Project Summary
Hanson is providing engineering and scientific services to Ameren Transmission Co. of Illinois on many aspects of the Illinois Rivers Project. The project includes more than 385 miles of new transmission lines from Palmyra, Missouri, to the Indiana border east of Marshall, Illinois. Highlights of our services include:
Geotechnical characterization and flood hazard mapping
The project’s magnitude requires a quickly accessible methodology for determining the physical properties of the soil conditions along the route alignment. To assist with that effort, Hanson used various geographic information system (GIS) databases, collected from multiple public sources, to produce maps that may be used to develop access plans (soil drainage maps) and property easement negotiations (topsoil thickness maps) and identify potential construction issues caused by surface or subsurface geologic conditions (geohazard maps). Hanson also generated geological and flood inundation cross-sections.
Article originally published
in the June 2020 issue of
the FES Journal.
Additionally, Hanson’s water resource engineers developed flood hazard boundaries for streams and rivers that will be crossed by the proposed transmission line routes. The analysis resulted in the determination of the 100- and 500-year flood elevations and 82 significant stream crossings along the entire route. Hanson created corresponding inundation maps (floodplain maps) for these crossings to aid Ameren in identifying possible permitting issues and assisting the project team with layout and design of the proposed pole structures.
Critical access route evaluation
For critical access route evaluation, Hanson screened 7,728 public roadways in 19 Illinois counties to identify those that may be problematic to construction vehicle traffic using access routes along the proposed transmission line. Hanson provided the locations in Google Earth’s KMZ format; a table listing the roadway locations and load capacities or clearance limitations; and a potential detour length for affected construction traffic. Hanson also prepared performance specifications that outlined requirements for roadway planning and use.
Transmission line segments and substation subsurface investigations
Hanson is providing subsurface investigations and foundation designs for more than 2,200 transmission line monopoles for the project line segments. Soil borings began in July 2014 under the sometimes challenging constraints of property access. As of January 2017, the Hanson team has performed subsurface investigations for more than 1,900 foundations. Hanson also performed value engineering on the project, and as an example, realized a savings of 10,000 pounds of reinforcing steel on a single foundation.
"Hanson is a valued partner with Ameren and provides a very high quality product." — Kevin Gerhardt, Ameren Corp.
Hanson also has provided subsurface investigations and foundation engineering recommendations for the nine substations between each segment and four of the substation area connections.
Transmission line segments foundation design
Hanson has provided foundation designs for more than 1,850 monopole structures. Foundation designs have included straight-sided drilled piers, vibratory-driven caissons and soil tie back-augmented drilled piers.
Because of the number of structures, the tight schedules and the multiple and constantly evolving inputs, Hanson’s design process uses database and spreadsheet interaction for maximum efficiency and to reduce the chance of human error. This database allows the necessary design data to be organized, sorted and combined into a standardized format for each foundation.
Pier foundation design comparison and criteria study
Hanson also is in the process of providing a pier foundation design and criteria comparison to Ameren. The general design approach, load factors, deflection criteria and reinforced concrete design procedure used on the Illinois Rivers project are being compared with those typically used by Hanson on other projects. The Hanson team will suggest changes to the Ameren basis of design for drilled pier foundations, with the intent of balancing economy and reliability.
Drilled pier construction quality assurance
Construction quality assurance for monopole foundation construction has been provided for the substations constructed to date and about 1,400 foundations of the transmission line. Construction quality assurance has included on-site observation of pier construction, including observation and evaluation of subsurface conditions during excavation, pier excavations for conformance with the plans and specifications, reporting of field observations and tracking of third-party concrete strength testing.
Permitting
Hanson has performed natural resources field studies and associated permitting and agency coordination support for the nine main substations, the area connections between line segments and substations and the Pana to Faraday and Pana to Austin segments in Christian, Montgomery and Sangamon counties. These lines total about 55 miles of overhead electric transmission line. The project requires careful coordination because of the accelerated schedule and ongoing revisions to the transmission line alignment and access roads. Services include current and historic mapping review, wetland delineations, Indiana bat habitat assessments, coordination with the U.S. Army Corps of Engineers regarding the preliminary jurisdiction determination, U.S. Fish and Wildlife Service habitat assessment reporting, preparation of permit applications for temporary and permanent wetland/waterbody impacts and federal and state agency coordination.
Water resource engineering and related regulatory support services also were completed to assess the alignment of the proposed transmission pole foundations to determine the applicability of Illinois Department of Natural Resources, Office of Water Resources, Statewide Permits for the proposed structures in the FEMA designated floodway or jurisdictional floodway and provide local floodway manager liaison for structures located in a floodway less than 10 square miles.