for Bridge 12 on the Spirit Lake Memorial Highway (SR 504) in the Mt. St. Helens National Volcanic Monument, Washington. The deposit was determined to be at risk of experiencing liquefaction and/or dynamic settlement during the design seismic event for the structure (Richter magnitude 6.5 and peak ground acceleration 0.55g). The experimental use of deep blasting was selected by the Washington State Department of Transportation, and approved by the Federal Highway Administration, to densify the deposit full depth (up to 43 meters) for the purpose of mitigating the liquefaction and dynamic settlement risks. The contract for the work utilized a test section to evaluate the blast design. Revisions were made to the blast design based on the results of the test section blasting, and production blasting was completed in December of 1992.