Abstract:
The proposed presentation will detail how micropiles with innovative high-rise steel pile caps provided a unique solution to support the replacement of a damaged electric transmission structure located in an existing reservoir.
In March 2021, the utility client identified a damaged and leaning steel lattice transmission tower on a 161 kV transmission line. The structure was located within the Harry S. Truman Reservoir outside of Clinton, MO, and was supported by drilled pier foundations with approximately nine feet of above-ground projection; however, the observed water level was above the top of the foundations. The apparent cause of damage was attributed to debris contacting the tower during recent flood events. A fast-tracked structure and foundation replacement would be necessary to restore the integrity of the line.
Initial concerns with access to the structure location, working under the existing conductors, and the presence of relatively shallow shale bedrock ruled out more traditional drilled pier and vibratory caisson foundations. Ultimately, micropile foundations with steel pile caps were chosen for the replacement construction. Foundations were designed to accommodate nearly 16-foot foundation reveals along with an additional 7 feet of theoretical soil loss from potential scour events. In addition to the static structure loading, foundations were analyzed with hydrodynamic and debris impact forces caused by future flood events.
The foundation contractor was initially contacted mid-April 2021 and worked quickly to develop preliminary foundation designs and construction estimates for the utility client. With ongoing coordination with the utility client and structure designer, detailed foundation designs began in June and final designs were issued for construction early September. Following a lengthy materials procurement schedule, foundation drilling began on January 13, 2022 and steel pile cap installations on all four foundations was completed on January 24.