Sevier Bridge Dam Rehabilitation Phase II

In 2003, a geotechnical design report initiated the Phase I project of upstream dam improvements. This report found that additional work (to be completed as part of a future Phase II) was needed on the crest and downstream embankment due to liquefiable soils beneath the downstream toe, which posed a failure risk during the regulatory design earthquake. Once funding for Phase II became available, Gerhart Cole, Inc. performed additional studies that indicated successful stabilization of the embankment could be accomplished by improving the liquefiable soils and constructing a downstream stability berm. Separate hydraulic analyses showed the existing spillway would also need to be enlarged. Phase II rehabilitation began in Fall 2022. This paper discusses several geotechnical aspects of the work, namely:
•Excavating the downstream embankment,
•Mitigating liquefiable soils using granular columns,
•Constructing a stability berm and filter/drain system on the improved soils, and
•Using a bio-polymer slurry trench along the crest to create a sand filter to address cracking.