Rockfall Hazard Mitigation at the TH-53 Bridge, Virginia, Minnesota

The Trunk Highway 53 (TH-53) Relocation Project near Virginia, Minnesota, includes a new bridge across the currently inactive Rouchleau Mine Pit, one of many open pit iron ore mines on the Mesabi Range. Rockfall hazards associated with the existing highwall on the east side of the Rouchleau Pit were assessed and mitigated to ensure construction worker safety and long-term performance of the bridge. This paper provides a brief geologic background and describes the process of assessing and mitigating rockfall hazards at the TH-53 bridge site. Rockfall hazards were primarily assessed on the basis of observations made during site visits, including: geologic feature mapping, assessment of existing talus, identifying rockfall sources and travel paths, and run-out distance assessment via trial rolling of rocks. The influences of the local geologic conditions of the Biwabik Iron Formation at the site and the highwall geometry result in the potential for several mechanisms of rockfall hazard at this site, and the extreme northern climate contributes to the hazard through freeze-thaw conditions which initiate rockfall events. Rock bounce heights and velocities were analyzed using the Colorado Rockfall Simulation Program (CRSP). Mitigation elements for the protection of workers constructing the east pier of the bridge, which is located on a bench cut into the eastern pit highwall, include an attenuator fence system and combined wire mesh and cable net drapery covering portions of the highwall face. A soil berm will provide long-term protection for the eastern bridge pier. Details of the mitigation system and its construction are described, including: element selection and sizing, site-specific details, anchor design, challenges to construction, and quality control.


  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; Photos; References; Tables;
  • Pagination: pp 202-221
  • Monograph Title: Proceedings of the 67th Highway Geology Symposium (HGS 2016)

Subject/Index Terms

Filing Info

  • Accession Number: 01628000
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Mar 1 2017 9:04AM