GEOPHYSICAL MEASURES RELATED TO TUNNELING

LAKE HURON TUNNEL IS THE SCENE FOR AN EXPERIMENTAL PROGRAM IN GEOPHYSICAL METHODS TO DETERMINE THE THICKNESS OF ROCK ABOVE THE CROWN OF THE TUNNEL AND TO IDENTIFY ANOMALOUS GEOLOGIC CONDITIONS. THE LAKE HURON TUNNEL IS BEING BORED THROUGH ANTRIM SHALE WHICH IS A DENSE MARINE SHALE OF MISSISSIPPIAN OR DEVONIAN AGE. THE GEOPHYSICAL METHODS THAT WERE UTILIZED ARE: (1) ELECTRICAL RESISTIVITY TESTS FOR (A) MEASURING GROSS ELECTRICAL PROPERTIES, (B) IDENTIFYING ANOMALOUS GEOLOGIC CONDITIONS, (C) DETERMINING THE INFLUENCE OF THE TUNNELLING MACHINE, AND (D) DESIGNING AND IMPLEMENTING AN INSTRUMENTATION PROGRAM: THIS METHOD PROVED TO BE SUITABLE FOR DISCOVERING UNUSUAL GEOLOGIC CONDITIONS AND FOR REVEALING THE ROCK THICKNESS. HOWEVER, DUE TO THE SPACING AND THE SHAPE OF THE ELECTRODES LOCATED ON THE CUTTER HEAD AND THE DUST SHIELD, PENETRATION IS LIMITED. (2) SUBAUDIBLE ROCK NOISE (SARN) TESTS ARE DESIGNED TO PREDICT THE STRESS OR DISTRESS IN THE WALLS AND FACE OF THE TUNNEL; MICROACOUSTIC NOISES GENERATED IN ROCK AS INTERNAL STRESSES ARE RELIEVED AND RECORDED. AN INVERSE RELATIONSHIP EXISTS WHEREBY A HIGH RATE OF MICROACOUSTIC PULSES INDICATES A HIGH RATE OF STRESS RELIEF OR RELAXATION OF THE ROCK MASS, WHILE A LOW RATE INDICATES THAT THE ROCK MASS IS APPROACHING, OR HAS ACHIEVED, A STATE OF EQUILIBRIUM. BACKGROUND NOISE HAS BEEN A PROBLEM.

Media Info

  • Features: Figures; Tables;
  • Pagination: p. 195-208
  • Serial:
    • Volume: 1

Subject/Index Terms

Filing Info

  • Accession Number: 00236534
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jan 11 1974 12:00AM