Abstract:
RESULTS OF PERMEABILITY TESTS ON VARIOUS MATERIALS WITH APPROPRIATE APPARATUS SHOW THE IMPORTANCE OF DETAILED SPECIFICATIONS OF PROCEDURE AND MATERIALS AND THE EXTREMELY WIDE RANGE OF POSSIBLE VALUES. FOR INSTANCE, THE PERMEABILITY OF A MATERIAL DEPENDS ON THE METHOD OF ITS COMPACTION, DENSITY, GRADATION AND PLASTICITY. SUBSTITUTION OF TEST RESULTS IN APPROPRIATE FORMULAS ILLUSTRATES THE EFFECT OF BOUNDARY CONDITIONS AND THE COEFFICIENT OF PERMEABILITY ON THE RATE OF DRAINAGE. THE SMALL GRADIENTS AVAILABLE FOR LATERAL DRAINAGE OF BASE COURSES PREVENT RAPID DRAINAGE OF DENSE-GRADED MATERIALS ON IMPERVIOUS SUBGRADES. EVEN AFTER DRAINAGE A DENSE-GRADED MATERIAL WILL HOLD CONSIDERABLE WATER BY CAPILLARITY IF PROTECTED FROM EVAPORATION. WHILE OPEN-GRADED MATERIALS WILL DRAIN MORE READILY, PROVISION MUST BE MADE TO PREVENT INTRUSION OF FINE SUBGRADE SOIL, AND IT IS DIFFICULT TO COMPACT THEM SO THAT TRAFFIC WILL NOT CAUSE FURTHER DISPLACEMENT. SINCE BOTH DENSITY AND DRAINABILITY ARE DESIRABLE, THE RANGE OF SATISFACTORY MATERIALS IS LIMITED, AND IT IS SOMETIMES NECESSARY TO CHOOSE WHICH PROPERTY SHOULD BE GIVEN PREFERENCE. /AUTHOR/
Supplemental Notes:
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