Deep Dynamic Compaction:Practical and Cost-Effective Ground Improvement at the Port of Long Beach

This paper highlights geotechnical challenges related to the design and construction of a new 5,300 square-meter (57,000 square-foot), two-story maintenance facility for the Port of Long Beach, California. The 70,000-square-meter (17-acre) site is part of land reclaimed in the early 1950's from the Pacific Ocean and filled with compressible and liquefiable hydraulic fill. The remnants of a previous rock dike and dumped construction rubble were also found within the hydraulic fill representing the former limits of the landfill. To mitigate the impacts of soil liquefaction during a seismic event, a comprehensive study was performed to evaluate alternatives for ground improvement. Considering the buried rock/rubble, proximity of existing structures and underground oil lines and the sustainability of the solution, Deep Dynamic Compaction (DDC) was selected. The DDC process used a 118-Mg (130-ton) crawler crane with multiple drops and passes of a 27.2-Mg (30-ton) tamper weight falling 24.4 m (80 feet). Ground vibrations caused by DDC can be potentially damaging to nearby improvements, as well as annoying to people. Several velocity sensors were installed across the site and near existing structures to record peak particle velocities at various distances from the tamping points and evaluate vibration impacts to nearby improvements. In addition, a vibration isolation trench was excavated along one property line in an effort to further reduce vibration impacts. Implementation of sustainable design practices including reduction of concrete materials required for foundation construction, reuse of soil, construction debris, aggregate base, and recycling of pavement materials are also discussed. DDC was found to be a simple, fast, practical, and cost-effective technique for ground improvement based on site-specific conditions and the intended use of the site.