Laserfiche WebLink
k _ alln 1 <br />At h2 <br />Where: <br />k coefficient of permeability, <br />cm/sec <br />a inside cross -sectional area of <br />standpipe, cm2 <br />1 thickness of test specimen, cm <br />A cross -sectional area of <br />specimen, cm2 <br />hi hydraulic head on specimen at <br />time, ti <br />h2 hydraulic head on specimen at <br />time, t2 <br />Figure 2.1. Laboratory Permeameter (Left) and Permeability Calculation (Right) <br />Figure 2.2 shows the graphical relationship between permeability and air voids. As the <br />air voids are increased greater than 9.6%, the permeability increases dramatically. Although the <br />permeability of the mixture with 13% air voids is still much lower than that of permeable bases, <br />it is still approximately six times more permeable than class 5 aggregate base. This relationship <br />was also found by Cooley, Brown and Maghsoodloo (2001) who reported that coarse, dense <br />graded SuperPave mixtures with a nominal maximum aggregate size of 3/4" (19.0 mm) became <br />excessively permeable at approximately 5.5% in -place air voids, which corresponded to a field <br />permeability value of 40.82 in/day. They also observed that permeability appeared to increase <br />exponentially with in -place voids (Figure 2.3). <br />Permeability, in/day <br />30 <br />25 <br />20 <br />15 <br />10 <br />5 <br />0 <br />Permeabilityvs. Density <br />7 9.6 13.3 <br />Air Voids, % <br />Figure 2.2. Permeability vs. Air Voids <br />IMF <br />CL.5 <br />Agg Base <br />B-10 <br />