Sacramento River East Levee Contract 4 – Seepage Cutoff Wall Construction Challenges and Solutions

Improvements to portions of the Sacramento River East Levee (SREL) were made as part of the American River Common Features (ARCF) 2016 Project. The work is significant due to its location and importance for public safety and flood risk reduction to critical infrastructure in Sacramento, California. This paper focuses on construction of seepage cutoff walls at four separate locations along SREL in 2023 and 2024 in an urban environment as part of the fourth construction contract of a multi-contract project.
This paper discusses the challenges encountered and solutions adopted during jet grout and deep mix method (DMM) cutoff wall construction. The paper emphasizes the importance of collaboration during construction, construction sequencing, challenges created by triple fluid jet grouting adjacent to an existing cutoff wall and in levee breach fill, and the solutions developed to overcome those challenges. Triple fluid jet grouting was selected to close a 200-foot-long gap beneath a 100-foot-deep existing seepage cutoff wall, which required a vertical and horizontal overlap. Challenges included jet grouting to a depth of 140 feet through gravels, cobbles, and buried trees and verification of the required overlaps. A second triple fluid jet grout cutoff wall was constructed through a 100-year-old levee breach adjacent to a privately owned hospitality facility. Jet grouting through the breach fill was problematic with grout losses, shallow sinkholes, and difficult drilling conditions. Supplemental single fluid jet grout stabilization columns, staged grouting, and extensive monitoring were performed to help prevent damage to the nearby structures. DMM was used to replace a proposed open trench soil-bentonite cutoff wall and to replace a proposed jet grout cutoff wall. In each case, accessibility and reduced schedule were the main driver for there placement. Contract flexibility was important to allow for these changes. Jet grout cutoff wall verification was done through verticality readings of each column, graphical overlap reports, coring, and in situ testing. All elevations in this paper refer to the North American Vertical Datum of 1988 (NAVD 88).