EFFECT OF ENTRAPPED AIR UPON THE PERMEABILITY OF SOILS

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Abstract
When soils are wetted for permeability tests an appreciable amt. of air is entrapped within the pores of the soil. This air is slowly but gradually dissolved by the water passing through the soil during the test, and when tests are carried on over a sufficiently long period practically all of this air is removed. The presence of the air in the soil appreciably decreases the permeability of the soil as compared with air-free soil. Most of the soils tested show a significant increase in permeability as the air is eliminated. In some instances permeability rates of more than 30 times the previous minimum rate have resulted with the elimination of the air. The paper describes a number of tests performed which show that it is the elimination of entrapped air in the soil that causes the increase in permeability. These tests include: The detn. of the amt. of air actually entrapped and its correlation with the subsequent relative increase in permeability; the effect of evacuating the dry soil and wetting it in the absence of air; the effect of interrupting a permeability test and admitting air into the soil, and the effect of entrapped air upon the results of tests performed with variable head permeameters.

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