THE EFFECTS OF SURFACE ROUGHNESS ON THE SHEAR STRENGTH OF JOINTS IN ROCK

FLAT SURFACES IN BASALT, DOLOMITE, LIMESTONE, SANDSTONE, SILTSTONE, GRANITE, AND SCHISTOSE GNEISS, PREPARED BY LAPPING WITH FINE #600 GRIT, BY LAPPING WITH COARSE #80 GRIT, AND BY SANDBLASTING, HAVE BEEN SHEARED WET AND DRY UNDER NORMAL PRESSURES FROM 10 TO 1000 PSI TO DETERMINE THE MANNER IN WHICH SURFACE PREPARATION AFFECTS THE FRICTIONAL COMPONENT OF SHEAR STRENGTH. TO SUPPLEMENT TEST DATA FROM THE FLAT SURFACES, TESTS WERE ALSO PERFORMED ON NATURAL JOINTS IN GRANITE AND SILTSTONE, ON JOINTS IN GRANITE GROUTED WITH NEAT CEMENT, AND ALONG INTACT BEDDING IN TWO SHALES. IN ALL, APPROXIMATELY 1000 SHEAR TESTS WERE PERFORMED USING A HIGH-CAPACITY DIRECT-SHEAR MACHINE DESIGNED SPECIFICALLY FOR THIS TESTING PROGRAM. INITIAL AND RESIDUAL ANGLES OF SLIDING FRICTION FOR THE FLAT SURFACES RANGED FROM 19 TO 40 DEGREES, WITH THE BULK OF THE DATA FALLING BETWEEN 26 AND 36 DEGREES. SURFACE PREPARATION HAD A DEFINITE EFFECT ON SHEAR STRENGTH. THERE WAS AN INCREASE IN INITIAL SHEAR STRENGTH WITH THE INCREASE IN SURFACE ROUGHNESS FROM THE #600 TO THE #80 SURFACE PREPARATION. THE #80 AND SANDBLASTED SURFACES, HOWEVER, HAD SIMILAR FRICTIONAL CHARACTERISTICS. RESIDUAL STRENGTH WAS ALSO A FUNCTION OF SURFACE ROUGHNESS AT LOW NORMAL PRESSURES, BUT SURFACE DAMAGE TENDED TO NEUTRALIZE THE EFFECT AT HIGHER NORMAL PRESSURES. MINERALOGY AND ROCK TYPE APPEAR TO BE THE CHIEF FACTORS CONTROLLING SHEAR STRENGTH FOR A GIVEN TESTING SITUATION. THE HIGHEST INITIAL AND RESIDUAL STRENGTHS OCCURRED ON LIMESTONE, THE LOWEST ON THE MICA-RICH SCHISTOSE GNEISS. FOR TESTS ON THE NATURAL JOINT SURFACES, IRREGULARITIES WITH THE STEEPEST INCLINATION TO THE DIRECTION OF SHEARING WERE RESPONSIBLE FOR THE MOBILIZED GEOMETRICAL COMPONENT OF SHEAR STRENGTH. THE DIRECT SHEAR METHOD OF TESTING SHOULD NOT BE USED FOR INTACT SHALE SPECIMENS, EVEN WHEN THERE ARE WELL DEFINED INCIPIENT FAILURE PLANES. CEMENT GROUTING SHOULD BE USED WITH CAUTION WHEN THE STRENGTH OF THE GROUTED JOINT IS A MAJOR CONSIDERATION. /AUTHOR/

  • Supplemental Notes:
    • 293 Pp, 70 FIG, 32 TAB, 41 PHOT, 65 REF, 3 APP
  • Corporate Authors:

    U.S. Army Corps of Engineers

    ,    
  • Authors:
    • Coulson, J H
  • Publication Date: 1970-10

Subject/Index Terms

Filing Info

  • Accession Number: 00235838
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jan 26 1971 12:00AM