A Dynamic Air Permeameter for Coarse-Textured Soil Columns and Cores J. S. Tyner,* W. C. Wright, J. Lee, and A. D. Crenshaw

Reproduced from Vadose Zone Journal. Published by Soil Science Society of America. All copyrights reserved.

ABSTRACT

umn, the method cannot easily be applied to intact soil cores. These methods and others also cannot distinguish layering within a soil column but rather provide the average value of permeability and water content of an entire sample (Roseberg and McCoy, 1990; Samingan et al., 2003; Rodeck et al., 1994). We developed a new method that does not require an assumption of homogeneity, can be applied to intact soil cores, is fully automated, and can be performed in approximately 1 to 2 d for coarse-textured soils. The method was applied to a single-layer hand-packed soil column, a two-layer hand-packed soil column, and an intact soil core.

The objective of this research was to develop a rapid method to measure the air permeability of multiple layers of a coarse-textured soil column or core. The method required dry air to be pumped through an initially wet soil column, which evaporated the water from the soil within 24 to 48 h. During the drying process, the airflow rate was recorded, and the air pressure was measured at multiple locations along the length of the column. Concurrently, a ␥-ray system was employed to collect water content and dry bulk density measurements. The air permeability as a function of water content was then calculated for each measured interval along the length of the soil column. The method was applied to a hand-packed soil sample intended to be as homogenous as possible, and it was shown that small variations in bulk density contributed to measurable variation in the resulting air permeability. A two-layer, hand-packed soil sample was similarly tested, and the method clearly identified the air permeability of both layers. The method was also successfully performed on an intact heterogeneous field sample collected in a brass sampling tube. Measured air permeabilities from the three tests ranged from 9.8 ⫻ 10⫺13 to 2.1 ⫻ 10⫺10 m2. The method is not appropriate for fine-textured soils or those that shrink significantly when dried.

METHODS AND MATERIALS Air Permeability Theory If the airflow rate through a soil is relatively low, the Klinkenberg (1946) effect describing gas slippage at the grain boundary can be ignored. Under these conditions, Darcy’s Law applies, which enables air permeability (ka) (L2) to be described by

T

he air permeability of soil is commonly measured to enable prediction of airflow and also as an indicator of other soil properties such as hydraulic conductivity (Loll and Moldrup, 1999; Poulsen et al., 2001), soil compaction (Phillips and Kirkham, 1962), gas diffusivity (Moldrup et al., 2001), and spatial variability (Iversen et al., 2003). Small field permeameters have been developed that apply air pressure to a small area of exposed soil while measuring either the airflow rate or decay of inlet pressure over time (Davis et al., 1994; Iversen et al., 2001). These systems can quickly collect air permeability measurements in situ but are limited to sampling outcrops at the ambient water content. Laboratory methods often measure the air permeability of an intact soil core or hand-packed soil column over a range of water contents (Eischens and Swanson, 1996; McKenzie and Dexter, 1996). Springer et al. (1998) and Dane et al. (1998) provide a method to decrease the time required to modify the water content between individual air permeability measurements by applying tension to the entire length of a hand-packed ceramic column. The ceramic column increases the cross-sectional area of water flow into or out of the column, and it reduces the distance water must travel within the column to achieve equilibrium. Because hydraulic connectivity must be achieved between the soil and the ceramic col-

ka ⫽

␮vis Q ⌬L A ⌬P

[1]

where ␮vis is air dynamic viscosity (M L⫺1 T⫺1), Q is volumetric airflow rate (L3 T⫺1), A is the cross-sectional column area (L2), ⌬L is the sample length (L), and ⌬P is the differential pressure (M L⫺1 T⫺2) across ⌬L. Jalbert and Dane (2003) showed that changes in air temperature and relative humidity likely to result from air permeability testing produce less than 1% variability in ␮vis, and therefore, environmental changes within a soil column may be neglected. For traditional air permeability column tests, ⌬L is defined as the length of the column, and ⌬P is defined as the differential pressure between the inlet and outlet.

Air Permeability Hardware For the new method, hypodermic needles are inserted at multiple locations along the length of a soil column (Fig. 1). Plastic tubing connects each hypodermic needle to a pressure transducer (PX170, Omega, Stanford, CT), which enables measurement of ⌬P across each ⌬L. A small air pump forces air through a column of desiccant, which maintains a low inlet relative humidity (RHin). The dry airstream enters the soil column and evaporates the water from an initially wet soil. The RHin and the outlet relative humidity (RHout) are measured with electronic relative humidity sensors (HIH, Honeywell, Morristown, NJ). An electronic airflow rate sensor (FMA3100, Omega, Stanford, CT) measures Q passing through the column. The output signal of both relative humidity sensors, the Q sensor, and the ⌬P sensors are recorded with a datalogger (21X, Campbell Scientific Inc., Logan, UT). The Q and ⌬P data

Biosyst. Eng. and Environ. Sci., The Univ. of Tennessee, 2506 E. J. Chapman Drive, Knoxville, TN 37996. Received 21 June 2004. Original Research Paper. *Corresponding author ([email protected]). Published in Vadose Zone Journal 4:428–433 (2005). doi:10.2136/vzj2004.0092 © Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA

Abbreviations: ka, dry air permeability; Q, volumetric airflow rate; RHin, inlet relative humidity; RHout, outlet relative humidity; ⌬L, sample length; ⌬P, differential pressure; ␪, volumetric water content; ␳db, dry bulk density.

428

429

Reproduced from Vadose Zone Journal. Published by Soil Science Society of America. All copyrights reserved.

www.vadosezonejournal.org

Fig. 1. Schematic of apparatus to measure and log over time differential pressure (⌬P ), volumetric airflow rate (Q ), inlet relative humidity (RHin), and outlet relative humidity (RHout).

are entered in Eq. [1] to calculate ka for each ⌬L interval over time as the soil sample dries.

Water Content and Dry Bulk Density Hardware The volumetric water content (␪) (dimensionless) and dry bulk density (␳db) (M L⫺3) are measured with a custom-built ␥-ray attenuation system. A 4.4-mm-diam. by 10-mm-long 8.9-GBq Am241 source (PO8, Isotope Products Laboratories, Valencia, CA) is centrally located in the end of a 25.4-mm-diam. tungsten rod (Fig. 2). Source collimation is provided by a 3-mmdiam. hole in the end of the tungsten rod. Detector collimation is accomplished by a 6-mm-diam. hole drilled through a lead brick, which is placed 140 mm from the Am241 source. Ideally, collimation would create a ␥-ray beam path that is perfectly one-dimensional. In practice, we have found that our system, with a solid angle of approximately 4 ⫻ 10⫺3 steradians, is sufficient to accurately analyze soil water content. Gamma rays are sensed with a NaI(TI) detector and photomultiplier tube (3m3/3, Bicron, Newbury, OH) in conjunction with a computer-controlled multichannel analyzer (MCA) (MCA 2100R, Princeton Gamma-Tech, Oak Ridge, TN). The MCA is operated with a Visual Basic program provided by the manufacturer (PGT, 2000). With a 37-mm-diam. soil column encased in a clear PVC pipe, approximately 104 counts per sec-

ond is achievable, which enables measurement of ␪ with a probable error of approximately (0.005/␪) ⫻ 100% within 10 s of counting time (Oostrom et al., 1998). A counting rate of 103 counts per second is typical for a 51-mm-diam. soil core collected in a brass sampling tube. To enable measurements of ␪ and ␳db at multiple locations, the soil column is mounted to a computer-controlled linear actuator (BiSlide 15 inch, MN-0150-E01-21, Velmex, Bloomfield, NY) with stepping motor (AMS23-150-2, Advanced Micro Systems, Fairfield, NJ), microstepping driver (DR-4M, Advanced Micro Systems), and PC bus step motor controller (PCMC, Advanced Micro Systems). A code was written to integrate the software controlling the linear actuator and the ␥-ray counting system.

Gamma Ray Attenuation Theory Transmission of a monoenergetic beam of collimated photons through partially saturated porous media can be described by the Lambert–Beer equation (Oostrom et al., 2002)

Io ⫽ I∞ exp(⫺␮axa␳a ⫺ ␮w xw ␳w ⫺ ␮s xs ␳s ⫺ ␮cxc ␳c)

[2]

T ⫺1 )

where I∞ (counts is the count rate with no sample present, Io (counts T⫺1) is the count rate with the sample in place, ␮ (L2 M⫺1) is the mass attenuation coefficient, x (L) is the length of the specific material, ␳ (M L⫺3) is the density (not bulk density) of the specific material, and the subscripts a, w, s, and c represent the air, water, soil, and container components, respectively. The change in volumetric water content (⌬␪) can be calculated from



冒冣

ln Io1 Io2 ⌬␪ ⫽

Fig. 2. Schematic of apparatus to measure volumetric water content (␪) and dry bulk density (␳db) as a function of location and time. For clarity, the airflow system is not shown.

␮w ␳wD

[3]

where Io1 and Io2 are the count rates before and after a change in water content and D (L) is the diameter of the soil column. The ␮w is an experimentally defined parameter, which should not vary if the system is well collimated and the system geometry does not change. We measured a ␮w ⫽ 20.1 mm2 g ⫺1 for our system, with a coefficient of determination (R2) of 0.9999. The

430

VADOSE ZONE J., VOL. 4, MAY 2005

Reproduced from Vadose Zone Journal. Published by Soil Science Society of America. All copyrights reserved.

theoretical value for ␮w from an Am241 source is 20.522 mm2 g⫺1 (Ferraz and Mansell, 1979). The close agreement observed between the measured and theoretical values of ␮w along with the R2 near unity are indicative of proper beam geometry. Because the soil begins wet and the test runs until the soil is completely dry, the initial water content is calculated from

␪initial ⫽ ⫺

end

兺 ⌬␪

⌬ t⫽1

[4]

The ␳db at each sampling location along the length of the column can also be determined by comparing the count rates of the dry soil column to the count rates with only the empty container in the beam path using



冒冣

ln Ic Id ␳db ⫽

␮s D

[5]

where Id is the count rate following permeability testing when the soil is fully dry and Ic is the count rate with only the empty container is in place. The ␮s is calculated from



冒冣

␮s ⫽ ln Ic Id



D ␳db

[6]

where the horizontal bars represent the mean value calculated from all sampling locations. D can be measured directly, and ␳db can be determined by measuring the dry mass of soil and the soil column volume following permeability testing. Alternatively, ␮s can be measured following methods described by Oostrom and Dane (1990), which is necessary if the mineralogy is heterogeneous along the length of the column.

Fig. 3. Volumetric water content (␪) as a function of time for each of the five measured intervals from the single-layer hand-packed soil column. Air enters on the left side and exits on the right.

air pump, and datalogger were started. Initially, RHout quickly approached 100%. When the value of RHout dropped to the value of RHin, the soil column was dry, and air permeability testing was complete. The ka(␪) for intervals between each set of hypodermic needles was calculated by applying Eq. [1]. Following the air permeability testing, the ␳db was calculated from the dry soil mass and the column volume. The empty column was then repositioned on the linear actuator, and Ic was recorded at each of the same locations as during the air permeability testing. The last set of count rates during air permeability testing (Id), in conjunction with Ic, D, ␳s, ␳db, and Eq. [5] and [6] enabled calculation of ␳db at each sampling location.

Laboratory Procedures The water content of soil columns packed in PVC pipe or soil cores collected in brass sampling tubes can be measured by ␥-ray attenuation with an Am241 source. The soil columns were saturated and allowed to drain under gravity in a vertical orientation until water leakage from the column stopped. They were then placed in a horizontal orientation for 24 h to allow for the water to redistribute. Since ␪ and ⌬P were measured at multiple locations, it was not necessary that the water content reach complete equilibrium before testing. Small holes were drilled into the side of each column at the desired air pressure measurement locations before soil core collection or packing to minimize disturbance. Eighteen-gauge hypodermic needles were inserted perpendicular to the length of the column so that the tips of the needles were located near the center of the soil column. Before inserting the needles, the needle tips were folded back to restrict soil from entering the needle shaft. Following insertion, a small amount of air was blown through the needles to ensure they were not clogged. The gap between the needles and the sampling tube was sealed with epoxy or hot glue. Because hot glue is simple to remove, it is recommended if the hardware will be used again. A small amount of very coarse media (1.5-mm-diam. plastic beads) was placed into the column endcaps, which were attached to the ends of the soil column and sealed. Since the air permeability was calculated between each set of needles within the soil column, knowledge of the head loss from the tubing, desiccant column, inlets, outlets, etc., was not required. The ␥-ray attenuation system was programmed to sample approximately every 10 mm along the length of the soil column, while avoiding the needles, for the duration of the air permeability test. Upon initiation of testing, the ␥-ray system,

Soil Core Collection and Preparation Three soil samples were tested using the new air permeameter; two were hand-packed, and one was collected from the field intact. The first sample was a coarse sand that was handpacked into a 37-mm-diam. by 152-mm-height clear PVC pipe. Soil packing was accomplished by placing 10-mm lifts of soil, tamping the soil with a 15-mm-diam. steel rod, disturbing the upper 15 mm of soil, and repeating until the column was full. Effort was made to pack the soil column as uniformly as possible. Hypodermic needles were placed at each end of the column and at 30.5-mm intervals, thus dividing the column into five permeability measurement intervals (Fig. 1). The ␪ were measured at two positions between each pair of needles. The second sample was similarly hand-packed with two layers of soil: 84 mm of well-graded coarse sand followed by 68 mm of poorly graded fine sand. Therefore, the first two sampling intervals (⌬L1 and ⌬L2) were packed with the coarse sand, the last two sampling intervals (⌬L4 and ⌬L5) were packed with the fine sand, and the central sampling interval (⌬L3) was packed with three-fourths coarse sand and one-fourth fine sand. Effort was made to pack each of the two layers of soil homogenously. An intact soil core was collected from a sandy bank of the Tennessee River in Knoxville, TN, using a hand-operated drive sampler with a 51-mm-diam. by 152-mm-height brass sampling tube. The core consisted of thinly bedded layers ranging in size from very fine sand to coarse sand. Thin layers of dark staining, apparently from organic material, were also noted. Based on visual observations, each ⌬L interval consisted of multiple thin heterogeneous layers.

Reproduced from Vadose Zone Journal. Published by Soil Science Society of America. All copyrights reserved.

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Fig. 4. Volumetric airflow rate (Q ), differential pressure (⌬P ), inlet relative humidity (RHin), and outlet relative humidity (RHout) as a function of time for each of the five measured intervals from the single-layer hand-packed soil column.

RESULTS AND DISCUSSION Single-Layer Hand-Packed Soil Column The mean ␪ of the sampling locations within each ⌬L interval as a function of time is presented in Fig. 3. Interval 1 (⌬L1 in Fig. 1) was at the air inlet end of the column, and Interval 5 was at the air outlet. The beginning of the test was marked by applying air pressure to the inlet, which caused water to be displaced from the largest filled pores near the inlet. The displaced water moved toward the outlet where the air pressure was lower. This rapid liquid phase movement of water occurred during the first ␥-ray scan (0–180 s) and is responsible for the early slope of the ␪ profile. During each subsequent 8-h period, the amount of water removed from the core by evaporation increased as the airflow rate increased. The values of Q, ⌬P1 through ⌬P5, RHin, and RHout as a function of time are presented in Fig. 4. The abrupt jumps in pressure and Q at 2.5, 19, and 43 h were due to manually increasing the airflow rate, so the test would progress more quickly. The largest pressure drop for the majority of the test was shown by ⌬P5 because it consis-

Fig. 5. Air permeability (ka) as a function of volumetric water content (␪) for each of the five measured intervals from the single-layer hand-packed soil column.

431

Fig. 6. Dry bulk density (␳db) of the single-layer hand-packed soil column.

tently had the highest ␪. Throughout the test, ⌬P1 and ⌬P2 remained relatively constant, which is to say that the increase in permeability due to decreasing ␪ was largely offset by the increasing Q. Inlet relative humidity remained close to 1.5% until near the end of the test, at which point the desiccant began to expire. Outlet relative humidity remained close to 100% for 27 h but then began to drop rapidly. The end of the test was marked by RHout approaching the value of RHin. Measured data were substituted into Eq. [1] to calculate ka as a function of ␪ (Fig. 5). Close examination of the data from Interval 5 reveals that the permeability decreased initially as ␪ increased and then reversed course as Interval 5 began to dry. Permeability values ranged from 6.1 ⫻ 10⫺12 to 1.7 ⫻ 10⫺10 m2. Although the five curves are similar, closer agreement was expected since effort was made to pack the soil column homogenously. No trend between the magnitude of the ka curves and the position of the ka interval is apparent. Two ␳db measurements were collected from each interval (Fig. 6). Although an attempt was made to pack the column homogeneously, variability of ␳db existed within the column. Given that the differences in density are due solely to packing, a large ␳db should generally be associated with a small ka. Additionally, since the apparent ka of two layers in series is dominated by the smaller ka, the largest ␳db within each interval should dominate the value of the measured ka. Figure 7 presents the dry ka as a function of the largest ␳db measurement from each interval. The value of ␳db predicts 83% of the variation of dry ka. Following the air permeability test and before removal of soil from the PVC column, we measured ⌬P as a function of Q for each interval (Fig. 8). The maximum value of Q was similar to those from the air permeability testing. Linear trend lines were fit through the data collected within each interval. The minimum R2 was 0.999, which indicates that Eq. [1] is valid for the range of Q experienced by the soil column during air permeability testing and that the Klinkenberg effect did not influence the results.

Reproduced from Vadose Zone Journal. Published by Soil Science Society of America. All copyrights reserved.

432

VADOSE ZONE J., VOL. 4, MAY 2005

Fig. 7. Dry air permeability (ka) as a function of dry bulk density (␳db) from the single-layer hand-packed soil column. Each data point represents the most dense ␳db measurement collected within each air permeability interval.

Two-Layer Hand-Packed Soil Column The ka versus ␪ curves from the two-layer hand-packed soil column are presented in Fig. 9. Permeabilities ranged from 2.4 ⫻ 10⫺12 to 2.1 ⫻ 10⫺10 m2. The two ka curves from the coarse sand (Intervals 1 and 2) are similar, and the ka curves from fine sand (Intervals 4 and 5) are also similar. Interval 3 showed characteristics of both soil types; it had the convex shape of the coarse sand but had a maximum ka characteristic of the fine sand. The small maximum ka for Interval 3 is sensible since the apparent permeability of two layers of soil in series is dominated by the contribution of the less permeable layer. A benefit of this new method is that it can distinguish layering that would otherwise be missed by methods that measure the ⌬P and ␪ across the entire length of a soil column.

Intact Field-Collected Soil Core Results from the air permeability test of the intact core are presented in Fig. 10. Permeabilities ranged from 9.8 ⫻ 10⫺13 to 5.0 ⫻ 10⫺11 m2 and were approximately

Fig. 8. Differential pressure (⌬P ) as a function of volumetric airflow rate (Q ) for each of the five measured intervals from the singlelayer hand-packed soil column. The smallest R2 was 0.999, which indicates that Eq. [1] was valid for the range of Q applied during permeability testing.

Fig. 9. Dry air permeability (ka) as a function of volumetric water content (␪) for each of the five measured intervals from a twolayer hand-packed soil column.

linear across the full range of ␪, from 0.42 to 0. The pressure sensor for Location 2 failed during the test, so only the first portion of the data stream was collected and plotted. No trend between the magnitude of the ka curves and the position of the ka interval is apparent. This test demonstrates the ability of this method to measure ka curves of multiple layers of an intact field soil core collected in a standard brass sampling tube. Soil cores are commonly collected in brass tubes during environmental investigations and during monitoring well installations, so the ability to measure the air permeability of this type of soil core is significant. Like most air permeameters, this new method is susceptible to leakage of air between the soil and the container if the soil shrinks when dried. When packed soil columns are tested, clear PVC should be utilized to enable visual examination of shrinkage. Additionally, this method is only appropriate for coarse-textured soils since sufficient airflow must be present at the initiation of testing to dry out the soil within a reasonable time span.

CONCLUSIONS A new method to measure the air permeability of a soil column or core was presented. Instead of obtaining

Fig. 10. Dry air permeability (ka) as a function of volumetric water content (␪) for each of the five measured intervals from an intact soil core. The pressure sensor for Interval 2 failed during testing.

Reproduced from Vadose Zone Journal. Published by Soil Science Society of America. All copyrights reserved.

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an average permeability value for an entire soil column, the method provides permeability measurements for multiple distinct intervals within a soil column. Testing is automated and requires a duration of approximately 24 to 48 h for coarse-textured soils. This method is not appropriate for fine-textured soils because sufficient airflow is required to remove water from the soil column within a reasonable time period. Also, fine-textured soils are likely to shrink as they dry, causing leakage of air between the soil and the tube. Results from a homogenous handpacked soil column were presented, and it appears that small variations in bulk density caused noticeable differences in permeability. A two-layer hand-packed soil column was tested, and the resultant permeability curves from the two layers were distinctly identifiable. The method was also completed on an intact soil core collected within a 51-mm-diam. by 152-mm-height brass sampling tube, which demonstrates the ability of the method to be performed on commonly collected soil cores. REFERENCES Dane, J.H., C. Hofstee, and A.T. Corey. 1998. Simultaneous measurement of capillary pressure, saturation, and effective permeability of immiscible liquids in porous media. Water Resour. Res. 34(12): 3687–3692. Davis, J.M., J.L. Wilson, and F.M. Phillips. 1994. A portable air-minipermeameter for rapid in situ field measurements. Ground Water 32(2):258–266. Eischens, G., and A. Swanson. 1996. Proposed standard test method for measurement of pneumatic permeability of partially saturated porous materials by flowing air. Geotech. Test. J. 19(2):232–239. Ferraz, E.S.B., and R.S. Mansell. 1979. Determining water content and bulk density of soil by gamma ray attenuation methods. Tech. Bull. 807. Univ. of Florida, Gainesville. Iversen, B.V., P. Moldrup, P. Schjønning, and O.H. Jacobsen. 2003. Field application of a portable air permeameter to characterize spatial variability in air and water permeability. Vadose Zone J. 2: 618–626. Iversen, B.V., P. Schjønning, T.G. Poulsen, and P. Moldrup. 2001. In situ, on-site and laboratory measurements of soil air permeability:

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Boundary conditions and measurement scale. Soil Sci. 166(2): 97–106. Jalbert, M., and J.H. Dane. 2003. A handheld device for intrusive and nonintrusive field measurements of air permeability. Vadose Zone J. 2:611–617. Klinkenberg, L.J. 1946. The permeability of porous media to liquids and gases. p. 200–213. In American Petroleum Institute drilling and production practice. Am. Petroleum Inst., Washington, DC. Loll, P., and P. Moldrup. 1999. Predicting saturated hydraulic conductivity from air permeability: Application in stochastic water infiltration modeling. Water Resour. Res. 35(8):2387–2400. McKenzie, B.M., and A.R. Dexter. 1996. Methods for studying the permeability of individual soil aggregates. J. Agric. Eng. Res. 65(1): 23–28. Moldrup, P., T. Olesen, T. Komatsu, P. Schjønning, and D.E. Rolston. 2001. Tortuosity, diffusivity, and permeability in the soil liquid and gaseous phases. Soil Sci. Soc. Am. J. 65(3):613–623. Oostrom, M., and J.H. Dane. 1990. Calibration and automation of a dual-energy gamma system for applications in soil science. Agron. and Soils Dep. Ser. 145. Alabama Agric. Exp. Stn., Auburn Univ., Auburn, AL. Oostrom, M., J.H. Dane, and R.J. Lenhard. 2002. Fluid contents. p. 1539–1563. In J.H. Dane and G.C. Topp (ed.) Methods of soil analysis. Part 4. Physical methods. SSSA Book Ser. 5. SSSA, Madison, WI. Oostrom, M., C. Hofstee, J.H. Dane, and R.J. Lenhard. 1998. Singlesource gamma radiation procedures for improved calibration and measurements in porous media. Soil Sci. 163(8):646–656. PGT. 2000. Quantum-MCA. Ver. 4.04.00. PGT Inc., Princeton, NJ. Phillips, R.E., and D. Kirkham. 1962. Soil compaction in the field and corn growth. Agron. J. 54:29–34. Poulsen, T.G., B.V. Iversen, T. Yamaguchi, P. Moldrup, and P. Schjønning. 2001. Spatial and temporal dynamics of air permeability in a constructed field. Soil Sci. 166(3):153–162. Rodeck, S.A., B.A. DeVantier, and B.M. Das. 1994. Air-permeability measurement for soil at low and high pressure. J. Environ. Eng. 120(5):1337–1345. Roseberg, R.J., and E.L. McCoy. 1990. Measurement of soil macropore air permeability. Soil Sci. Soc. Am. J. 54(4):969–974. Samingan, A.S., E. Leong, and H. Rahardjo. 2003. A flexible wall permeameter for measurement of water and air coefficients of permeability of residual soils. Can. Geotech. J. 40(3):559–574. Springer, D.S., H.A. Loaiciga, S.J. Cullen, and L.G. Everett. 1998. Air permeability of porous materials under controlled laboratory conditions. Ground Water 36(4):558–565.

A Dynamic Air Permeameter for Coarse-Textured Soil ...

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