Geologic Exploration for Ground Classification: Widening of the I-70 Veterans Memorial Tunnels

The Colorado Department of Transportation (CDOT) recently completed widening of the Interstate 70 (I-70) Veterans Memorial Tunnels located one mile east of Idaho Springs, Colorado. As the geotechnical consultant, Yeh and Associates (Yeh) performed a detailed subsurface investigation to develop a rock mass classification using the Rock Mass Rating System (RMR) and Tunneling Quality Index (Q-rating). The goal of the investigation was to develop a rating system that could be used to predict the strength characteristics of the tunnel rock to be mined. Following years of increasing traffic volume during the summer and winter tourist seasons, CDOT implemented a plan to widen the existing eastbound tunnel an additional 21 feet in an effort to reduce persistent gridlock. The addition of an eastbound third lane on I-70 from East Idaho Springs to the bottom of Floyd Hill would reduce travel time and backups en route to the Denver-metro area. Yeh’s investigation began with a review of historical Colorado Highway Department (CHD) documents including geologic maps, technical memorandums and tunneling photos. Yeh implemented traditional and specialty site investigation methods to characterize the rock mass which would allow the tunnel design team to develop ground support and baseline conditions. Investigation methods included geologic and structural mapping of rock outcrops; drilling and logging rock core borings; borehole camera inspection of the drilled borings; and a three-dimensional seismic reflection tomography survey. Field data and lab test results correlated to observed conditions from the investigation were used to produce geologic maps showing estimated RMR, Q-ratings and rock types. Using the geologic maps provided by Yeh, the other members of the tunnel design team produced a ground classification map and associated excavation parameters. These documents were the foundation for preliminary cost estimates and project scheduling by the tunnel construction company. Following completion of the project, Yeh compiled a geologic map of observed as-built conditions of the eastbound bore to compare against predicted conditions.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; Photos; References; Tables;
  • Pagination: pp 411-430
  • Monograph Title: Proceedings of the 67th Highway Geology Symposium (HGS 2016)

Subject/Index Terms

Filing Info

  • Accession Number: 01630382
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Mar 9 2017 1:00AM