SHEAR STRENGTH OF SOME HAWAIIAN LATOSOLS

LATOSOLS ARE AMONG THE MOST ENIGMATIC SOILS, BECAUSE OF THE PAUCITY OF ENGINEERING STUDIES AND THE FAILURE OF LABORATORY TESTS TO ACCURATELY PREDICT FIELD BEHAVIOR. SOME IN SITU SHEAR STRENGTH DATA ARE PRESENTED ON HAWAIIAN LATOSOLS AND THE DATA COMPARED WITH ENGINEERING CLASSIFICATION AND CLAY MINERALOGY TO ATTEMPT TO RELATE WITH ENVIRONMENTAL FACTORS, IN PARTICULAR THE MEAN ANNUAL PRECIPITATION. IN SITU-BORE-HOLE SHEAR TESTS AT 2 TO 3 FT. DEPTH IN HAWAIIAN LATOSOLS INDICATE A LOW COHESION, USUALLY 0.5 TO 0.9 PSI, AVERAGING ABOUT 0.6 PSI, AND AN ANGLE OF INTERNAL FRICTION USUALLY 20 TO 30 DEGREES, AVERAGING ABOUT 25 DEGREES. TWO TESTS AT THE 3.5 FT. DEPTH GAVE ABOUT THE SAME ANGLE OF INTERNAL FRICTION, BUT AN APPRECIABLY HIGHER COHESION. COHESION AND INTERNAL FRICTION APPEARED TO VARY SYMMETRICALLY WITH RAINFALL. THE KAOLINITE CONTENT DETERMINED FROM X-RAY DIFFRACTION VARIED FROM ABOUT 10 TO 35%, BEING LOWER WITH MORE RAINFALL. GIBBSITE AND GOETHITE CONTENTS INCREASED WITH INCREASING RAINFALL IN THE RANGE OF 30 TO 90 INCHES PER YEAR. A POSITIVE CORRELATION WAS FOUND BETWEEN KAOLINITE CONTENT FROM X-RAY DIFFRACTION AND COHESION FROM THE BORE-HOLE SHEAR TEST. BY ASSUMING SATURATION AND SEEPAGE AND USING AVERAGE VALUES FOR COHESION, ANGLE OF INTERNAL FRICTION, SOIL UNIT WEIGHT AND SLOPE ANGLE, THE CALCULATED DEPTH TO FAILURE ON AN INFINITE SLOPE IS 1.9 FEET. AT ORDINARY MOISTURE CONTENTS, CALCULATIONS INDICATE THE SLOPES ARE STABLE, AGREEING WITH WENTWORTH'S OBSERVATION THAT SLIDES OCCURED AFTER UNUSUALLY HEAVY RAINS. THE INCREASE IN COHESION WITH DEPTH PRECLUDES DEEP SOIL SLIDES AND IS AN ARGUMENT FOR PARALLEL SLOPE RETREAT AS A RESULT OF WEATHERING.

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Filing Info

  • Accession Number: 00235394
  • Record Type: Publication
  • Report/Paper Numbers: pp 80-84
  • Files: TRIS
  • Created Date: May 5 1994 12:00AM