Compaction Grouting of Loose Soil Beneath the West Coast's Largest Dry Dock

The base slab of the largest dry dock on the west coast of the United States has experienced up to 5 inches of differential settlement under loading from large ships since its construction in the early 1960s. This settlement has resulted in a large depression in the dry dock floor. Soil borings and other geotechnical tests revealed a loose soil zone beneath the depression. Following geotechnical analyses and comparison of options, compaction grouting was judged to be the most appropriate method to improve the loose soils and mitigate ongoing settlement without requiring major structure repair or replacement of the dry dock base slab. Compaction grouting was performed in 2006 to densify the loose soil and extend the life of the dry dock structure. The design of the compaction grouting system from preliminary to final design, changes during construction, and grout operations and results are presented.