TUNNEL SURVEY, PART II

WHEN DRIVING A TUNNEL IT IS SOMETIMES NECESSARY TO DRIVE A PILOT TUNNEL FOR REASONS OF SOIL INVESTIGATION, SOIL TREATMENT, ETC. THE SURVEY CAN BE ADJUSTED ON HOLING THROUGH AND SURVEY STATIONS ESTABLISHED ALONG THE LENGTH OF THE PILOT TUNNEL TO FACILITATE GUIDING OF THE MAIN SHIELD. CONTROL OF THE TUNNEL FACE WHILE DRIVING ENTAILS KEEPING A TIGHT CHECK ON SIX THINGS: (1) THE LINE-TO INSURE THE TUNNEL IS IN THE CORRECT POSITION IN THE HORIZONTAL PLANE, (2) THE LEVEL-TO ENSURE THE TUNNEL IS IN THE CORRECT POSITION IN THE VERTICAL PLANE, (3) THE SQUARE-TO ENSURE THAT THE SHIELD IS POINTING IN THE CORRECT DIRECTION HORIZONTALLY, (4) THE PLUMB - TO ENSURE THE SHIELD IS POINTING IN THE CORRECT DIRECTION VERTICALLY, (5) THE ROLL - TO ENSURE THE KEY IS IN THE CORRECT POSITION, AND (6) THE SHAPE - TO ENSURE THE TRAMMEL IS CORRECT, I.E. THE TUNNEL IS CIRCULAR. WITH THE DEVELOPMENT OF ADVANCED MECHANICAL HANDLING IN TUNNELLING TECHNIQUES, THE ADVANCE OF THE TUNNEL FACE HAS BEEN SUCH THAT MORE SPEEDY TECHNIQUES WERE REQUIRED TO KEEP PACE. SCALES FIXED TO THE REAR END OF THE SHIELD ARE USED SUCCESSFULLY TO SURVEY THE POSITION OF THE SHIELD FROM A KNOWN SURVEY STATION. A THEODOLITE AND A LEVEL ARE USED TO KEEP A CHECK ON LEVEL. CONTROL OF PLUMB AND ROLL IS KEPT USING A PLUMB BOB ON THE SHIELD. A VISUAL DISPLAY SYSTEM GIVING A PREDICTED POSITION OF THE SHIELD 8FT IN FRONT OF THE FACE WAS DEVELOPED. THIS PREDICTOR SYSTEM CONSISTS OF A SERIES OF MIRRORS SO LOCATED ON THE FACE THAT A BEAM OF LIGHT PROJECTED FROM A LIGHT BOX IS REFLECTED ON TO A SCREEN BY THE SHIELD DRIVER'S CONTROLS. THE LASER HAS BEEN USED AS A LIGHT SOURCE IN THE UNITED STATES ON ONE OR TWO TUNNELS. SPECIAL PROBLEMS ARE DISCUSSED RELATING TO THE SETTING OUT OF SUBMERGED TUBE TUNNELS. GREAT ADVANCES HAVE BEEN MADE IN THE FIELD OF DISTANCE MEASUREMENT BY ELECTRONIC MEASURING INSTRUMENTS, GEODOMETER AND TELLUROMETER. THESE INSTRUMENTS ARE BASED ON THE MEASUREMENT OF DISTANCE BY MEANS OF MODULATED MICROWAVES. THE FIRST USES LIGHT AS ITS MEDIA, AND THE SECOND RADIO WAVES. THE MEKOMETER WAS DEVELOPED BY THE NATIONAL PHYSICAL LABORATORY USING ELLIPTICALLY POLARIZED LIGHT MODULATION AT MICROWAVE FREQUENCY, AND THE REFLECTED LIGHT IS COMPARED IN PHASE WITH THE EMITTED LIGHT. THIS INSTRUMENT IS PORTABLE AND AUTOMATICALLY CORRECTS ITSELF FOR SMALL CHANGES IN ATMOSPHERIC PRESSURE, AND THE OPERATION IS INDEPENDENT OF HUMIDITY. THE PRECISION INDICATOR OF THE MERIDIAN (PIM) IS DESCRIBED AND ITS USE UNDERGROUND DISCUSSED. COMPUTERIZATION OF MANY OF THE RUN OF THE MILL SURVEY CALCULATIONS SPEEDS THE WORK AND LEADS TO THE PREDICTION THAT AN AUTOMATED SYSTEM OF TUNNEL CONTROL MAY SOON BE DEVELOPED.

  • Availability:
  • Supplemental Notes:
    • Vol 2, No 1, PP 23-28, FIG 12-22, REF 8-15
  • Authors:
    • MCBETH, D G
  • Publication Date: 1970-1

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  • Accession Number: 00235644
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Mar 7 1971 12:00AM