Sevier Bridge Dam is located along the Sevier River near Scipio, Utah. The structure was originally constructed between 1903 and 1907 and then enlarged between 1913 and 1916. The embankment is 1,340 feet in length at the crest and has a structural height of 92 feet. The Sevier Bridge Dam impounds approximately 236,000 acre-feet of water and is the largest privately owned and operated reservoir in Utah. The reservoir provides water for irrigation in central Utah.
In 2003, a geotechnical design report initiated the Phase 1 project for upstream improvements of the dam. During this study it was found that additional work would be needed on the crest and downstream portion of the embankment. Liquefiable soils were found below the downstream toe, and analyses indicated that during the regulatory design earthquake, the embankment would likely fail. Geotechnical FLAC modeling suggested that improving the liquefiable soils and constructing a downstream stability berm could stabilize the embankment. There was also a concern that during a major seismic event the embankment would crack.
Hydraulic analyses performed by Bowen Collins & Associates identified the need to enlarge the spillway to handle the design flood. Bedrock uncertainties at the spillway required additional study to determine the bedrock condition and bearing capacities. The new spillway configuration required a new embankment to connect the right spillway wall to the bedrock abutment. Seepage would have to be controlled in this new embankment.
Rehabilitation of the spillway and downstream slope of the embankment began in Fall 2022. Key aspects of the project included: a) excavating one third of the downstream embankment, b) improving liquefiable soils using granular columns, c) constructing a stability berm and filter and drain system over the improved soils, d) excavating a bio-polymer slurry trench along the crest and backfilling with filter sand to address cracking, e) cleaning and sealing bedrock below structural concrete, f) grinding bedrock abutments to a surface that could be backfilled and compacted against, f) controlling seepage on the right embankment of the spillway using fine-grained, low permeability clays, and g) installing a filter and drain system at the right abutment of the spillway to protect the embankment. This presentation focuses on the design and installation of the granular columns and overlying stability berm, as well as the bio-polymer slurry trench. Implementation of these mitigation measures demonstrate minimum standards were met and increased the seismic resiliency of the dam.
