Dynamic Compaction Solutions for the Redevelopment of the BNSF Tacoma Railyard
The historic BNSF Tacoma Railyard, located in the South Tacoma neighborhood, is being converted into a multi-structure industrial complex. The site geology consists primarily of granular fill materials extending from the ground surface to approximately 12 feet below grade. Beneath the fill lies glacially deposited sand and gravel, known as the Tacoma Formation.
The project includes four warehouse structures, with Building A planned as a 600,000-square-foot facility in the northern section of the property. Approximately half of Building A’s footprint is situated within highly contaminated zones of the fill soils, primarily impacted by heavy metals.
To address the site’s geotechnical challenges, the majority of fill soils across the site are excavated and recompacted to meet the necessary bearing capacity and long-term settlement needs. To meet these geotechnical requirements, Malcolm Drilling was contracted to perform deep dynamic compaction (DDC) on the affected portion of the Building A footprint.
The dynamic compaction process involved repeatedly dropping a heavy weight to generate impact energy for ground densification. Drops occurred in a primary and secondary pattern, with each drop point receiving multiple weight impacts. As dynamic compaction progressed, crater depth was recorded, and a post-improvement site survey was conducted to assess the effect of the dynamic compaction on the fill soils. Following treatment, the subgrade was confirmed to meet the required compaction criteria, enabling construction of Building A to proceed.
