CLOSURE ON AIR PERMEABILITY OF COMPACTED COHESIVE SOILS

DISCUSSERS MATYAS AND SATYANARAYANA QUESTION THE USE OF THE TERM "ESSENTIALLY ZERO" WHEN REFERRING TO THE AIR PERMEABILITY AT OPTIMUM WATER CONTENT AND BEYOND. IT WAS RECOGNIZED THAT A FINITE PERMEABILITY DID EXIST IN SOME CASES; HOWEVER, SINCE THE PERMEABILITY CHANGES BY A FACTOR OF 100 OR MORE AT ABOUT OPTIMUM, IT WAS CONSIDERED THAT THE ADVERB "ESSENTIALLY" COULD BE APPROPRIATELY APPLIED TO "ZERO" TO SUITABLY DESCRIBE THE PERMEABILITY. THE WRITERS AGREE THAT A MORE GENERAL CONCLUSION WOULD BE THAT THE MAJORITY OF THE TEST RESULTS INDICATE THE AIR PERMEABILITY IS ZERO AT MOISTURE CONTENTS WET OF OPTIMUM. THE RESULTS OF MATYAS' TESTS ON GLACIAL TILL WERE PERFORMED IN A TRIAXIAL CELL WHICH ALLOWS SOME EXPANSION OF THE SAMPLE AFTER COMPACTION AND ALSO THE POSSIBILITY OF AN AIR CHANNEL AT THE BOUNDARY OF THE SOIL. HE STATED THAT THE AIR PERMEABILITY VALUES AT LOW CONFINING PRESSURES MIGHT BE SLIGHTLY LARGE OWING TO SOME FREE MOVEMENT OF AIR BETWEEN THE MEMBRANE AND THE SOIL SPECIMEN. IT IS IMPORTANT THAT ABSOLUTELY NO BOUNDARY LEAKAGE OCCURS IF CORRECT VALUES OF PERMEABILITY ARE TO BE OBTAINED. SATYANARAYANA INDICATES THAT MAXIMUM UNCONFINED COMPRESSION STRENGTH OCCURS ON THE WET SIDE OF OPTIMUM MOISTURE CONTENT FOR A SAND-CLAY MIXTURE DOMINANT IN CLAY. HOWEVER, THE TESTS WERE ALL CONDUCTED ON A SOIL CEMENT AND ARE NOT REALLY APPLICABLE TO COMPACTED SOIL. DATA BY TURNBULL AND FOSTER ON A LEAN CLAY INDICATES THAT STRENGTH, AS MEASURED BY THE CBR TEST, OPTIMIZES ON THE DRY SIDE OF THE OPTIMUM WATER CONTENT. THE USE OF THE BISHOP EFFECTIVE STRESS WAS SUGGESTED BY SATYANARAYANA TO EXPLAIN A DECREASE IN SHEAR STRENGTH WET OF OPTIMUM. HOWEVER, ONCE THE AIR PERMEABILITY BECOMES "ESSENTIALLY ZERO," THE WRITERS DOUBT THAT THE PORE AIR PRESSURE WILL INCREASE PROPORTIONALLY WITH MOISTURE CONTENT. OTHER AUTHORITIES ARE QUOTED WHICH SUPPORT THIS VIEW. REPORTS ISSUED: AIR PERMEABILITY OF COMPACTED COHESIVE SOILS, LEONARD J. LANGFELDER, C.F. CHEN, JOHN A. JUSTICE, ASCE PROC. PAPER 6040, JULY 1968.

  • Supplemental Notes:
    • Vol 96, No SM 1, PP 303-5, 28 REF, 1 APP
  • Authors:
    • Langfelder, L J
    • Chen, C F
    • Justice, J A
  • Publication Date: 0

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  • Accession Number: 00232810
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Mar 25 1970 12:00AM