Mount Baker Ridge Tunnel is being built in Seattle, to an external diameter of 25.3 m from the perimeter inwards by the stacked drift methd. Small horshoe section drifts at 2.9 m centres are being driven around the bore's circumference then filled with concrete to form a permanent lining. The 400 m long tunnel is being bored to take two roadway levels of a new interstate highway through the ridge in the least destructive manner. Piled circular access pits were firstly built at both portals, and then broken through using a roadheader. Subsurface settlement, which was limited to 25 mm was found to be 75 mm on the second drift at a depth of 60 m. This level was repeated in the third drift without any explanation, but the specified level has not been exceeded since. On average, 15 days are taken to reach the far portil when the 55 ton backhoe shields are carried round by truck. Concrete is pumped along a slick line suspended from the crown and withdrawn as the drift fills. A design review board and a disputes review board have been set up to settle any unexpected issues on site. (TRRL)

Media Info

  • Features: Figures; Photos;
  • Pagination: p. 29-31
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00395511
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD, TRIS
  • Created Date: Oct 31 1985 12:00AM