Ground Improvement for Liquefaction Mitigation at Sevier Bridge Dam

The downstream portion of Sevier Bridge Dam in central Utah was rehabilitated as to provide adequate seismic performance under the State of Utah dam safety requirements. Part of this work included installing stone columns (“granular columns”) into foundation soils to mitigate liquefaction. This ground improvement method was selected over an excavation-and-replacement option, being less expensive and risk-prone in not needing an extensive dewatering system for excavations. Project specifications were developed by the project design team with an eye toward addressing certain shortcomings encountered by team members on other projects. A unique aspect of this installation was use of an aggregate gradation which was more filter compatible with the foundation soils than the contractor’s preferred gradation. The contractor elected to use primary and secondary stone columns, an approach which appeared to be quite effective in meeting improvement (densification) requirements as demonstrated in nine paired pre- and post-improvement cone penetration test soundings.