The Development of a New Air Permeability Testing Apparatus

Abstract

This thesis presents the development of a new laboratory testing apparatus for the measurement of the coefficient of air permeability of soil specimens using steady state methods. The apparatus was designed to measure coefficients of air permeability with in a range of 1*10-5 to 1 * 10-9 cm/s at a standard pressure and temperature of 101.3 kPa and 20°C respectively. The apparatus design allows for duplicate, independent measurements of air volume flow rates and the air pressure differential. The apparatus features the use of a large lucite testing cell which can accommodate specimens up to four inches in diameter and eight inches in height. The apparatus was originally developed to determine the coefficient of air permeability of undisturbed specimens of a highly plastic, fractured clay (i.e., Regina clay). A laboratory testing program was conducted on specimens of a sandy till (i.e., Floral till) to verify the performance of the new air permeability testing apparatus. The apparatus was confirmed to be capable of measuring the coefficient of air permeability of soil specimens with in a range of 8.7*10-6 to 2.6*10-8 cm/s; nearly three orders of magnitude (at standard atmospheric pressure and a temperature of 20°C). The coefficient of air permeability of Floral till was shown to be highly dependent on the degree of saturation of the soil specimens, and dependent to a lesser degree on the void ratio (i.e., density) of the soil. A second laboratory testing program was conducted on undisturbed specimens of Regina clay. The results of the laboratory testing program indicate that the coefficient of air permeability of Regina clay is relatively low; approximately 1*1 0 -7 cm/s near the surface of the deposit and decreases rapidly with depth. The soil matrix of Regina clay is essentially saturated through out the entire depth of the in-situ deposit and is relatively impermeable to the advective flow of air. The advective flow of air through the bulk soil deposit is therefore controlled by the characteristics of the unsaturated fracture network. The fracture network was shown to significantly increase the bulk coefficient of air permeability of Regina clay in the upper two to three meters of the deposit. The influence of the fractures is not as significant at greater depths. This is attributed to the decrease in fracture density and the increase in confining pressure which occurs with increasing depth in the deposit.