USACE reconstructed some levee cutoff walls within the Sacramento River Area during the past two years. The levee cutoff wall is constructed by a mixture of cement, bentonite, and slag, which is a low permeability and high strength material. However, it becomes brittle as well. Under an event of flood or earthquake, the levee may deform due to the external load and the performance of the wall needs to be assessed for its integrity after the event. By embedding an optical fiber sensor into the cutoff wall vertically during construction, the long-term health monitoring of the SCCB cutoff wall at Natomas Reach I started to be conducted from July. 9th, 2020. The curing process was monitored continuously during the first seven days after the SCCB wall construction. Weekly reading is currently taken to measure the final stage of heat dissipation and strain development. The monitoring will continue for years to evaluate the performance of the SCCB wall under the embankment construction, the flooding event, the earthquake event, and the operation of Garden Highway.
The goal of this project is to examine the feasibility of DFOS technology to improve the understanding of the long-term performance of seepage cutoff walls made of slag cement-cement-bentonite (SCCB) mixture. In this study, fiber optics cables were installed vertically inside an SCCB wall, as shown in Figure 4, to measure strain and temperature changes from the construction stage to the in-service stage. The following evaluations have been made from the optical fiber data obtained along the two sides of the wall:
- Wall integrity: Using the temperature data obtained during the cement hydration and curing phase, thermal integrity test was conducted to evaluate the wall widths at different depths.
- Settlement: The axial strain profiles at three instrumented sections of the wall were measured using a pair of strain cables installed inside the sections. The in-situ settlement profiles were evaluated by integrating the measured axial strain profiles.
- Bending and lateral movements: Bending strain (or curvature) profile can be deduced from the strain data of the fiber optic sensing cables placed at the two sides of the wall. The lateral movements of the wall can be evaluated by performing double integration of the curvature profiles.
Collaborator: US Army Corps of Engineers (USACE)
Researchers: Ruonan Ou, Andrew Yeskoo, John Murphy, Yaobin Yang, Kenichi Soga (UC Berkeley), Linqing Luo (LNBL)
Domains: Water Infrastructure
Capabilities: Distributed Fiber Optic Sensing (DFOS) – Distributed Strain Sensing (DSS), Distributed Temperature Sensing (DTS)