Compaction Grouting to Mitigate Settlement beneath Approach Fills, California State Route 73 at Laguna Canyon Road

California State Route 73, also known as the San Joaquin Hills Transportation Corridor, is a 24-km long toll highway connecting the cities of San Juan Capistrano and Newport Beach, in Orange County, California. The design/build project included 78 structures and more than 12 km of retaining walls and sound walls. Structures range from 1- and 2-span bridges to connecting structures spanning over 0.8-km with 13 support locations. Special designs were required to span zones of loose, wet alluvial soils. One of the interchanges located at Laguna Canyon Road incorporated two ramps to be constructed over a (proposed) drainage culvert. Soil investigations revealed that underlying deep alluvial soils possessed both a static settlement potential, and a dynamic consolidation potential in excess of Caltrans' design criteria. Several remedial construction approaches were considered, although the presence of a critical water supply pipeline in the proposed construction area narrowed the method selection to "low-impact" techniques. Compaction grouting was selected upon completion of a test section, and included treatment of the alluvial profile at a 1:1 projection from the proposed culvert structure. Precision monitoring of the buried water supply line was required during proximal grouting treatment. Project totals included 921 grout injection points, 3,360 m³ of limited mobility displacement grout and more than 14 km of grout casing installed. Average post-treatment CPT "n"-values were well in excess of project specification minimums.