THE GEOLOGY AND ENGINEERING PROPERTIES OF SOUTH AFRICAN CALCRETES. VOL. 2: AGE, PROSPECTING METHODS, AND ENGINEERING TEST METHODS

CALCRETES SELDOM CONTAIN ANY FOSSILS USABLE FROM A DATING POINT OF VIEW, AND ASSOCIATED STONE ARTEFACTS AND RADIOMETRIC METHODS AFFORD THE BEST MEANS OF DATING THESE MATERIALS. CONTRARY TO THE IMPRESSION GAINED BY COMMENTS IN THE LITERATURE, THE RADIOCARBON METHOD HAS BEEN FOUND TO BE A MOST PROMISING MEANS OF DATING CALCRETES. RATES OF CALCRETE FORMATION VARYING BETWEEN 0.001 AND 0.033 INCHES PER YEAR HAVE BEEN CALCULATED FROM THE CALCRETE C-14 DATES FOUND IN THE LITERATURE AND THOSE MENTIONED ABOVE. THE FASTER RATES ARE LIKELY TO BE THE CORRECT ONES. IT WOULD APPEAR THAT CALCRETES IN SOUTHERN AFRICA CAN BE CLASSIFIED INTO THE FOLLOWING AGE GROUPS: PRE-PLIOCENE, PLIOCENE, FIRST INTERMEDIATE, SECOND INTERMEDIATE, AND LATER STONE AGE TO PRESENT DAY. WIDESPREAD PHASES OF CALCIFICATION APPEAR TO HAVE OCCURRED DURING PLIOCENE, FIRST INTERMEDIATE AND SECOND INTERMEDIATE TIMES. IDEAL CONDITIONS FOR CALCRETE FORMATION ARE PROBABLY DURING WANING PLUVIALS RATHER THAN DURING INTERPLUVIALS AS IS COMMONLY SUPPOSED. METHODS OF LOCATING CALCRETE DEPOSITS FOR ROAD CONSTRUCTION ARE DISCUSSED AND IT IS CONCLUDED THAT THE BEST METHOD OF LOCATING BURIED CALCRETE DEPOSITS AT THE PRESENT TIME CONSISTS OF THE COMBINED USE OF AIRPHOTO INTERPRETATION, PLANT INDICATORS, TOPOGRAPHIC SETTING, AND THE RAPID PROBING DEVICE DESCRIBED. CALCRETE DEPOSITS TEND TO BE RATHER VARIABLE IN DEPTH, THICKNESS, LATERAL EXTENT, AND QUALITY. THE APPLICABILITY OF METHODS FOR THE DETERMINATION OF THE ENGINEERING PROPERTIES OF CALCRETES IS EXAMINED IN SOME DETAIL. THE MOST DESIRABLE METHOD FOR THE PREPARATION OF CALCRETE SOIL FINES FOR INDICATOR TESTING APPEARS TO BE A WET METHOD WHICH DOES NOT INVOLVE HEATING AT MORE THAN ABOUT 60C. THE LIQUID LIMIT AND PLASTICITY INDEX TESTS ARE THOUGHT TO YIELD SOMEWHAT ERRATIC RESULTS ON CALCRETES UNLESS CARRIED OUT BY CAREFULLY STANDARDISED METHODS. A LIQUID LIMIT METHOD WHICH PERMITS DRYING AND REWETTING CYCLES TO ADJUST THE MOISTURE CONTENT IS LIKELY TO YIELD SPURIOUSLY HIGH VALUES. BAR LINEAR SHRINKAGE IS THOUGHT TO BE A RELIABLE, PRACTICAL, AND SIMPLE SUBSTITUTE FOR A PLASTICITY INDEX. MECHANICAL ANALYSES ARE LIKELY TO YIELD HIGH OPERATOR VARIABILITIES DUE TO THE USUALLY WEAK BUT VARIABLE CALCRETE PARTICLE STRENGTH. PARTICLE STRENGTH VARIES WITH SIZE FRACTION EVEN WITHIN THE SAME SAMPLE. A SIMPLE NEW FIELD PLIERS TEST FOR AGGREGATE STRENGTH IS DESCRIBED AND CORRELATED WITH THE 10% FINES AGGREGATE CRUSHING TEST. THE PLIERS TEST YIELDS RESULTS WHICH CORRELATE WELL WITH THE PERFORMANCE OF NODULAR CALCRETE GRAVEL ROAD WEARING COURSES. A GOOD CORRELATION HAS BEEN FOUND BETWEEN THE MEANS MOHS HARDNESS (H) OF CALCRETES AND THEIR AGGREGATE CRUSHING STRENGTHS. A NEW, SIMPLE, AND CONVENIENT POCKET MOHS HARDNESS TESTER EMPLOYING METAL BLADES IS DESCRIBED. THE SOIL PASTE CONDUCTIVITY METHOD TOGETHER WITH A QUALITATIVE SULPHATE TEST IS SUGGESTED AS A RAPID INDICATOR TEST FOR THE PRESENCE OF DELETERIOUS SOLUBLE SALTS IN ROAD MATERIALS. IT IS CONSIDERED THAT MORE WEIGHT SHOULD BE ATTACHED TO TESTS OF COMPACTED STRENGTH SUCH AS TEXAS TRIAXIAL OR CALIFORNIA BEARING RATIO RATHER THAN TO INDICATOR TESTS SUCH AS PLASTICITY AND GRADING. /AUTHOR/

  • Supplemental Notes:
    • 294 Pp, FigS, TABS, REFS
  • Corporate Authors:

    Witwatersrand University /S Africa

    /Department of Geology
    ,   United States 
  • Authors:
    • Netterberg, F
  • Publication Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 00230060
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 19 1971 12:00AM