DESIGN OF TUNNEL LININGS

WHILE NONCIRCULAR SHAPES FOR TUNNEL LININGS HAVE SOME ADVANTAGES, IF ONE POSTULATES ONE HAVING SOME BENDING STRENGTH IN WHICH THE DESIGN TAKES ACCOUNT OF SHEAR INTERACTIONS BETWEEN LINING AND GROUND, THE NUMBER OF VARIABLES BECOMES LARGE, AND ANALYSIS FOR OTHER THAN A LIMITED NUMBER OF SPECIFIC CASES MAY BE IMPRACTICAL. IN THE PRESENT WORK IT IS ASSUMED THAT LINING AND ITS SURROUNDING ROCK REMAIN ELASTIC, THAT THE INTERACTION BETWEEN THE LINING AND THE GROUND CAN BE REPRESENTED BY A UNIFORM RADIAL PRESSURE, AND THAT THE LINING HAS NO BENDING STIFFNESS TO RESIST ANY VARIATIONS IN RADIAL COMPRESSION IMPOSED UPON IT. THIS REDUCES THE NUMBER OF STATICAL INDETERMINACIES FROM INFINITY TO ONE. WHILE THESE ASSUMPTIONS ARE NOT COMPLETELY UNREALISTIC, A MORE ELABORATE STRESS ANALYSIS, ALLOWING FOR A LARGE BUT FINITE NUMBER OF STATICAL INDETERMINACIES, WOULD BE NEEDED TO CHECK HOW REALISTIC IT IS. THE STRESS ANALYSIS IS FIRST CONSIDERED FOR THE TWO-DIMENSIONAL CASE. A DISTINCTION IS MADE BETWEEN THE MOHR AND COULOMB CRITERIA AND THEIR APPLICABILITY. STRENGTH EQUATIONS ARE SOLVED FOR A GIVEN CASE. IT IS NOTED THAT THE STIFFNESS OF THE LINING CANNOT BE DEFINED BECAUSE THE DEFORMATION OF THE ROCK IS TREATED AS INDETERMINATE; HOWEVER, IT MUST BE SUFFICIENTLY DEFORMABLE TO ALLOW THE ROCK TO MOVE AND MOBILIZE ITSELF INTO A PLASTIC STATE. AS THIS IS NOT ENTIRELY POSSIBLE, THE PRESSURE ON A REAL LINING WILL BE SOMEWHERE INDETERMINATE BETWEEN THE LIMIT STATE AND THE ELASTIC STATE. ROOF LOADING AND THREE KINDS OF LOOSENING ARE DISCUSSED. THE ROLES OF ROCK BOLTS AND INVERTS ARE NOTED BRIEFLY. THE CLEARANCE REQUIREMENTS OF HIGHWAY TUNNELS CALL FOR GREATER WIDTH THAN HEIGHT, AND THE SEARCH FOR AN OPTIMUM LINER SHAPE FOR THESE REQUIREMENTS WOULD ENTAIL A CONSIDERABLE RESEARCH PROGRAM. A FIGURE IS SHOWN THAT REPRESENTS A FIRST CHOICE FOR A SHAPE SUITABLE FOR A SINGLE THREE-LANE HIGHWAY, ALONG WITH THE STRESSES CAUSED BY A SPECIFIC LOADING PATTERN. A SHAPE THAT FITS CLOSELY AROUND THE CLEARANCES MAY BE SUBJECTED TO HIGHER BENDING MOMENTS THAN A TRADITIONAL HORSESHOE, THE COST OF LINER REINFORCEMENT THEN OUTWEIGHING THE SAVING IN EXCAVATION. ANALYSIS SHOWS THAT QUITE LARGE RADII OF CURVATURE OF THE LINING ARE NEVERTHELESS ABLE TO BRING INTO PLAY A PATTERN OF PASSIVE PRESSURE IN THE ROCK, KEEPING BENDING MOMENTS MUCH SMALLER THAN MIGHT HAVE BEEN FEARED.

  • Supplemental Notes:
    • Vol 66, No 782, PP 993 - 998, 10 FIG, 2 TAB, 1 PHOT, 11 REF
  • Authors:
    • Howells, D A
  • Publication Date: 1971-9

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Filing Info

  • Accession Number: 00236261
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Feb 8 1972 12:00AM