Evaluating Ground Improvement after Blast Densification: Performance at the Oakridge Landfill
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 142, Issue 1
Abstract
Blasting has long been used as a ground improvement technique to densify loose granular soils. Explosives detonated at depth induce liquefaction in the target sand followed by pore pressure dissipation and attendant consolidation. Improvement typically is verified via measured surface settlements and increased penetration resistance with in situ tests such as the cone penetration test (CPT). However, an increase in penetration resistance is often not observed for months or even years after blasting. The results of instrumentation at a production blast zone at the Oakridge Landfill are reported herein. Instrumentation included surface settlements, pore pressure measurements inside and outside the blast zone, preblast and postblast piezocone () soundings, and gas concentrations of pore fluid. No increase in penetration resistance with the was detected 53 days after the final blast, despite more than 0.5 m of settlement and an increase in relative density to 80% or more in some areas. Results of gas chromatography tests on the collected pore fluid samples showed that gas produced by the explosives was trapped in the target layer and saturated the groundwater with . Consequently, no more could dissolve into solution, and gas existed as occluded bubbles. The presence of occluded bubbles created an unsaturated condition, which in turn affected the mechanical behavior of the densified soil and reduced the CPT tip resistance during postblast testing.
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Acknowledgments
Funding for this study was provided by the National Science Foundation through Grant No. CMMI 1235440. The support of Dr. Richard Fragaszy, program director at NSF, is greatly appreciated. The authors would like to thank Waste Management for allowing access to the site. In addition, the authors would like to thank Dr. Robert Bachus and Dr. Majdi Othman of Geosyntec Consultants for their interest and help with this work, and Mr. Will McBryde of GeoSyntec Consultants and Randy Phillips of AE Drilling for their help and cooperation during the field portion of this study.
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© 2015 American Society of Civil Engineers.
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Received: Aug 12, 2014
Accepted: May 4, 2015
Published online: Jul 6, 2015
Discussion open until: Dec 6, 2015
Published in print: Jan 1, 2016
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