PROJECT SUMMARY
For the Norco Bluffs Phase 2 Toe Protection project in Santa Ana, California, an earth fill was required to be placed against the existing bluffs, approximately 7,330 feet in length. This embankment is revetted with riprap slope protection and a launchable stone toe blanket. This project will tie into existing high ground at the upstream (Station 90+20) and downstream (Station 19+90) project extents. The embankment fill will raise the grade between 12 and 25 feet above the existing grade to provide protection for up to a 100-year flow event water surface elevation (WSE). The proposed embankment slope is 2H:1V and is revetted with riprap slope protection 42 inches thick, measured perpendicular to the slope face. The expected scour is between 5 and 14 feet below the existing thalweg (between 6 and 19 feet below the existing grade at the project alignment). Excavation is planned to reach 2 feet above the typical groundwater, averaging 5 feet below the existing grade, to eliminate the need for dewatering. A launchable stone toe is intended to provide protection from scour, with the stone toe being 9 feet high and varying in width between 10 and 30 feet, depending on the expected scour depth along the project alignment.
SOLUTION
The contractor, Griffith, faced a challenge when quicksand conditions were encountered during preliminary work in 2019. A track-mounted drill rig and a track support vehicle were used for the work. After the completion of the last boring, the Morooka became stuck in loose, saturated sand, where the groundwater level was very close to the surface. Despite several attempts to free the vehicle, including towing with a D-4 and D-6 dozer and excavation around the vehicle, the excavation only caused the vehicle to sink deeper into the saturated sand, creating a large void that filled with groundwater, essentially trapping the equipment in quicksand.
Layfield was contacted and was able to provide 50 rolls of Mirafi® RS580i and another 50 rolls of FW300. The Mirafi® RS580i material provided superior reinforcement strength, soil interaction, high water flow, and soil retention capabilities. The material was laid directly on the roadbed, with backfill placed directly on top, allowing trucks to drive over the area without sinking. The FW300 geotextile was used for the slopes as per the project design.
CHALLENGES & RESULTS
The main challenge of the project was dealing with the quicksand conditions encountered during the preliminary work, which caused the Morooka to become stuck in the saturated sand. Despite multiple attempts to remove the vehicle, excavation worsened the situation. The solution provided by Layfield’s Mirafi® RS580i material enabled the contractor to continue the project without further complications. The reinforcement allowed heavy machinery to safely drive over the roadbed and slopes, ensuring the project proceeded smoothly and without further delays.