COLORADO STRAIGHT CREEK TUNNEL-I-70

THE COLORADO DIVISION OF HIGHWAYS IS BUILDING A 1.7 MILE VEHICULAR TUNNEL UNDER THE CONTINENTAL DIVIDE AT AN ELEVATION OF SLIGHTLY OVER 11,000 FEET. IT IS THE WORLD'S HIGHEST VEHICULAR TUNNEL, THE LONGEST VEHICULAR ROCK BORE IN NORTH AMERICA, AND THE WORLD'S HIGHEST MECHANICALLY VENTILATED TUNNEL. THE PROJECT INCLUDES DRIVING THE FIRST OF WHAT WILL EVENTUALLY BE TWIN BORES, CONSTRUCTING COMBINATION VENTILATION AND PORTAL STRUCTURES FOR BOTH TUNNELS, STUB SECTIONS OF WHAT WILL BE THE SECOND TUNNEL, THREE CROSS PASSAGE WAYS BETWEEN THE VEHICULAR AND PIONEER TUNNEL AND OTHER ITEMS NECESSARY TO PRODUCE AN OPERATIONAL TUNNEL BY 1971. THE WESTBOUND TUNNEL WILL BE USED FOR TWO-WAY TRAFFIC UNTIL THE PIONEER BORE IS ENLARGED LATER TO BECOME THE EASTBOUND TUNNEL. THIS LINK IN I-70'S PROGRESS WILL SAVE THE HIGHWAY USER TEN MILES AND AS MUCH AS FORTY MINUTES. BEDROCK IN THE STRAIGHT CREEK TUNNEL AREA CONSISTS OF ABOUT 75% GRANITE AND ABOUT 25% METASEDIMENTARY GNEISS AND SCHIST OF PRECAMBRIAN AGE. THE TUNNEL AREA IS WITHIN THE LOVELAND FAULT ZONE, AND THE BEDROCK IS CUT BY NUMEROUS FAULTS AND SHEER ZONES RANGING FROM LESS THAN A FOOT TO 600 FEET, SEPARATED BY LESS INTENSIVELY SHEARED ROCK. THE EAST PORTAL AREA OFFERED ANOTHER PROBLEM: A BIG LANDSLIDE LIES ON THE SLOPE TO THE NORTH OF THE PORTAL. DURING CONSTRUCTION OF THE PILOT BORE, GROUNDWATER FLOWS WERE ENCOUNTERED IN MODERATELY SHEARED ROCK. THE PILOT TUNNEL HAS OFFERED A BONUS FUNCTION IN ADDITION TO THAT OF ENGINEERING GEOLOGY: DRAINAGE. COMPUTATION AND TESTS WERE MADE OF CARBON MONOXIDE POUNDS EMITTED PER MINUTE BY AN IDLING MOTOR AND CARBON MONOXIDE POUNDS PER MILE BY THE POWER PLANTS OF MOVING VEHICLES. THE APPROXIMATE AVERAGE CARBON MONOXIDE EMISSION WAS COMPUTED. VENTILATION SYSTEMS WILL BE OF A TRANSVERSE DESIGN TO DELIVER FRESH AIR AT THE ROADWAY LEVEL. EXHAUST AIR WILL BE DRAWN INTO THE EXHAUST DUCT THROUGH CEILING OPENINGS. TRAFFIC CONTROL DEVICES WILL OPERATE TELEVISION SURVEILANCE WHEREBY THE TRAFFIC MOVEMENT CAN BE MONITORED AT ALL TIMES. A WALKWAY CAR FOR RAPID TRANSIT OF PERSONNEL TO THE SCENE OF AN ACCIDENT OR STOPPAGE WILL BE PART OF THE TUNNEL EQUIPMENT. CONVENTIONAL CONSTRUCTION METHODS ARE BEING USED TO ACCOMPLISH THE TOP HEADING AND BENCH PORTIONS OF THE EXCAVATION THROUGH APPROXIMATELY 7,100 FEET OF COMPETENT ROCK. LESS TRADITIONAL METHODS ARE USED IN THE 1,085 FEET OF EXTREMELY BAD GROUND IN THE CENTER OF THE MOUNTAIN. THEY ENTAIL THE USE OF A HUGE SHIELD THAT ALLOWS THE DRIVING TO CONTINUE FULL FACE.

  • Supplemental Notes:
    • Vol 48, No 4, PP 14-19, 2 FIG, 6 PHOT
  • Authors:
    • Shumate, C E
  • Publication Date: 1969-10

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Filing Info

  • Accession Number: 00215301
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Aug 26 1970 12:00AM