GEOLOGIC RESEARCH AT THE STRAIGHT CREEK TUNNEL SITE, COLORADO

THE COST OF CONSTRUCTING TUNNELS IN THE FRONT RANGE OF COLORADO, AND IN MANY OTHER PLACES IN THE WORLD, HAS USUALLY EXCEEDED THE ESTIMATES OF THE COST, SOMETIMES BY A WIDE MARGIN. IN MOST INSTANCES THE REASON FOR THE INCREASED COST HAS BEEN GEOLOGIC. A RESEARCH PROJECT AT THE STRAIGHT CREEK TUNNEL SITE ON INTERSTATE 70 WAS CONDUCTED TO APPLY AND EVALUATE NEW IDEAS IN THE USE OF GEOLOGY AND GEOPHYSICS FOR THE PREDICTION OF GEOLOGIC CONDITIONS AT DEPTH, IN THE BELIEF THAT MORE ACCURATE PREDICTIONS OF GEOLOGIC CONDITIONS CAN REDUCE THE COST OF CONSTRUCTION. THE SURFACE OUTCROPS IN THE VICINITY OF THE TUNNEL WERE MAPPED IN DETAIL, PARTICULAR ATTENTION BEING GIVEN TO THE PERCENTAGE OF DIFFERENT ROCK TYPES, THE ATTITUDE OF THE FOLIATION OF THE ROCK, AND THE ATTITUDE AND SPACING OF FAULTS AND JOINTS. THE SURFACE OBSERVATIONS WERE SUPPLEMENTED BY THE DRILLING AND LOGGING OF TWO CORE HOLES. RECORDS WERE KEPT AS TO THE PERCENTAGE OF ROCK TYPES, THE ATTITUDE OF THE FOLIATION, AND THE ATTITUDE AND SPACING OF FAULTS AND JOINTS. GEOLOGIC INVESTIGATIONS WERE SUPPORTED BY GEOPHYSICAL LOGGING OF THE DRILL HOLES, INCLUDING RESISTIVITY, GAMMA-RAY , AND GAMMA-RAY DENSITY, BY SEISMIC PROFILES AT THE SURFACE RUN PARALLEL AND AT RIGHT ANGLES TO THE TUNNEL LINE, AND BY THE LABORATORY MEASUREMENT OF PHYSICAL AND ENGINEERING PROPERTIES OF SAMPLES FROM THE SURFACE AND THE DRILL HOLES. FROM THESE DATA A STATISTICAL MODEL OF THE GEOLOGY AT TUNNEL LEVEL WAS CONSTRUCTED. IT WAS THEN POSSIBLE TO CALCULATE THE PROBABLE ROCK LOADS, AND THE SPACING OF SETS, THE SPACING OF LAGGING, THE PROBABLE SECTIONS OF THE TUNNEL THAT SHOULD BE TESTED BY FEELER-HOLES, THE PROBABLE AMOUNT OF GROUT THAT WOULD BE REQUIRED TO SEAL BADLY BROKEN GROUND HIGHLY SATURATED WITH WATER, THE PROBABLE AMOUNT OF WATER THAT WOULD FLOW FROM THE PORTAL OF THE TUNNEL AS THE FACE WAS ADVANCED, AND THE PROBABLE INITIAL AMOUNT OF WATER THAT MIGHT BE EXPECTED TO FLOW FROM A FAULT ZONE WITHIN ANY INTERVAL OF THE TUNNEL. /AUTHOR/

Media Info

  • Media Type: Print
  • Features: Figures; References;
  • Pagination: pp 18-34
  • Monograph Title: Construction on marsh deposits; Tunnel site geologic research; Ground water control; Presplit blasting
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00233658
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Dec 12 1994 12:00AM