pecific YieldColumn Drainage and 

Centrifuge Moisture Content

GEOLOGICAL SURVEY WATER SUPPLY PAPER 1662-A

'repared in cooperation with the 

California Department of 

Voter Resources
Specific Yield 

Column Drainage and 

Centrifuge Moisture Content

By A.. I. JOHNSON, R. C. PRILL and D. A. MORRIS

HYDROLOGIC PROPERTIES OF EARTH MATERIALS

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1662-A

Prepared in cooperation with the California Department of Water Resources

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, Jr., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

First printing 1963 

Second printing 1992

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government

For sale by the Books and Open-File Reports Section 

U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225
CONTENTS

Page

Abstract________________________________________________________ Al

Introduction._____________________________________________________ 2

Objectives and proposed scope of research program. _______________ 2

Review of previous work_ ______________________________________ 3

Organization of investigation__________________________________ 4

Acknowledgments. _----____-___________-_____-___-_-_____-__-_ 4

Investigation of column drainage____________________________________ 4

Technique._ __________________________________________________ 4

Materials. ________________________________________________ 4

Columns ______________________ _^_ _________________________ 6

Packing._ ________________________________________________ 6

Wetting nuid__________________________________-__-__-_--_ 8

Observation of water level-_________________________________ 8

Cleaning of porous media___---_--_----_----------_---_---_- 9

Methods of wetting._________________________-__-_--__----_ 9

Methods of drainage._____________________-____-_--__---_-- 10

Methods of sampling moisture distribution__________________ 12

Controls employed_--______--____-___--__--_-_---___------- 12

Discussion of drainage data.________________-________--_---__--- 12

Effect of cleaning porous media. ____________________________ 12

Comparison of drainage methods ____________________________ 12

Effect of column diameter__________________________________ 15

Effect of method of wetting.________________________________ 17

Effect of packing rnethod___________________________-------- 20

Characteristics of packer_________.___-_____--___-----_- 22

Effect of vibration on settling.__________________________ 23

Development of packing technique_-________-_---_-_--_ 23

Effect of surcharge______________________--_-__--- 23

Effect of amplitude on porosity______.___-_-__----_ 25

Packing of long columns__________________.,_-_---- 28

Effect of packing on sorting___________________________ 28

Effect of dye on drainage._______________________-__-_-_---- 32

Effect of time on drainage________________________---------- 32

Investigation of centrifuge moisture content__________________________ 35

Technique.-_--___--_._________._________-_____.____---------- 35

Materials.. _ -_-______________________________-__----_----- 35

Procedures. _ _ ______________________-_______-------_-_--- 36

Filter paper_____________________________________________ 38

Dummy column_________________________._________________ 38

Discussion of centrifuge data____----__----------_--_------------ 40

Comparison of crucible and box methods_____________________ 40

Effect of temperature in the controlled-temperature centrifuge. _ 40 

Comparison of controlled- and uncontrolled-temperature centrifuges_ _---_-______________________-____-__--_-_-_----- 43

Effect of length of period of centrifuging____________________ 47

in
IV CONTENTS

Investigation of centrifuge moisture content Continued

Discussion of centrifuge data Continued Page

Effect of applied tension__________________________________ A47

Force times gravity__--___----_--__--____-__--___-_____ 49

Sample thickness______________________________________ 51

Dummy column,______________________________________ 54

Comparison of disturbed and undisturbed samples.____________ 55

Summary and conclusions __________________________________________ 57

Investigation of column drainage________________________________ 57

Investigation of centrifuge moisture content ______________________ 58

Selected references________________________________________________ 59

ILLUSTRATIONS

Page 

FIGURE 1. Assembly for segmented column___________________________ A7

2. Large cylinder sample of an alluvial sand___________________ 8

3. Methods of drainage..___________________________________ 11

4. Effect of cleaning 0.47-mm glass beads_____________________ 13

5. Moisture retained in 0.120-mm glass beads after draining by

several methods.______________________________________ 14

6. Moisture retained in alluvial sand after 2 weeks of draining by

simple free-drainage method.___________________________ 16

7. Quantity of water drained from 0.120-mm glass beads 1 y two

methods_ _ ___-_-______---___-___-____--_---___--__-- 17

8. Quantity of water drained from an alluvial sand_____________ 17

9. Moisture retained in glass beads after drainage.-____________ 18

10. Effect of column diameter on drainage of 0.120-mm glass beads. 19

11. Moisture distribution in an 8-inch-diameter column________ 20

12. Quantity of water drained from 0.120-mm glass beads after

wetting by several methods.-___________________________ 21

13. Moisture retained in 0.120-mm glass beads after wetting by

several methods.______________________________________ 22

14. Effect of load on amplitude of packer-.-----.-------------- 24

15. Effect of surcharge packing on porosity.-___-_-_-____--__-- 25

16. Effect of amplitude on porosity__ _________________________ 26

17. Effect of vibration on porosity.--_---_---__------_-_------ 27

18. Distribution of porosity in a long column of 0.120-mir glass

beads-.-_____._-._______-____-_________--_-_--_---.-- 29

19. Distribution of porosity in long columns of 20-mesh Del Monte

sand. ________________________________________________ 30

20. Settling throughout a long column of glass beads.----------- 31

21. Effect of fluorescein dye on quantity of water drained______ 33

22. Effect of fluorescein dye on moisture retained after drainage-- 34

23. Effect of time on drainage from an alluvial sand_____________ 35

24. Centrifuge equipment for crucible and box methods....______ 37

25. Large-size dummy column and accessory centrifuge equipment. 39

26. Effect of temperature in controlled-temperature centrifuge on

the centrifuge moisture content of coarse-textured materials. 41

27. Effect of temperature in the controlled-temperature centrifuge

on the centrifuge moisture content of fine-textured materials. 42
CONTENTS V

Page

FIGURE 28. Effect of length of period of centrifuge operation on the centrifuge moisture content._________________________________ A43

29. Effect of temperature in the uncontrolled-temperature centrifuge on the centrifuge moisture content __________________ 45

30. Effect of length of period of centrifuging in the controlledtemperature centrifuge on centrifuge moisture content- _ _ __ 48

31. Effect of force times gravity on centrifuge moisture content for

coarse-and medium-textured materials___________________ 50

32. Effect of force times gravity on centrifuge moisture content for

medium- and fine-textured materials.____________________ 50

33. Moisture content at different heights within sample after centrifuging. _______________________________________________ 52

34. Effect of sample thickness on centrifuge moisture content_____ 53

35. Centrifuge moisture equivalent compared with centrifuge moisture content obtained with porvic dummy columns. _______ 55

36. Effect of length of time of centrifuging on the centrifuge moisture content of samples placed on a 2-centimeter porv'c 

dummy column_______________________________________ 56

TABLES

Page 

TABLE 1. Particle-size distribution of materials _______________________ A5

2. Chemical analysis of water from Denver, Colo_______________ 9

3. Amplitude of vibration for unloaded Syntron packer_---_____- 23

4. Comparison of settling with vibration_______________________ 23

5. Centrifuge moisture equivalents of selected materials. ________ 36

6. Moisture equivalents obtained by crucible and box methods ___ 40

7. Centrifuge moisture content obtained from the controlled- ard

uncontrolled-temperature centrifuges. ____________________ 46

8. Moisture content after centrifuging samples of fine-text ured

materials, 3 centimeters thick_______--------___--_----_-_ 52

9. Comparison of centrifuge moisture values at % atmosphere

tension for disturbed and undisturbed samples.____________ 56
HYDROLOGIC PROPERTIES OF EARTH MATERIALS

SPECIFIC YIELD COLUMN DRAINAGE AND 

CENTRIFUGE MOISTURE CONTENT

By A. I. JOHNSON, R. C. PRILL, and D. A. MORRIS

ABSTRACT

The specific yield of a rock or soil, with respect to water, is the ratio of 

(1) the volume of water which, after being saturated, it will yield by gravity 

to (2) its own volume. Specific retention represents the water retained against 

gravity drainage. The specific yield and retention when added together are 

equal to the total interconnected porosity of the rock or soil. Because specific 

retention is more easily determined than specific yield, most methods for 

obtaining yield first require the determination of specific retention.

Recognizing the great need for developing improved methods of determining 

the specific yield of water-bearing materials, the U.S. Geological Survey and 

the California Department of Water Resources initiated a cooperative investigation of this subject. The major objectives of this research are (1) to 

review pertinent literature on specific yield and related subjects, (2) to increase 

basic knowledge of specific yield and rate of drainage and to determine the 

most practical methods of obtaining them, (3) to compare and to attempt to correlate the principal laboratory and field methods now commonly used to obtain specific yield, and (4) to obtain improved estimates of specific yield of water-bearing 

deposits in California. An open-file report, "Specific yield of porous media, 

an annotated bibliography," by A. I. Johnson, D. A. Morris, and R. C. Prill, 

was released in 1960 in partial fulfillment of the first objective.

This report describes the second phase of the specific-yield study by the 

U.S. Geoligical Survey Hydrologic Laboratory at Denver, Colo. Laboratory 

research on column drainage and centrifuge moisture equivalent, two methods 

for estimating specific retention of porous media, is summarized.

In the column-drainage study, a wide variety of materials was packed into 

plastic columns of 1- to 8-inch diameter, wetted with Denver tap water, and 

drained under controlled conditions of temperature and humidity. The effects 

of cleaning the porous media; of different column diameters; of dye and time 

on drainage; and of different methods of drainage, wetting, and packir? were 

all determined. To insure repeatability of porosity in dupliacte columns, a 

mechanical technique of packing was developed.

In the centrifuge moisture-content study, the centrifuge moisture-equivalent 

(the moisture content retained by a soil that has been first saturated and then 

subjected to a force equal to 1,000 times the force of gravity for 1 hour) test 

was first reviewed and evaluated. It was determined that for reproducible 

moisture-retention results the temperature and humidity should be controlled 

by use of a controlled-temperature centrifuge. In addition to refining this

Al
A2 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

standard test, the study determined the effect of length of period of centrifuging and of applied tension on the drainage results.

The plans for future work require the continuation of the laboratory standardization study with emphasis on investigation of soil-moisture tension and 

unsaturated-permeability techniques. A detailed study in the field then will be 

followed by correlation and evaluation of laboratory and field methods.

INTRODUCTION

The specific yield of a rock, or soil, with respect to water, is the 

ratio of (1) the volume of water which, after being saturated, it 

will yield by gravity to (2) its own volume (Meinzer, 1923, p. 28). 

Specific retention represents the water retained against gravity drainage. The specific yield and retention when added together are equal to 

the total interconnected porosity of a rock or soil. That is, any 

isolated openings that do not take part in the draining and refilling 

of a body of rock or soil are not counted as a part of the total porosity 

as used here.

Gravity ground water is available free water, or the water that 

will be. withdrawn from a given body of rock or soil in the zone of 

saturation by the direct action of gravity if the water table and capillary fringe move downward to a new position that is below the top 

of the given body. The distinction between gravity water and retained water is not entirely definite because the amount of water that 

will drain out depends on the length of time it is allowed to drain, on 

the temperature and mineral composition of the water (which affect its 

surface tension, viscosity, and density), and on various physical relations of the body of rock or soil.

Because specific retention is more easily determined than is specific 

yield, most methods for obtaining specific yield first require the determination of specific retention. As indicated above, specific yield may 

then be found by subtracting the specific retention from the total 

porosity.

OBJECTIVES AND PROPOSED SCOPE OF BESEABCH PBOGEAM

Recognizing the great need for developing improved methods of 

determining or estimating specific yield of water-bearing materials, 

the U.S. Geological Survey and the California Department of Water 

Resources began a cooperative investigation of this subject in July 

1957.

The major objectives of this research program are as follows:

1. To review pertinent literature and to prepare an annotated bibliography on specific yield and related subjects. (See Johnson and 

others, 1960.)

'2. To increase basic knowledge of specific yield and rate of drainage 

and to determine the most practical methods of obtaining them for 

general application.
SPECIFIC YIELD A3

3. To compare and attempt to correlate the principal laboratory and 

field methods now commonly used for estimating specific yield and 

to investigate or develop additional methods as advisable.

4. To obtain improved estimates of the specific yield of water-bearing 

deposits in California.

As a first step toward accomplishing the last three objectives, a 

preliminary study was made of the drainage and centrifuge moisture 

equivalent of porous media, so that these procedures and techniques 

could be evaluated and standardized.

REVIEW OF PREVIOUS WORK

Israelson (1918) made a series of field tests of water-retaining 

capacities of different soil types in the Sacramento Valley, Calif. His 

method was to determine the porosity of the different soils and their 

water content at successive depths, immediately before irrigation and 

again about 4 days after irrigation. This second determination gave 

approximately the specific retention after a short drainage time.

Ellis and Lee (1919) made experiments on valley fill along the 

major stream valleys of San Diego County, Calif. Their method 

involved the collection of samples immediately above the capillary 

fringe after a decline of the water table.

Clark (1916) in his studies of the Morgan Hill area, California, 

observed the lowering of the water table, and hence the volume of 

sediments drained by pumping a measured volume of water. The 

specific yield was then obtained using the ratio of the volume of 

water pumped to the volume of sediments drained.

The recharge method (Meinzer, 1923) also has been used to determine specific yield by observing the amount of water that percolates 

from streams or canals into an aquifer and the resulting rise of the 

water table. From the volume of sediments saturated by the measured 

recharge, specific yield may be computed.

In addition to the above field approaches to specific yield, several 

laboratory tests have been used to determine specific retention.

Hazen (1891) presented the results of tests of the water-retaining 

and water-yielding capacities of filter sands. These tests related 

specific yield and specific retention to the effective size of grain as 

obtained from mechanical (particle-size) analyses. King (1898) 

presented the results of tests of the water-yielding and water-retaining capacities of five sorted sands of different grain size; these sands 

were saturated and then allowed to drain over a long period of time. 

The results of King's tests showed some discrepancy between the 

porosity and total water and seemed to give lower values for specific 

retention than Hazen's tests, especially for the coarser samples. Eckis 

and Gross (1934) related particle-size analysis and porosity to specific

690-146 O 63 2
A4 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

retention in their storage-capacity studies of the South Coastal basin, 

California.

The centrifuge-moisture-equivalent method for testing moistureretention capacity of a soil was introduced by Briggs and McLane 

(1907) by determinations on more than 100 soils. Although their 

original work was done under a centrifugal force of 3,000 times 

gravity, they suggested in a later publication (1910) that a force 

of 1,000 times gravity could be used. In 1912, Briggs and Shantz 

made moisture-equivalent tests using 1,000 times gravity; since 

that time this procedure has been accepted as standard by most investigators. However, even though this has been the standard, many 

separate investigations have been made since 1912 concerning the 

relation of the moisture equivalent obtained to factors such as, effect 

of prestorage methods, preliminary sample preparation, temperature 

during saturation and centrifuging, depth of sample, sealing of top 

of sample cups, force times gravity, length of time of centrifuging, 

and method of drying centrif uged samples.

The centrifuge moisture equivalent may be adjusted by a correction 

factor proposed, by Piper (1933), based on data obtained by drainage 

of columns of natural materials under field conditions. Tl is adjusted 

value, considered to be specific retention, is then subtracted from the 

porosity to obtain specific yield.

This summary of past work will serve to place the current study 

in perspective and account for the direction that the work has taken.

OBGANIZATION OF INVESTIGATION

The report was prepared under the general supervision of J. F. 

Poland, research geologist, G. F. Worts, Jr., formerly district geologist, and H. D. Wilson, district engineer for California, Ground 

Water Branch of the Geological Survey, and under the direct supervision of the senior author, who is chief of the Hydrologic Laboratory, 

Denver, Colo.

ACKNOWLEDGMENTS

Many individuals contributed to this report by giving advice and 

furnishing information relative to the problem. Valuable assistance was provided by Mr. L. B. James, chief geologist, and Mr. R. T. 

Bean, supervising engineering geologist, both of the California 

Department of Water Resources.

INVESTIGATION OF COLUMN DRAINAGE

TECHNIQUE 

MATERIALS

Homogeneous materials were used in the investigation < ' of column

drainage. Glass beads (3M "Superbrite," Minnesota Mining and
SPECIFIC YIELD A5

Manufacturing Co.) and sand (DM-20-Del Monte Properties Co.) 

were selected as the principal testing materials because they are available in a large range of sizes and because their physical properties 

are controlled, within narrow limits. Glass beads are nearly spherical 

and are manufactured in a range of sizes from 0.028 to 0.59 mm. 

In this study, code Nos. 107 (0.470 mm medium-sand size), 112 

(0.120 mm very fine sand size), and 118 (0.036 mm upper silt size) 

glass beads were used. Del Monte sand, a beach or dune sand from 

California and Idaho, is available in several mesh sizes: 16, 20, 30, 

or 60 mesh. The 20-mesh size, which is classified as a coarse sand, 

was used in this study. In addition, carefully selected fine sands 

from field sites near Fresno, Calif., and Ilolbrook, Ariz., were used. 

(See table 1 for particle-size distribution of materials used.)

TABLE 1. Particle-size distribution of materials 

[Results in millimeters]

Sample

Glass beads: 

0.036 mm _____ ..

0.120mm.. _ ......

0.470 mm. _ . _ ..

Del Monte sand: 

20 mesh_... __ . ... 

30 mesh.... _ . 

60 mesh-... _ ...--

Alluvial sand (Hoibrook, Ariz.)- 

58ARK146 .--- _ ...

57CAL2.. ..... .........

14 

66.- 

72. 

57CAL106. -----

110.. .

112...... ....

118 

122.. 

123.. 

139 

152.. .... -------

155 

162.,- ___ ......

173.. 

205.. .

59CAL130-131 .. ___ -

137-138..... .

59CAL191-244 . .

191-248-. .

251-252.. .

253-254.. ---.-.-

258-261-. .

580KL15 .-..-- ...

42 .

Fuller's earth.... _ . ...

Kaolin (EPK) .

Kaolin (N.F.)

Loess:

Clay 

«0.004)

3.4

 -- -

2.

2.

71.6

52.0

71.5

7.2

9.8

17.0

7.2

57.0

6.5

7.0

26.8

9.0

22.2

16.2

26.0

26.2

21.4

4.

20.2

10.5

16.7

7.7

24.8

30.0

54.0

no fl

16.6

Silt 

(0.004- 

0.0625)

96.2

9

0

27.8

37.3

19.7

1.6

9 7

41.2

8.0

42.0

7.3

2.6

61.2

43.6

37.8

37.6

58.8

oc e

37.6

3

41.3

38.5

28.5

26.5

48.2

45.6

7.0

79 8

Very 

fine 

(0.0625- 

0.125)

0.4

1.6

.1 

.1

20.1

11.0

.6

5.5

4.0

6.0

7 ft

90 9

6.6

.2

17 S

2.4

7.0

32.8

30.0

H o

9 6

4.6

6.8

16.6

91 A.

20.2

on Q

17.0

16.0

11.6

4.6

3.4

J

Fine 

(0.125- 

0.25)

47.8

.5 

10.5

45.1

56.0

2

0

2.8

49.2

31.6

.2

15.6

3.6

13.4

15.2

4.0

5.0

11.5

17.3

16.0

91 S

9 8

4

0

0 2

3and

Medium 

(0.25- 

0.5)

9.6 

86.1

31.9

30.0

1.6

2.0

36.0

36.3

4

0

.4

5.4

1.0

11.4

6.2

1 9

2.4

49 3

8 9

n

o

.2

.2

.6

3.6

Coarse 

(0.5-1)

18.0

85.0 

3.3

1.0

.7

.1

.2

14.2

.2

.1

.2

22.4

0.8

1.6

2.4

4.8

1.4

Very 

coarse 

(1-2)

4.8

.1

.7

1.2

.2

.2

Very 

fine

(2-4)

-----

1.9

.2

3ravel

Fine

(4-8)

1.9

Med'urn 

(8-16)

0.6

Sort- ing i 

coefficient

So

1.2

1.1

1.0

1.1 

1.2

1.4

1.4

.4

1.8

3.0

1.4

2.6

1.3

1.4

3.2

2.2

5.1

2.7

5.6

3.4

3.6

4.9

1.4

4.3

2.4

2.3

3.7

3.9

3.4

1.7

1 Sorting coefficie 

where

Z>7,>=particle diameter for which 75 percent are smaller. 

Z>25=particle diameter for which 25 percent are smaller.
A6 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

COL.TIMNS

The drainage columns were made by filling transparent plastic tubing, having an inside diameter of % to 8 inches (and a wall thickness 

of %6 to % in.) with media. The plastic tubing was used either as 

manufactured or subdivided into 1- to 2-inch-long segments which 

were placed end to end and built into leak-proof columns by use of 

a filament pressure-sensitive tape (Tuck Tape type I) and hose clamps, 

or by a pressure brace. (See fig. 1.) The lower end of erch column 

was fitted with a 115-mesh copper screen or bronze filter disk laid 

across a singly perforated rubber stopper, sealed, and held in place 

by use of adhesive tape.

The undisturbed alluvial sand sample from the flood plain of the 

Little Colorado River near Holbrook, Ariz., was taken in a 5-inch 

plastic cylinder, about 5 feet long, by the method of advance trimming. By this method the sampling cylinder was advanced carefully 

downward into a short column of material; and as the cylinder's 

cutting edge advanced, the material was trimmed roughly to about ^ 

to 1 inch ahead of the cutting edge. This process continued, an excavation being dug as the sampling cylinder advanced. When the 

sample protruded above the top of the cylinder, the excess sample was 

trimmed away and steel plate was placed on top of the cylinder. The 

sample cylinder with the retained sample was removed carefully from 

the excavation, and the sample was trimmed flush with the lower end 

of the cylinder. A steel base plate was then placed on the lower end 

of the cylinder. The sample was confined in the sampling cylinder 

by the use of long threaded rods tightened between the upper and 

lower plates of the sampling cylinder. ('See fig. 2.) In the laboratory, the steel base plate was replaced by a plastic base plate containing a fritted-bronze filter disk.

PACKING

The manual method of packing was used for the initial drainage 

work. This method involved gently tapping the side of the column 

with a rubber mallet as the material was added in small increments. 

Vertical columns of material 6 inches in height were added successively and tapped until no change in volume occurred. This process 

was continued until the columns were filled. Packing techniques employing this manual method of vibration were especially difficult to 

control, and the porosity of glassbead media throughout segmented 

columns ranged from about 34 to 40 percent (porosity was used as 

an index of the packing effects). This range of porosity using glassbead media was considered to be too wide for research; and considering that the range would be even greater for more natural materials, 

a more efficient method of packing was sought. The literature was 

reviewed for a solution to the problem, but very little dr.ta on me-
SPECIFIC YIELD A7

Pressure plate

SCALE 

lcm=4crr

FIGURE 1. Assembly for segmented column.

chanical packing pertaining to this application were discovered. It 

was apparent that additional laboratory study was needed to' evaluate 

this problem and to develop a better packing technique. After a cur-
A8 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

FIGURE 2. Large cylinder sample of an alluvial sand.

sory study of several commercial packers, including jolting as well 

as oscillatory equipment, the Syntron VP-60 packer was chosen as 

the most suitable for the evaluation.

WETTING FLUID

De-aired Denver tap water was used as the wetting fluid. The air 

was removed by means of a vacuum apparatus especially designed in 

the laboratory. The chemical analysis of the water is shown in 

table 2.

OBSERVATION OF WATER

De- aired water and de-aired water containing green dye (0.307 gram 

fluorescein dye per liter) were used as the saturation fluids. Observation under white light and under ultraviolet light indicated that the
SPECIFIC YIELD A9

TABLE 2. Chemical analysis of water from Denver, Colo.

Concen- Concentration tration 

Chemical constituent l (ppm) Chemical constituent l (ppm)

Calcium (Ca)_______________ 20 Nitrate (NO3) -------------- .6

Magnesium (Mg)______________ 4 Dissolved solids___--___---_-__ 99

Sodium (Na) and potassium (K)_ 3. 4 Hardness (as CaCOs)__________ 66 Bicarbonate (HCO3 )-__-,_______ 47 

Sulfate (SOO_________________ 31 Specific conductance

Chloride (Cl)____________. 1.5 (micromhos at 25° C)__ 161

Fluoride (F)______________ .2 pH________________________ 7.3

1 Analysis by Quality of Water Laboratory, U.S. Qeol. Survey, Denver, Colo.

visual line of saturation was as easily discernible when usirg plain 

de-aired water as when using de-aired water containing the fluorescein 

dye. Under ultraviolet light, the intensity of fluorescein changed near 

the wetting or drying front, but the change was so gradual that the 

eye could barely detect it.

CLEANING OF POROUS MEDIA

An attempt was made to determine whether acid cleaning would 

affect the wetting characteristics of glass beads. Using a solution of 

dichromate cleaning reagent (35 ml saturated potassium dichromate 

solution added to 965 ml of concentrated sulfuric acid), 0.47-mm glass 

beads were thoroughly acid washed and drained. After thorough 

flushing with de-aired water, the beads were subjected to tl ?, usual 

wetting and draining treatment given to unwashed beads.

METHODS OF WETTING

Four methods were used to evaluate the effect of wetting on the 

pattern of moisture distribution after drainage. In the first 3 methods 

segmented columns, iy2 inches in diameter and 50 inches in length, 

were used; in method 4, a segmented column, l 1/^ inches in diameter 

and 70 inches in length was used. The 4 columns were filled with 

0.120-mm glass beads and wetted from below.

In the first 3 methods of wetting, a head of water was maintained 

at a level of 48 inches above the bottom of the columns. In method 1, 

a wetting period of 76 hours was used. In method 2, a wetting period 

of about 120 hours was used; during the last 19 hours de-aired water 

was allowed to flow through the column. In method 3, an initial wetting period of about 77 hours, a drainage period of about 19 hours, 

and a rewetting period of about 25 hours were used. In method 4, 

the water was maintained at a level of 50 inches above the bottom of 

the column, and the column was wetted for a period of about 73 hours, 

allowing the capillary fringe to develop above the water tabK

In wetting the larger diameter columns of glass beads, wettingmethod 1 was used. This technique was also used for the Holbrook 

alluvial sand sample, except that the column was wetted slowly for 

about a year before drainage.
A10 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

An attempt was also made to use the vacuum technique in wetting 

small-diameter segmented columns of glass beads. In this method, 

vacuum was applied as the segmented columns (segments 1 ^ld together 

in a pressure brace) were submerged in water in an air-tight chamber. 

The vacuum was ineffective in the removal of air at the contact between segments. This was caused by the very close tolerances between 

adjacent milled segments as held together under pressure.

METHODS OF DRAINAGE

Two, basic methods of drainage were employed to determine the 

effect of the method of drainage on the amount and rate of drainage 

and the moisture distribution after drainage. These were designated 

"free-drainage" and "hanging-water-column" methods. Two methods 

of free drainage, the simple and extended-base, and two methods 

of hanging-water-column drainage, the nonmembrane and membrane, 

were used. In all tests the columns were packed with 0.120-mm glass 

beads.

All columns were allowed to drain until discharge had virtually 

ceased, and the rate was recorded.

In the simple free-drainage method, columns from % to 8 inches 

in diameter and measuring as much as 70 inches in length were used. 

The drained water was discharged from a short length of glass tubing 

fitted in a rubber stopper at the lower end of the drairage column. 

(See fig. 3)

In the extended-base method, a column iy2 inches in diameter and 

53 inches in length was placed with the bottom end in contact with a 

bed of 0.120-mm glass beads contained in a column that was 4 inches 

in diameter and 17 inches in length. Drained water was discharged 

from the bed of glass beads through a short length of glass tubing 

fitted in a rubber stopper at the lower end of the bed. (£?,e fig. 3.)

In the nonmembrane hanging-water-column method, a column l1/^ 

inches in diameter and 53 inches in length was used. A 17-inch water 

column consisting of a flexible plastic tubing and lower wr.ter chamber 

completely filled with water was attached to the lower end of the 

column. The drained water was discharged through a glass tubing 

fitted to the upper end of the water chamber. (See fig. 3.)

In the membrane method a column iy2 inches in diameter and 16 

inches in length was used. A semipermeable plastic membrane (Porvic 

Filter Sheet, Grade "M," Pritchett & Gold, London) was placed 

in contact with the 0.120-mm glass beads at the lower end of the 

column, and a 104-inch water column was extended from the porvic 

in a manner similar to that used in the nonmembrane method. (See 

fig. 3.) The advantage of the membrane over the nonmembrane 

method is that a longer water column can be used, thus reducing the 

length of sample column required for free drainage. Any water
SPECIFIC YIELD All

Screen x

SIMPLE EXTENDED-BASE 

FREE-DRAINAGE METHODS

NONMEMBRANE MEMBRANE

HANGING-WATER-COLUMN METHODS 

FIGURE 3. Methods of drainage.

column less than 18 feet long can be used with the porvic membrane, 

whereas, with the nonmembrane method, the length of the water 

column to be effective cannot exceed the height of the zone of capillary 

saturation of the sample.

690-14S O 63-
A12 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

In the drainage of the larger diameter columns, the water table 

was maintained at the bottom of the column. This was done by positioning the discharge tube of the outflow bottle at the bottom of 

the column. The Holbrook sample was drained by two methods the 

simple free-drainage method and the nonmembrane hanging-watercolumn method. In the latter method a 48-inch hanging-water column 

was applied.

METHODS OF SAMPLING MOISTURE DISTRIBUTION

The pattern of moisture distribution after drainage was obtained 

by sampling the drainage column in 1- or 2-inch increments after 

discharge had virtually ceased and by determining the moisture content for each increment. The sample was taken by rn^ng a long 

spoonlike rod in the small-diameter continuous columns, by using a 

soil-sampling tube or by sliding the column away from the media 

in the large-diameter continuous columns, and by separating the 

sections of the small-diameter segmented columns.

CONTROLS EMPLOYED

The drainage work was done in a room where the humidity was controlled at 40 to 45 percent and the temperature maintained at 20°C. 

Evaporation from taped segmented columns was reducec1 to a minimum by sealing the top of each column with cellophane tppe through 

which a single 1-mm perforation was made. Evaporation from 

pressure-held segmented columns was reduced by the use of a flexible polyethylene jacket, which was wrapped around the column and 

held together by use of a "Velcro" nylon tape fastener. TYa, humidity 

within the jacket was thereby kept higher than the normal room 

humidity (40 percent).

DISCUSSION OF DRAINAGE DATA 

EFFECT OF CLEANING POROUS MEDIA

To determine the effect of acid cleaning on glass-bead media, the 

pattern of moisture distribution after drainage for washed and unwashed 0.47-mm beads was compared. (See fig. 4.) There data suggest that washing with the dichromate solution has little or no effect 

on the moisture-retention characteristics of the glass beads and is 

therefore unnecessary.

COMPARISON OF DRAINAGE METHODS

The data in figure 5 indicate the pattern of moisture distribution, 

after drainage at different heights above the water table in 0.120-mm 

glass beads by the 4 different methods of drainage (simple, extendedbase, nonmembrane, and membrane; fig. 3). The moisture data were 

obtained gravimetrically by sampling after the column had drained. 

In the first 3 methods the glass beads were wetted once from below
SPECIFIC YIELD A13

24

22

20

18

16

14

O 12

EXPLANATION

Unwashed beads

o 

Acid-washed beads

0 48 12 16 20 24 28

MOISTURE CONTENT, IN PERCENT BY WEIGHT 

FIGURE 4. Effect of cleaning 0.47-mm glass beads.

for about 90 hours. Beads in the membrane column were wetted 

from below through the membrane for about 1 week. Except at the 

higher moisture contents, the percentages of retained wT ater for the 

first 3 methods compare closely throughout the total moisture range.
A14 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

120

110

100

4 8 12 16 20 2A 

MOISTURE CONTENT, IN PERCENT BY WEIGHT

28

FIGURE 5. Moisture retained in 0.120-mm glass beads after draining by several

methods.

In the membrane method moisture content was obtained for heights 

of 104 to 120 inches above the Avater table. The values of retained 

moisture were similar to those obtained by the other 3 methods at
SPECIFIC YIELD A15

52 to 68 inches above the water table; thus, the moisture retention 

in the 0.120-mm glass beads was approximately 1.7 percent at any' 

height above 52 inches.

The pattern of moisture distribution after simple drainage of the 

Holbrook alluvial sand is shown in figure 6. The pattern of moisture 

distribution is not so uniform as that obtained from drainage of glass 

beads,'but the nonuniformity is undoubtedly due to slight differences 

in texture existing in this undisturbed column of natural sediments.

A comparison of the volume of water drained in relation to time 

for the simple free-drainage method and the nonmembrane hangingwater-column method is shown in figure 7. In the simple freedrainage method the drainage column was 70 inches long; in the 

nonmembrane hanging-water-column method the drainage column was

53 inches long, and the hanging-water column was 17 inches long. 

The distance from the top of the drainage column to the bottom of the 

hanging-water column was thus the same length as the drainage 

column used in the simple free-drainage method. The columns were 

wetted once from below and drained until moisture equilibrium was 

approached. Although the total volumes of water discharged from 

the 2 columns differed by only 10 cc, the initial rate of discharge was 

higher for the hanging-water-column method. This is the expected 

relationship, even though there was no difference in applied tension 

between the two columns, because a hanging-water column would 

facilitate the discharge of water initially, owing to a higher permeability at the outlet.

For the Holbrook alluvial sand the rate of drainage using the 48- 

inch hanging-water column was much higher, and the total quantity 

discharged was about 20 percent higher than the amount obtained by 

simple free drainage. (See fig. 8.) This relationship seems reasonable, because tension was applied by the hanging-water column and 

the effect of the capillary fringe was eliminated. To get conparable 

results in total-discharge data, equal tension must be applied to the 

drainage columns either by using longer columns, hanging-water 

columns, or vacuum.

The pattern of retained moisture for simple free drainage of 3 

materials, 0.470-mm glass beads (medium-sand size), 0.120-mm glass 

beads (very fine sand size), and 0.036-mm glass beads (coarse silt size), 

is shown in figure 9. These drainage values were determined after the 

materials had been wetted only once and then allowed to drain for 23 

to 72 hours without applied tension.

EFFECT OF COLUMN DIAMETER

It was important to evaluate by a single method of drainage the 

efl'ect of column diameter on the moisture distribution after drainage. 

Figure 10 shows the moisture distribution after drainage of mechan-
A16 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

50

46

42

38

30

22

18

14

10

r

4 8 12 16 20 24 

MOISTURE CONTENT, IM PERCENT BY WEIGHT

28

FIGURE 6. Moisture retained in alluvial sand after 2 weeks of draining by 

simple free-drainage method.

ically packed 1-, 4-, and 8-inch-diameter columns of 0.120-mm glass 

beads. The diameter of the column of drainage materials makes 

little difference in the general pattern of the moisture distribution
SPECIFIC YIELD A17

Hanging-water column (nonmembrane) 

Free drainage (simple)

12 16 20 24 28 32 36 40 44 48 

ELAPSED TIME. IN HOURS

FiGtTKE 7. Quantity of water drained from 0.120-mm glass beads by two methods.

3800

EXPLANATION

Hanging-water column 

Free drainage

0 6 12 18 24 30 36 42 48 54 60 66 72

ELAPSED TIME, IN HOURS 

FIGCKE 8. Quantity of water drained from an alluvial sand.

after drainage. In large columns it makes little difference whether 

the samples are taken at the side of the column or in the middle. 

Figure 11 shows the moisture distribution at both sides and in the 

middle of the 8-inch-diameter column.

EFFECT OF METHOD OF WETTING

The quantity of water drained after wetting by three methods is 

shown in figure 12. The data indicate fairly close agreement between 

the first two methods and the first drainage of the third method (2
HYDROLOGIC PROPERTIES OF EARTH MATERIALS

I I 

EXPLANATION

0.470- millimeter glass beads

B 0.120- millimeter glas? beads

o 

C 0.036- millimeter glas~ beads

0.036-millimeter glass beads

Wifn 48-inch membrane hanging wote

column

4 8 12 16 20 

MOISTURE CONTENT, IN PERCENT BY WEIGHT

FIGURE 9. Moisture retained in glass beads after drainage.

wettings 2 drainages) OB the quantity of water drained. The data 

for the second drainage of method 3 show that drainage is considerably less, which may be explained by greater air entrapment on rewetting the moist sample.
SPECIFIC YIELD A19

/u

60

50

CO

LLJ

I 

O

z 

z

COLUMN

-t

O

CO

S? 30 CO

UJ

>

O

CO

<

1-

LJJ 

X 20

10

0

I

I

1

1

9)

XQ

Q

«

3

 o

X

$ 3

EXPLANATION

1-inch column

O 

4-inch column

X

8-inch column

<*

 i

>

c

1

1<*

G»

0*

C

IP

0 5 10 15 20 25 30 

MOISTURE CONTENT, IN PERCENT BY WEIGHT

FIGURE 10. Effect of column diameter on drainage of 0.120-mm glass beads.

The distribution of retained moisture after drainage of the columns 

wetted by the four methods is shown in figure 13. Although the 

capillary-rise method was not comparable in technique to the other 

methods, the data indicate fairly close agreement between all methods. 

The one-wetting method therefore seems adequate for most purposes.

690-146 O 63 4
A20 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

70

60

50

</)

CO

LLJ 30

O

03

20

EXPLANATION

Location A: side

Location B: middle

O

Location C: side

10

-o

0 5 10 15 20 25 30 

MOISTURE CONTENT, IN PERCENT BY WEIGHT

FIGURE 11. Moisture distribution in an 8-inch-diameter column. 

EFFECT OF PACKING METHOD

As mentioned earlier, the Syntron VP-60 vibratory packer was 

chosen as the most appropriate commercial packer for rtudy. The 

following discussion describes the development of a laboratory technique of packing that uses this equipment. Unless noted otherwise, 

0.120-mm glass beads were used for all packing experiments.
180

10 12 

ELAPSED TIME. IN HOU

FIGURE 12. Quantity "f wat^r drained from 0.120-mm glass h«»ads 
A22 HTDROLOGIC PROPERTIES OF EARTH MATERIALS

70

60

50

40

30

20

10

EXPLANATION 

One wetting

Flow wetting

O 

Two wettings

X 

Capillary-rise wetting

5 10 15 20 25 

MOISTURE CONTENT, IN PERCENT BY WEIGHT

30

FIGURE 13. Moisture retained in 0.120-mm glass beads after wetting by several methods. 

CHARACTERISTICS OF PACKER

The Syntron VP-60 packer is virtually a noiseless vibratory packer 

built for loads as much as about 300 pounds. It has a rheostat control 

for amplitude adjustment and a fixed frequency of 60 vibrations per 

second (or line frequency). The operational characteristics of the 

packer were obtained by determining the peak-to-peak amplitude of 

the vibratory platform at five mechanical settings of tl -^ rheostat. 

Table 3 shows the small variations in amplitude that were measured 

by a General Electric vibrometer.

The change in amplitude at an arbitrarily chosen rheostat reading 

(B) with change of weight on the vibrator platform was tr<m studied.
SPECIFIC YIELD A23 

TABLE 3. Amplitude of vibration, in centimeters, for unloaded Syntron packer

Rheostat setting

Minimum __ _ ___ A_____. _______ _______:_.____ _____ __

B-_-___________ _._.___..___. _____ _.

c___. .______._______..___.____..__.__

D_. ___________________ ___

i

0 04

07

no

13

IS

R

2

0 04

07

09

13

18

on

3

0.04

.06

.09

. 12

. 19

4

0 04

06

09

12

18

This was done throughout the capacity range of the packer 17 adding 

glass beads by 10-pound increments to a large cylindrical tube that 

was rigidly attached to the packing platform. Figure 14 shows the 

variation in amplitude with load a decrease of 0.055 cm in amplitude occurring as the load increased from 13.5 to 300.0 pounds. 

Seventy-five percent of the change in amplitude took place in the 

first 80 pounds of loading. Only 15 percent additional change took 

place over the 80- to 100-pound interval, and the remaining 10 percent change took place beyond 180 pounds.

EFFECT OF VIBRATION ON SETTLING

A study was made of the effect of vibration on the amount of settling 

in a 4-foot column of glass beads. Table 4 shows the total amount 

of settling for vibration from 1 to 300 seconds.

TABLE 4. Comparison of settling with vibration

Total time

of vibration

(seconds)

1 _______

2 _______

3 _______

4 _______

Total amount

of settling 

(centimeters)

_____ 2.2 

_____ 2. 8 

_____ 3. 3 

_____ 3. 7

Total time

of vibration

(seconds)

5 ______

10 ______

300 ______

Total amount

of settling 

(centimeters)

._______ 4. 0

_____ 4. 3 

.____ 6. 0

About 66 percent of the settling took place over the first 10 seconds 

of vibration; about 33 percent took place during the first second of 

vibration.

DEVELOPMENT OF PACKING TECHNIQUE

After operational characteristics of the packer became known, the 

most convenient method of adding media was arbitrarily selected 

to fill the column completely with media by a tremie techrique and 

then apply vibration. The effects of surcharge and amplitude were 

determined by employing this method on a 294-cubic cm cylinder 

(filled with 0.120-mm glass beads) 5 cm in diameter and 14.5 cm 

long. Porosity was used as an index of these effects on packing.

EFFECT OF SURCHARGE

The effect of surcharge was determined by obtaining porosities 

with and without the use of a 200-gram weight placed on the glass
A24 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

0.060

0.055

0.050

0.045

0.040

0.035

0.030

0.025

0.020

0.015

0.010

0.005

I I i T

40 80 120 160 200 

LOAD, IN POUNDS

240 280 310

FIGURE 14. Effect of load on amplitude of packer.

beads during vibration. Figure 15 shows this effect at. a rheostat 

setting of B (0.09-cm amplitude) for total vibration of 25 to 200 

seconds. The effect of the use of surcharge on porosity wa?1 negligible 

over the period of vibration. The porosity, as determined by the
SPECIFIC YIELD A25

280

275

250 

225

Q

0 20° 

CJ 

UJ

z" 175

O

1 

1 150

u_ 

O

uj 125

(=

j5 100

0

75

50

25

0

n

> /

~

;

-

-

-

-

-

y.

0 

0 <

 0

0 

i

EXPLANATION

Without surcharge ~"

O

With 200-gram surcharge

>

_

" 

-

-

^

-

-

-

/ /

37 38 39 40 41 

POROSITY, IN PERCENT

42 43 44

FIGURE 15. Effect of surcharge packing on porosity.

surcharge and nonsurcharge techniques, ranges between 39.2 and 40.0 

percent. The use of the surcharge technique was accordingly considered unnecessary to obtain 'uniform packing.

EFFECT OF AMPLITUDE ON POROSITY

The effect of amplitude on porosity was determined over a range 

from 0.05 to 0.17 cm. Figure 16 shows that the effect of amplitude 

on porosity is small over the range of amplitude tested. The porosity 

again ranged between 39.2 and 40.0 percent.
A26 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

^ ^ 

0.18

0.17 -

0.16 -

0.15 -

0.14 -

co 0.13 

cc

"= 0.12 -

LJ

o

Q

0.11 -

0.10 -

0.09 -

0.08 -

0.07 -

0.06 -

0.05 -

s

( \

"C^f ' 1

0 36 37 38 39 40 41 42 43 44

POROSITY, IN PERCENT 

FIGURE 16. Effect of amplitude on porosity.

The packing research discussed previously suggested that a packing 

amplitude could be arbitrarily selected for small columns of glass 

beads. A shorter period of packing may be desirable however, because 

a lesser amount of sorting may result. Again, working under the 

same conditions as before, the porosity was determined over a 1- to
SPECIFIC YIELD A27

11

10

o 

o

Ld 7

if)

Od 

CO

> 5

O

Ld

i 4

//

0 36 37 38 39 40 41 42 43 44

POROSITY, IN PERCENT 

FIGURE 17. Effect of vibration on porosity.

10-second period of packing at a rheostat setting of B (0.09-cm amplitude). The results (fig. 17) indicate that the values of porosity 

were somewhat erratic over the range of 1 to 4 seconds total time 

of vibration but seemed to stabilize and give reproducible results at 

a porosity of approximately 39.3 for vibration periods of 5 seconds 

or longer. The porosity was similar to that obtained when the longer 

period of vibration was used. From the results of this study, a 

technique using the Syntron packer for small volumes of glass beads 

was standardized at 10 seconds vibrations and a rheostat setting of 

B (0.09-cm amplitude).

690-146 0 63 5
A28 HYDROLOGIC PROPERTIES OF EARTH MATERIALS 

PACKING OF LONG COLUMNS

The drainage research necessitated the use of 60-inch segmented 

columns of porous media. The small-volume technique therefore 

needed to be projected into this work to test its application. To do 

this, duplicate columns of taped segments were filled with 0.120-mm 

glass beads and were packed for 10 seconds using the si ort-column 

technique. After vibration, the columns were segmented and porosities determined for the individual segments. Figure IP shows the 

distribution of porosity vertically throughout a 1-inch segmented 

column. The porosity ranged from about 38 to 40 percert and averaged about 39 percent, a value slightly less than that obtained when 

the technique was applied to small volumes. There was, however, no 

consistent increase or decrease in porosity throughout the column, and 

the vertical reproducibility was good. To test this technhue further 

and improve it, duplicate segmented columns held together by a pressure brace were filled with 20-mesh Del Monte sand, and the former 

testing conditions were duplicated. Figure 19 shows the range of 

porosity after drainage for duplicate runs and shows, as before, that 

vertical distribution of porosity was reproducible and no consistent 

trend away from the average porosity. The above technique of packing was therefore considered to be applicable to long- as well as shortcolumn packing and was used as a standard method for all future 

packing.

EFFECT OF PACKING ON SORTING

To study the amount of sorting caused by packing, a 2?4-cc cylindrical container was filled approximately two-thirds full with two 

layers of glass beads; the lower layer was composed of colored glass 

beads 0.120-mm in diameter, and an upper layer was composed of 

uncolored glass beads 0.036 mm in diameter. During the first 5 seconds, the interface between layers shifted slightly downward along 

one edge, and the interface became more irregular on the downward 

side, an interpenetration of about 0.3 cm occurring on this side. As 

the vibrational interval was increased to about 10 seconds, the down- 

\vard shift of the interface increased and the downward side of the 

interface became even more irregular. The maximum interpenetration was approximately 0.7 cm.

As an additional means of evaluating the sorting qualitatively, a 

4-foot column, 1% inches in diameter, was filled with a mixture of 

colored 0.120-mm glass beads and uncolored 0.036-mm glass beads 

and vibrated for a 300-second interval at an amplitude of 0.03 cm. 

During the first 10 seconds, the only noticeable sorting occurred in 

the upper quarter of an inch of material. As the total time of vibra-
SPECIFIC YIELD A29

65 

60 

55

50

C/3

UJ

1 45

Z

Zf 40 

S 

=) 

_i 

O 

0 35

u_ 

0

UJ

< 30

CD 

UJ

O 25 

CD

h0 20 

UJ

X 

15

10 

5

0 

(

 ** 

 ?> 

%

\

;

.

.*

*

^*

I

0

*

0.

i

*

,

vv

) 20 30 40 50 6

POROSITY, IN PERCENT 

FIGURE 18. Distribution of porosity in a long column of 0.120-mm glass beads.

tion increased, the circulation and sorting increased in the upper part 

of the column, and at the end of 150 seconds there was definite stratification in the top 6 inches of the glass beads. After 300 seconds of 

vibration, the upper 8 inches of glass beads showed obvious layering; 

the central section of the column of beads showed vague stratification, 

and the lower part still showed no noticeable sorting.
A30 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

50

45

(/)

LUI 40

O

z

z

o

0

LU

0 30

LU

CD

LU

CO

(3 on

LU 2°

X

15

10

5

o

 o

 0

 o

.

0

,0

o

0

s

0

o

 0

0«

m

9

o

 0

 0

«

 0

0*

 0

o

o

EXPLANATION

o

Column 2

0 10 20 30 40 50 6C 70 

POROSITY, IN PERCENT

FIGURE 19. Distribution of porosity in long columns of 20-mesh Del Monte sand.

To investigate more fully the effect of vibration on sorting throughout the length of a 4-foot column, 1-inch layers of colored glass beads 

of 0.120-mm diameter were placed with the base of the layer at 9, 17,
SPECIFIC YIELD A31

Surface.

45 (

O 20 

00

^Original position of base of layer

0 50 100 150 200 250 300

TOTAL TIME OF VIBRATION, IN SECONDS 

FIGURE 20. Settling throughout a long column of glass beads.

25, 33, 41, and 45 inches above the base of the column, separated by 

uncolored 0.036-mm glass beads. The migration of these layers was 

then observed during vibration. Figure 20 shows the relative settling 

throughout the column for total time of vibration from 0 to 300 seconds. The width of the cross-hatched bars shows the amount of
A32 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

settling that occurred. Because the uppermost layers would be more 

greatly affected by the total volume change, the bars become progressively wider toward the top of the column. The zone of interpenetration below each interface, along with this increase in settling, 

initially thickens toward the top of the column and migrates progressively downward with increasing total time of vibration. Because 

the amount of sorting was negligible for short periods cf vibration, 

the previously established standard of 10-seconds vibration was concluded to be valid.

EFFECT OF DYE ON DRAINAGE

The results of the column drainage in which a solution of fluorescein 

dye in water was used as the wetting fluid, as compared to de-aired 

water, are shown in figures 21 and 22. The 50-inch columns, iy2 

inches in diameter, were manually packed with 0.120-mm glass beads. 

Two of the three columns were wetted with dye, and the other was 

wetted with de-aired water. The one-wetting method was used, allowing periods of about 76 hours, with the head maintained at the top 

of the columns. The rate of discharge was determined during drainage periods of as much as 22 hours. The columns were then disassembled, and the moisture content retained after drainage was 

determined for the sections of the column. The rate of drainage and 

pattern of moisture distribution after drainage was very similar for 

both the fluorescein solution and the de-aired water. Although an 

increase in yield per unit of time occurred, possibly due to the wetting 

effect of the dye, more data should be obtained if dye is to be used for 

future testing because it is possible that the increase is within the 

limits of repeatability between drainage runs using the same material. 

The content retained after drainage agreed within about 1 percent 

for the two different fluids, which also is within the rang^, of repeatability between runs.

EFFECT OF TIME ON DRAINAGE

When an air-water interface is maintained during drainage, discharge continues at a gradually decreasing rate until the unsaturated 

permeability becomes extremely low and drainage finally ceases. Consequently, knowledge of the length of time of drainage is essential in 

the analysis of specific-yield data.

The effect of time on drainage for the alluvial-sane1 sample is 

shown in the drainage curve in figure 23. The decrease in rate of 

discharge with increasing time of drainage is emphasized by noting 

that the quantity of discharge increased only about 4 percent between 

6 and 70 hours of drainage. In addition, the previous- discussion
200

160

Q

LU

o: 

Q

en

Columns conta

dye solution

Column 2

x 

Column containing de-aired water

10 12 14 

ELAPSED TIME, IN HOURS 

FIGURE 21. Effect of fluorescein dye on quantity of water drained fr
A34 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

48

44

40

36

32

28

O 

O

O 24

20 O 

CO

I

<5 16

LJI

12

EXPLANATION

O

Column l

 

Column 2

x

Column containing de-aired water

Columns containing 

dye solution

0 4 8 12 16 20 24 26 

MOISTURE CONTENT, IN PERCENT BY WEIGHT

FIGURE 22. Effect of fluorescein dye on moisture retained after 

drainage of 0.120-mm glass beads.

indicated that drainage after 70 hours was by no mears complete, 

because the other methods of determination obtained quantities at 

least twice that determined after 70 hours.
SPECIFIC YIELD ASS

Hanging-water-column method

0 6 12 18 24 30 36 42 48 54 60 66 72 

ELAPSED TIME, IN HOURS

FIGURE 23. Effect of time on drainage from an alluvial sand.

INVESTIGATION OF THE CENTRIFUGE MOISTURE

CONTENT

The American Society for Testing Materials (1958, p. 12) has defined centrifuge moisture equivalent as "the water content retained by 

a soil which has been first saturated with water and then subjected to 

a force equal to one thousand times the force of gravity for one hour." 

It normally is expressed as a percentage by weight. The test reported 

in this study was designed to evaluate the centrifuge-moistureequivalent test as a laboratory method for estimating specif"? retention. Consequently, the research work involved the centrifuge moisture equivalent, but was not limited by the scope of the d°finition 

because many factors, such as the force times gravity and the length of 

time of centrifuging, were changed in the tests. The term "centrifuge 

moisture equivalent" is used in this report only when the standard 

centrifuge test was used. If the standard test was modified in any 

way, the resulting values are reported as "centrifuge moisture 

contents."

TECHNIQUE

MATERIALS

As shown in table 5, materials covering a wide range of centrifuge 

moisture equivalents were selected for study. These materials included glass beads of 0.036-, 0.120-, and 0.47-mm diameter; Del Monte 

sand in 20-, 30-, and 60-mesh sizes; loess obtained from near Trenton, 

Nebr., and Bonny Dam, Colo.; fuller's earth (200-mesh Western
A36 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

Clay Minerals Co., Ivy, Utah) ; kaolin (EPK Edgar Plastic Kaolin 

Co.. Edgar, Fla.), and N.F. national fine colloidal, powdered, No. 

5645 (Mine & Smelter Supply Co., Denver, Colo.). f;£!arefully selected 

alluvial materials from field sites near Fresno, Calif., and along the 

Arkansas River in Arkansas and Oklahoma also were used. Table 1 

presents particle-size distribution data for all samples.

TABLE 5. Centrifuge moisture equivalents of selected materials

Material

0.120-mm.. . .....................

60-mesh. ..........................

59CAL191/244. ................ _ .....

Glass beads: 0.036-mm.... ____ ....

67CAL122...... .......................

57CAL66 __ ....... __ .. __ ---.

57CAL110 _ ------ __ -------------

57CAL118 -- _- -

59CAL268-261... ......... -.....- __ ..

59CAL251-252 ........ __ ..........

59CAL253-254 ............... .......

59CAL137-138 --------------- ___ -

57CAL72.... .............. _ .........

580KL15. ...... ....................

Centrifuge 

moisture 

equivalent

0.4

.5

1.2

1.3

1.4

1.9

3.4

4.0

4.2

5.4

6.0

'9.8

i 10.6

112.4

'13.2

14.1

M6.5

17.3

Material

57CAL106.. ..- ......- --...--

59CAL248 .......................

580KL42..- ........................

57CAL155 - _ ..... ___ ...........

59CAL130-131.-. ...... ... .......... ..

57CAL139.... ......--. ............

57CAL152 . __ ........-----------..

57CAL162-.-.. _ ........ _ ..........

57CAL173--.. ..-..----.- _ ..... _ .-

58ARK146. ........ ...-. ... .... ...

57CAL112 -- ......- - 

57CAL123 . -- .

57CAL2... .................... ........

57CAL205.-.. ___ ... ___ ...... __ .

Kaolin (N.F.). ...... ..................

Kaolin (EPK)........................

Centrifuge 

moisture 

equivalent

17.6

19.0

120.2

220.4

21.6

123.1

24.8

28.8

30.0

32.3

237.2

40.9

43.2

46.4

49.3

49.6

61.2

109.0

3 120. 0

1 Cenrifuged for a period of 2 hr.

2 Centrifuged for a period of 3.5 hr.

a Water was standing on sample after eentrifuging.

PROCEDURES

Centrifuge moisture equivalents are determined by several techniques in scientific laboratories throughout the United States. The 

principal difference in the technique is in the type of ccntainer and 

the size of samples that are used. Two types of containers are generally used the moisture-equivalent box and the Gooch crucible, in 

which 30 and 5 grams of soil are placed, respectively. The Hydrologic Laboratory normally uses the Gooch crucible method, details of 

which are as follows:

1. A 5-gram sample is placed on a filter paper at the bottom of a 

Gooch crucible iy2 inches high, about 27 milliliters in volume, and 

perforated at the bottom to allow the free discharge of water. 

(See fig. 24.)

2. The crucible is placed i,n a pan, and water is added to tlx °, pan to the 

level of the top of the sample. The sample is allowed to saturate 

from below for at least 16 hours.

o. The crucible-is placed in a humidifier, and the sample is allowed to 

drain for at least 4 hours.
SPECIFIC YIELD

^1^^

A. Gooch crucible and trunnion cup.

B. Moisture-equivalent head and boxes. 

FIGURE 24. Centrifuge equipment for crucible and box methods.

4. The crucible is placed in the centrifuge and rotated at a force of 

1,000 times gravity (at the center of gravity of the sample) for 

1 hour.

5. The sample is transferred to a moisture can and weighed.

6. The moisture can containing the sample is placed in a drying oven, 

and the sample is dried at least 16 hours at a temperature of 

110°C.

7. The moisture can containing the soil sample is placed in a desiccator 

to cool and then reweighed.

8. The moisture equivalent is expressed as the moisture'content, in 

percentage by dry weight, and is calculated as follows:
A38 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

w w w w'-ife!drxioo-i£xiflo

where

w=moisture content, in percentage by dry weight 

W7u,sc=weiglit of wet sample and container after centrifuging, in

grains

Wsc= weight of dry sample and container, in grams 

Wc=weight of container, in grams 

Ww=weight of water, in grams 

1^=weight of dry sample, in grams.

This procedure was used as standard in the experiments evaluating 

the centrifuge-moisture-equivalent test. Usually only one of the factors affecting the test was changed in any one experiment. A controlled-temperature centrifuge was used, except where data on the 

uncontrolled-temperature centrifuge were obtained for comparison. 

The temperature of the controlled-temperature centrifuge was maintained at 20°C, except in experiments where the effect of temperature 

on the centrifuge moisture content \vas being evaluated. A thin film 

of water was placed at the bottom of the controlled-temperature centrifuge chamber to assure a high relative humidity during centrifuging. In most of the experiments 5-gram samples in the smaller 

crucibles were used, and tests were made in duplicate. Soil samples 

were prepared through a No. 10 sieve (2 mm). When larger samples 

were needed, Gooch crucibles having a height of 3 inches and a volume 

of 125 ml were used.

The procedure for thp moisture-equivalent box method was nearly 

the same as for the crucible method, except 30-g samples were used; 

and square metal boxes, rather than crucibles, were used to hold the 

samples.

FILTER PAPER

Judging from evaluation tests, the retentivity of the filter paper 

did not seem to have any consistent effect on the centrifuge moisture 

equivalent.

The wet strength of the filter paper, however, was found to be a 

factor to be considered in the selection of a filter paper. For example, 

most papers tore when an attempt was made to remove them from the 

kaolin samples.

Whatman filter paper 540 (factory-cut to crucible size) was selected 

for use in the smaller crucibles. Whatman filter paper 50 was selected 

for use in the larger crucibles.

DUMMY COLUMN

The dummy column provides an extended water column beneath the 

sample. Thus, a lower force times gravity may be used to obtain a
SPECIFIC YIELD A39

desired average moisture tension in the sample, and, in addition, the 

range in moisture tension from the top to the bottom of the sample may 

be reduced. Porvic a semipermeable plastic sheet, 0.8 mm thick 

was selected as the material for use as a dummy column. The column 

was prepared by cutting a cross-shaped porvic strip in the configuration shown in D of figure 25. The strip was folded so that the four

FIGURE 25. Large-size dummy column and accessory centrifuge equipment. A, trunnion 

cup and crucible holder. B, assembled dummy column with plastic sample ring. C, 

Gooch crucible. D, porvic strip. E, plastic disk cemented on plastic cylinder. F, 

plastic cylinder for holding porvic strip in place.

arms extended downward from a circular center. The center of the 

strip was then placed over a plastic disk cemented to one end of a 

plastic cylinder (E}. The triangular ends of each arm were held in 

place by inserting a small plastic cylinder (F), cut to give spring 

action, inside the first cylinder. This assembly then fitted snugly in 

a Gooch crucible. The length of the porvic column was 2 cm in the 

small crucibles and 5 cm in the large crucibles. Air was purged from 

the porvic by placing it in warm water and applying vacuum for 1 

hour.

In one procedure, 5- and 15-gram samples were placed over the 2- 

and 5-cm columns, respectively, giving samples of similar thickness 

in the two sizes of crucibles. A force times gravity that w^ould give a 

tension of 500 cm of water at the bottom of the sample was applied 

in the centrifuge. This is the approximate tension at the center of 

gravity of coarse- and medium-textured materials when centrifuged
A40 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

at 1,000 times the force of gravity. A force of 250 times gravity for 

the 2-cm dummy column and a force of 100 times gravity for the 5-cm 

dummy column were used to give a tension of 500 cm of water at the 

bottom of the sample.

In another procedure, values of centrifuge moisture content at a 

tension of 345 cm of water (i/£ atmosphere) for undisturbed and disturbed materials were obtained by placing a 1-cm-thick sample on a 

5-cm porvic strip and centrifuging at a speed that would apply a 

tension of 345 cm of water (ys atmosphere) at the center of gravity 

of the sample.

DISCUSSION OF CENTRIFUGE DATA 

COMPARISON OF CRUCIBLE AND BOX METHODS

Moisture equivalents obtained in the controlled-temperature centrifuge, using both the Gooch crucibles and the moisture-equivalent 

boxes, are given in table 6.

TABLE 6. Moisture equivalents obtained by crucible and box methods

Material

Del Monte sand: 

20 mesh ______ __ . __ ____ _ _ __ _ __

60 mesh _

Glass beads (0.120 mm)

5f AL191/244__ ___ ___ __ __ __ ___ _ __ __

Loess (Bonny Dam, Colo.) __

Centrifuge moisture 

equivalent (percent)

Gooch 

crucible

0.5 

1. 4 

1.3 

1.9 

17.3

Moistureequivalent 

box 

method

0.6 

1. 6 

1.9 

2. 2 

17.3

EFFECT OF TEMPERATURE IN THE CONTROXiLED-TEMPERATTIRE

CENTRIFUGE

The effect of changing the temperature in the chamber of the controlled-temperature centrifuge on the centrifuge moisture content was 

studied for 12 materials covering a wide range of particle-size distribution. All materials were centrifuged over a range from 5° to 

30°C for 1 hour except kaolin and fuller's earth, which were centrifuged for 6 hours. The time of centrifuging was considered adequate 

for moisture equilibrium to be obtained. The effect of changing the 

temperature on the results of centrifuge moisture content is shown 

in figures 26 and 27. This illustration shows that there was a significant decrease in moisture content as temperature increased. The 

difference in moisture content between 10° and 30°C ranged from a
SPECIFIC YIELD A41

x

£ 3.0

O 2.5

1.5

1.0

°59CAL 191/244

30-mesh Del Monte sane

10 15 20 25 

TEMPERATURE, IN DEGREES CENTIGRADE

30 35

FIGURE 26. Effect of temperature In the controlled-temperature centrifuge on the centrifuge moisture content of coarse-textured materials.

fraction of 1 percent in the coarse-textured materials to 6 percent in 

some of the fine-textured materials. For the coarse-textured materials, 

the percentage change in moisture content over the range of 10° to 

30°C ranged from 13 to 34 percent, as compared to a range of 4 to 27 

percent for the fine-textured materials.

An increase in temperature could affect the moisture content of 

the sample by a decrease in surface tension of the pore water and an 

increase in evaporation from the sample. The relative humidity in 

the centrifuge chamber was measured and found to be near 100 per-
HYDROLOGIC PROPERTIES OF EARTH MATERIALS

0 5 10 15 20 25 30 35 

TEMPERATURE, IN DEGREES CENTIGRADE

FIGORE 27. Effect of temperature in the controlled-temperature centrifuge on the centrifuge moisture content of fine-textured materials.

cent throughout the period of centrifuging. Therefore, because evaporation from the sample was negligible, the decrease in moisture 

content seems to be due to a change in the surface tension of the 

water.

These tests indicated that temperature should be controlled at a 

preselected value. A temperature of 20° C was used as a standard in 

all later studies, except those dealing further with temperature 

eifects.
SPECIFIC YIELD A43

Uncontrolled-temperature centrifuge

O

Controlled-temperature centrifuge

23456 

TIME SINCE CENTRIFUGE STARTED, IN HOURS

FIGURE 28. Effect of length of period of centrifuge operation on the centrifuge moisture

content.

COMPARISON OF CONTROLLED- AN1> TTNCONTROL.LED-TEMPKRATURE

CENTRIFUGES

Samples were centrifuged for 1 hour each during a 7-hcur span 

of nearly continuous centrifuge operation to determine the effect of
A44 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

changes in prevailing conditions during the period of centrifuge 

operation. Results of the tests are shown graphically in figure 28. 

In these tests the centrifuges were operated almost continuously 

from the start of the experiment until the last group of samples was 

removed from the centrifuge. The only interruptions were those 

when the samples were being placed in, or removed from, the centrifuges. In the uncontrolled-temperature centrifuge, some samples 

were centrifuged during each hour of the 7-hour period. In the 

controlled-temperature centrifuge, samples were centrifuged only 

during the 1st, 3d, 5th, and 7th hours (the centrifuge was run empty 

during the other hours). A continuous record of the temperature 

and relative humidity in the chambers of both centrifuges w'as made.

The relative humidity ranged from 98 to 100 percent in the controlled-temperature centrifuge throughout the period of testing. The 

relative humidity in the uncontrolled-temperature centrifuge was 

close to 100 percent in the early minutes of each hour of testing and 

then decreased to the humidity of the room (which rarged from 32 

to 34 percent during the day). During the beginning period, the 

humidity in the centrifuge decreased to room humidity within half 

an hour. During each succeeding period of operation, however, relative humidity in the centrifuge decreased to room humidity in less 

than 5 minutes.

The temperature in the uncontrolled-temperature centrifuge was 

initially 27.8°C and increased progressively during succeeding hours 

of operation. After the first hour of operation, the temperature was 

38.3°C; after the second hour, 41.1°; and after the seventh hour, 

46.7°. The relation of this increase in temperature to the centrifuge 

moisture is shown in figure 29. Shown also is an extrapolation of 

the moisture-content temperature lines from figure 27, which were 

drawn from data obtained in the controlled-temperature centrifuge. 

The kaolin (EPK) data were not extrapolated because a centrifuging 

time of 6 hours was used for obtaining the data in figure 27. The 

centrifuge moisture content of the materials decreased linearly with 

increased temperature. The plotted values are somewhat below the 

extrapolated lines of the controlled-temperature data, supporting the 

conclusion that evaporation and surface tension are factors accounting for the decrease in moisture content with an increase in 

temperature.

The centrifuge moisture contents of the same materials tested in 

the controlled-temperature centrifuge at different times were nearly 

the same. The length of time the centrifuge had been in operation 

had little, if any, apparent influence on the centrifuge rioisture contents obtained. The data indicated also that temperature and humidity were accurately regulated in the temperature-controlled centrifuge.
SPECIFIC YIELD A45

60

50

40

30

20

10

I I 

EXPLANATION

Extrapolated lines from moisture contenttemperature data obtained in the 

con trolled-temperature centrifuge

39 41 43 45 

TEMPERATURE, IN DEGREES CENTIGRADE

47

FIGURE 29. Effect of temperature in the uncontrolled-temperature centrifuge on the 

centrifuge moisture content.

Results obtained in the uncontrolled-temperature centrifuge were 

very different from those obtained from the controlled. The centrifuge moisture content of the materials studied decreased as the 

length of time of centrifuge operation increased. After the centrifuge had been in operation for 7 hours, the centrifuge moisture content for 57CAL118 was about one-fifth of the value obtained when 

the centrifuge had been in operation for only 1 hour. Fc^ loess 

(Trenton, Nebr.) and 57CAL173, the centrifuge moisture contents 

after 7 hours of operation were about half the values obtained after 

1 hour of operation. For kaolin (EPK), the moisture content after 

7 hours of operation was about five-sixths of the 1-hour value.
A46 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

The difficulty in obtaining good duplication of results for samples 

run in the uncontrolled-temperature centrifuge has long been a matter 

of concern. Results from the present research indicate that the progressive heating of the uncontrolled-temperature centrifuge as the 

length of period of centrifuge operation is increased may be the 

explanation for this lack of duplication. The data shewn in figure 

28 indicate that repeatability of results is obtainable when samples 

are run at different times in the controlled-temperature centrifuge.

Another comparison of the controlled-temperature and uncont rolled-temperature centrifuges was made using 16 samples from the 

subsidence stud}^ area of California. The results are reported in 

table 7.

TABLE 7. Centrifuge moisture content obtained from the controlled- and uncontrolled-temperature centrifuges

Laboratory sample

57CAL66____ _ _________________________________

57CAL122__________ ____________-_---___-___--_

57CAL118___ _-_--- _____-_------_-__ ___ .-.

57CALllO---_____ ___-___-___-_--__---__-_____

57CAL72_________ _____________________________

57CAL139_____ -____--____-___--__-_-_---_-_ _-_

57CAL155_____--_-____-_--_-____-__- -_---_____

57CAL106_______ __________.___-_-_-_- _________

57CAL152 _ _________ _____

57CAL162 _________ _____

57CAL173 _ _ _______ _____

57CAL123_____ ______________.-_-_-_-_-_____-_-

57CAL2________ _______________________________

57CAL205 _ _ _

57CAL112______________ _______________________

57CAL14_. _-._ _ _________________

Uncontrolled-temperature centrifuge

Average 

centrifuge 

moisture 

equivalent 

(percent 

by weight)

1. 4 

1. 2 

3. 0 

1. 2

8. 0 

25. 5 

12. 4 

7. 4 

21. 1 

20. 2 

27. 2 

32. 8 

41. 4 

46. 9 

34. 6 

81. 9

Average 

centrifuge 

moisture 

equivalent 

multiplied 

by conversion ratio !

3. 0 

2. 7 

5. 1 

2. 7 

9. 7 

24. 0 

13. 1 

9. 2 

20. 5 

19. 8 

25. 3 

29. 2 

34. 8 

37. 5 

30. 4

Controlledtemperature 

centrifuge

Average 

centrifuge 

moisture 

equivalent 

(percent 

by weight)

4. 2 

4. 0 

6. 0 

5. 4 

14. 1 

24. 8 

21. 6 

17.6 

28. 8 

30. 0 

32. 3 

43. 2 

46. 4 

49. 3 

40. 9 

2 120. 0

1 See Piper (1933, p. 484).

- Water standing on sample after centrifuging included in moisture equivalent.

The samples are arranged in the table according to a decreasing 

content of sand. The average centrifuge moisture equivalent obtained 

in the uncontrolled-temperature centrifuge was multiplied by a ratio 

(Piper, 1933) used for converting centrifuge moisture-equivalent 

values to specific retention (by weight). It is not known at present 

whether a conversion ratio is necessary for centrifuge moisture contents obtained from the controlled-temperature equipment. If a con-
SPECIFIC YIELD A47

version ratio is necessary, it will be different from that used for the 

uncontrolled-temperature centrifuge and must be obtained from a 

comparison of centrifuge moisture contents with field and laboratory 

drainage data.

Except for sample 57CAL139, the moisture content after centrifuging was higher in the controlled-temperature centrifuge than in 

the uncontrolled-temperature centrifuge. For sandy materials, the 

moisture contents obtained from the controlled-temperature centrifuge were two or more times higher than those obtained in the 

uncontrolled-temperature centrifuge, whereas for the finer textured 

materials, the moisture contents obtained from the controlledtemperature centrifuge were of the magnitude of one- to two-tenths 

higher. These results seem reasonable because centrifuge moisture 

equivalents for sandy materials (usually obtained in an uncontrolledtemperature centrifuge) generally have been considered to-te lower 

than moisture contents obtained in the field. The moisture contents 

for the sandy materials obtained in the controlled-temperature centrifuge appear to be of the magnitude that would be expected in the 

field.

EFFECT OF LENGTH OF PERIOD OF CENTRIFUGING

The values of centrifuge moisture content obtained in the controlledtemperature centrifuge for the fine-textured samples from the subsidence area of California are somewhat higher than might be expected 

from field samples. In studies reported in the literature, r, period 

of centrifuging of 1 hour in the uncontrolled-temperature centrifuge 

was not considered adequate to allow the fine-textured materials to 

approach an equilibrium moisture content. Length of period of 

centrifuging, therefore, was considered in this study for the controlled-temperature centrifuge. The effect of the length of period of 

centrifuging on the centrifuge moisture content is shown graphically 

in figure 30 for six materials, two of which are from the California 

subsidence area. A centrifuge time of 6 hours was inadequate for 

moisture equilibrium to be approached for a fine-textured material, 

such as fuller's earth. The 0.036-mm glass beads required l°ss than 

1 hour to reach moisture equilibrium, whereas 1 to 2 hours were 

required for 57CAL2 and 2 to 4 hours for 57CAL14.

Data from this study indicate that 1 hour of centrifuging provides adequate time to approach moisture equilibrium in most coarseand medium-textured materials. However, for some materials, such 

as the fine-textured materials studied in this experiment, a centrifuge 

time in excess of 1 hour is necessary.

EFFECT OF APPLIED TENSION

Three methods of varying the tension applied to a sample during 

centrifuging were investigated in the controlled-temperature centri-
A48 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

140

100

1234567 

PERIOD OF CENTRIFUGING, IN HOURS

FIGURE 30. Effect of length of period of centrifuging in the controlled-temperature centrifuge on centrifuge moisture content.

fuge: changing the force times gravity, changing the thickness of 

the sample, and using dummy columns of different lengths below the 

sample.

If the influence of the filter paper below the soil samp^ on centrifuge moisture content is ignored, the soil-moisture tension at the 

periphery or bottom of the sample being centrifuged is considered to 

be zero. The soil-moisture tension at any distance from the bottom 

of the sample can be calculated from the equation (Eichards and 

Weaver, 1944) 
SPECIFIC YIELD A49

where

T= tension, in centimeters of water

co = angular velocity, in radians per second

g= acceleration of gravity, in centimeters per second per second

/'i = distance of bottom of sample from center of rotation, in

centimeters 

r2= distance of specified point in sample from center of rotation,

in centimeters.

If a force of 1,000 times the force of gravity is applied to a sample 

having a center of gravity 4 mm from the bottom of the sample, then, 

by the equation, the soil-moisture tensions at successive millimeter 

increments from the bottom to the top of the sample will be 101, 201, 

301, 400, 498, 596, 692, 789, 884, and 979 cm of water. Decreasing 

the force times gravity at which a sample is centrifuged would lower 

the soil-moisture tension at the center of gravity of the sample. Increasing the sample thickness would increase the soil-moisture tension 

at the center of gravity of the sample. The use of a porvic dummy 

column beneath the soil sample would also increase the soil-moisture 

tension at the center of gravity of the soil sample.

FORCE TIMES GRAVITY

Three homogeneous mixtures of glass beads (0.036, 0.120, and 0.470 

mm) and a loess (Bonny Dam, Colo.) were used in the study on the 

effect of changing the force times gravity. The effect of changing 

force times gravity on the centrifuge moisture content of thes^ materials is shown graphically in figure 31.

The height of the zone of capillary saturation, measured in the 

column-drainage study of glass beads (fig. 9), was about 72, 24, and 6 

inches for the 0.036-, 0.120-, and 0.470-mm beads, respectively. Dividing the height of the zone of capillary saturation by the sample thickness, which is approximately 0.32 inches, gives the calculated force 

required to start the sample to drain. The calculated values of force 

times gravity are 225 for the 0.036-mm beads, 75 for the 0.120-mm 

beads, and 19 for the 0.470-mm beads. The values of forc3 times 

gravity obtained by extrapolation (fig. 31) of the experimental data 

are about 235 for the 0.036-mm beads, 74 for the 0.120-mm beads, and 

15 for the 0.470-mm beads. These values agree closely with the 

calculated results, indicating that the given soil-moisture tension was 

reproduced by changing the force times gravity in the controlledtemperature centrifuge. Thus, by applying the proper force times 

gravity, the moisture content at a specified height within a centrifuge 

sample will be similar to that at a given height in the drainage column.

The curves in figure 31 illustrate that for homogeneous materials, 

such as glass beads, drainage occurs over a relatively narrow tension
A50 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

range; whereas for more heterogeneous materials, s^ch as loess, 

drainage occurs over a much wider tension range.

The study of the effect of changing the force times gravity was expanded to include medium- and fine-textured materials. These materials were centrifuged over a range of 1 to 2,000 time? the force of 

gravity. The results of the centrifuging are shown in figure 32. For

10 50 100

FORCE TIMES GRAVITY

FIGURE 31. Effect of force times gravity on centrifuge moisture contert for coarse- and

medinm-textured materials.

300 600 900 1200 1500 

FORCE TIMES GRAVITY

1800 2100

FIGURE 32. Effect of force times gravity on centrifuge moisture content for medium- and

fine-textured materials.
SPECIFIC YIELD A51

sample 57CAL118, the moisture content decreased rapidly as the low 

centrifugal forces were applied and decreased only slightly thereafter. 

Results with loess from Trenton, Nebr., were similar to those for loess 

from Bonny Dam, Colo., the moisture content decreasing at a decreasing rate as centrifugal force increased. The values of moisture content for kaolin (EPK) were similar for forces of 500 to 1,000, but 

they decreased about 10 percent between 1,000 and 2,000 times gravity. 

The values of moisture content for fuller's earth decreased continually 

up to a force of 500, remained about the same for forces of 500 to 

750, increased from 750 to 1,000, and then remained at the same level 

for forces from 1,000 to 2,000 times gravity. The increase above 750 

could be a result of an increased compression at the higher centrifugal 

forces and a resultant lower permeability.

SAMPLE THICKNESS

The effect of changing the sample thickness on the centrifuge 

moisture content required a study of the change in moisture content 

at different heights within a sample and a study of the moisture 

content for samples of different thicknesses. In these studies a force 

of 1,000 times gravity was applied.

The data on the centrifuge moisture content at different heights 

within samples of 0.120-mm glass beads and loess (Trenton, Nebr.) 

are illustrated in figure 33. The samples were about 2.1 cm thick 

and were segmented with a spatula at selected vertical increments 

from the top to the bottom of the samples. The moisture content was 

then determined for each increment. The centrifuge moisture content 

for the 0.120-mm glass beads was nearly the same for all measured 

increments, whereas the measured centrifuge moisture content of 

loess decreased with increased distance from the bottom of the sample.

The actual decrease in moisture content from bottom to top in the 

centrifuged sample may be more pronounced than is shown in figure 

33 because there probably was some redistribution of moisture upward after the centrifuge was turned off and before the sampling 

was completed. This fact is explained by the high-tension gradient 

between the top and bottom of the sample developed during centrifuging. If redistribution of moisture in the sample did not occur after 

centrifuging, the curves in figure 33 would represent a drained 

column of about 2,100 cm long. As discussed and illustrated previously in this report, the retained-moisture content of 0.120-mm glass 

beads would be similar over all but the lower part of such a column, 

whereas for loess, the moisture content would show a continual decrease with increased distance from the bottom of the column.

The centrifuge moisture content of different sample thicknesses of 

0.036-mm glass beads, loess (Trenton, Nebr.), kaolin (EPF), and 

fuller's earth is shown graphically in figure 34. The centrifuge mois-
A52 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

ture content of 0.036-mm glass beads and loess decreased, at a decreasing rate, as the sample thickness increased. This is to be expected 

because the soil-moisture tension at the center of gravity of a sample 

is increased with increased thickness of sample, and the moisture 

content should, therefore, decrease. However, the results for kaolin 

(EPK) and fuller's earth did not follow the expected trend because 

moisture content increased as the sample thickness increased. Tests 

were made on samples of kaolin (EPK) and fuller's earth 3 cm thick 

to determine if this discrepancy might be due to the low permeability 

of the materials. Table 8 provides a comparison between the values 

of moisture content obtained after 1 and 4 hours of centrifuging and 

after 1 hour of centrifuging followed by 1 hour of storage in the 

centrifuge chamber.

0.120-mm glass beads Loess (Trenton, Nebr.)

0 2 4 6 8 10 12 14 16 18 20 22 

CENTRIFUGE MOISTURE CONTENT, IN PERCENT BY WEIGHT

FIGURE 33. Moisture content at different heights within samples aft^r centrifuging.

TABLE 8. Moisture content after centrifuging samples of fine-textv.red materials, 3

cm thick

Average centrifuge mo'sture content 

(percent by weight)

Centrifuging (hours)

1 .

4

Fuller's earth

Water 

standing 

on sample 

excluded

108. 5 

129. 4 

104. 3

Water 

standing 

on sample 

included

140. 3 

142. 1 

104. 3

Kaolin (EPK)

Water 

standing 

on sample 

excluded

f 5. 8 

63. 7 

54. 2

Water 

standing 

on sample 

included

87. 6 

85. 8 

64. 5

1-hr storage in centrifuge.
SPECIFIC YIELD A53

150

1234 

SAMPLE THICKNESS, IN CENTIMETERS 

FIGURE 34. Effect of sample thickness on centrifuge moisture content.

When water was found standing on the samples after the test, two 

calculations of moisture content were made one excluding the water 

standing on the sample and the other including it. When th°- water 

on top of the samples after centrifuging was excluded, the values of
A54 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

centrifuge moisture content obtained after 1 and 4 hours of centrifuging were virtually the same. However, when the water standing 

on the sample was included, the values of centrifuge moisture content 

after 1 hour were 35 percent higher for fuller's earth ard 36 percent 

higher for kaolin than after 4 hours of centrifuging. These data indicate that a period of centrif uging considerably in excess of 1 hour 

would be required to obtain moisture equilibrium in the 3-cm-thick 

sample.

AVhen the water standing on the sample was included, the values of 

centrif uging moisture content obtained after 1 hour of centrif uging 

were not appreciably different from those obtained after 1 hour of 

centrifuging followed by 1 hour of storage in the centrif ige chamber. 

However, when the water standing on the sample was excluded, the 

centrifuge moisture content after the 1-hour storage period was 22 

percent higher for fuller's earth and .-14 percent higher for kaolin than 

after 1 hour of centrifuging and no storage. This may indicate that 

the samples were compressed during centrifuging and tl at, after the 

force was released, the samples expanded and absorbed some of the 

water standing on the sample.

Changing the soil-moisture tension by altering the thickness of the 

sample apparently has certain practical limitations when materials of 

low permeability are used. Increasing the thickness of the sample 

would result in a lower permeability because the increased weight 

would produce greater sample density. This decreased permeability, 

along with a longer drainage column, wT ould necessitate an appreciable 

increase in the length of time of centrifuging to obtain moisture 

equilibrium.

This research emphasizes that duplication and reliability in the 

centrifuge-moisture-equivalent test are possible when the sample is 

accurately weighed (comparable thicknesses are obtained) and when 

the total thickness of sample is used.

DUMMY COLUMN

The values of centrifuge moisture content for 10 samples, using 2- 

and 5-cm dummy columns, are shown graphically in figure 35 with 

data obtained by the standard technique. Except for the fine-textured 

materials, fairly close agreement in centrifuge moisture content was 

obtained by the three methods. For fine-textured materials, the centrifuge moisture equivalent was somewhat higher than the values of 

centrifuge moisture content obtained by use of porvic dummy columns.

The effect of the length of time of centrifuging on the centrifuge 

moisture content of samples placed on a 2-cm porvic dummy column 

is illustrated in figure 36. The moisture content for sample 57CAL173 

was nearly constant throughout the test, whereas the moisture content
SPECIFIC YIELD A55

for the other three samples decreased slightly between 1 and £ hours 

but remained about the same after 2 and 4 hours of centrifuging. 

Data in figure 30 illustrate that sample 57CAL14 required about 2 

hours of additional centrifuging to obtain moisture equilibrium when 

the porvic dummy column was not used. Because of the shape of the 

Gooch crucible, a 5-gram sample placed at the bottom of the crucible 

is about twice as thick as a 5-gram sample placed over a 2-cm porvic 

dummy column. The thinner sample and the resultant decrease in 

compaction are possible explanations for the shorter period of time 

required to approach moisture equilibrium when using the porvicdummy-column method.

Although the use of a porvic dummy column adds another step to 

the centrifuge procedure, it has certain advantages over the conventional procedure. Use of the porvic dummy permits a reduction in the 

range of moisture tension from the top to the bottom of the sample, a 

reduction in the force times gravity required to obtain a specif ed tension on the sample, and a reduction in the length of period of centrifuging required to approach moisture equilibrium.

COMPARISON OF DISTURBED AND UNDISTURBED &T*ES

A comparison of centrifuge moisture values at ^-atmosphere tension for undisturbed and disturbed samples is given in table 9 for 9 

materials. The undisturbed1 and disturbed centrifuge moisture contents were within 1.1 percent for 5 of the materials. For the other 4

I^U

110

1-

I 100

o

LU

5 90

CD

£ 8°

§ 70

Lt

LLl

°- 60

Z

H 50

Z

LLl £ 40

o 

o

LU 3°

Lt

? 20 

CO

O

2 10

EXPLANATION

D

Force 1000 t mes gravity

Cenlr fuge moisl re

r.vvi E/3

equivalent

Centrifuge mo sture

content

Force 250 times gravity _

2-c ntimeter porv

1

c column £

LJ

c

m -^

^ Force 100 times gravity m §, %

2 5-c 

o 

U

E

Q

 0 T3 C

_ ro ro c

0)0) O

-Q n 00 

- n n "i

 T 00 0)

Ofl Ofl O

E E ^ ~* 

E E < 

o ^> 1 ^^^B

CM CO ^1 ^^1

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endmefer p

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o

c

0)

£

01

o

1

< 3

U |V

-J 1 II 3 -1

in

^^^1

1

JK.

-

^.

^ ~

U

fv 

in

-

_

-

-

FIGURE 35. Centrifuge moisture equivalent compared with centrifuge moisture content

obtained with porvic dummy columns.
A56 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

1 

0

LU

^ 70

>

00

1-

z

UJ

O

Q_

UJ Q_ Kn

z

iz

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0 50

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30

k

^,

It-^

^

^, ;

> <

57 CAL 14

57 CAL 123 j

57 CAL 205

57 CAL 173

T

01 

TIME, 

2345

IN HOURS

FIGURE 36. Effect of length of time of centrifuging on the centrifuge rioisture content 

of samples placed on a 2-cm porvic dummy column.

TABLE 9. Comparison of centrifuge moisture values at one-third atmosphere tension 

for disturbed and undisturbed samples

Soil

59CAL253-254__---_-_____-_-______-____--__------_

59CAL251-252. ____________________________________

59CAL258-261__-------_-___ ___----_-----_----_-___

59CAL137-138_------_._ ______-_---_-_-_-_--__-____

580KLA42____ _____________________________________

58OKLA15____ _____________________________________

59CAL248---- __------__. ______________________

59CAL130-131-___---____-.-.__-_--_-_-_-___--.____

58ARK146 _------__---_______---__-----_--__---__

Undisturbed 

sample

11. 0

13. 1

13. 6

15. 1

18. 8

20. 1

20. 6

21. 9

29. 4

Disturbed 

sample '

14. 6

13. 6

13. 0

14. 4

23. 4

19. 0

20. 6

25. 9

33. 6

Centrifuge' moisture content

Disturbed samples prepared through a No. 10 (2 mm) sieve.
SPECIFIC YIELD A57

materials the undisturbed centrifuge moisture content ranged from 

3.6 to 4.6 percent lower than the centrifuge moisture contents of the 

disturbed samples.

SUMMARY AND CONCLUSIONS

The first 2 years of research on specific yield have been directed 

toward a review of the literature relating to this field and a study of 

the drainage and centrifuge moisture equivalent of porous media. An 

annotated bibliography (Johnson & others, 1960) presented the first 

phase of this study, and the present report summarizes the research 

completed on column drainage and centrifuge moisture equivalent.

INVESTIGATION OF COLUMN DRAINAGE

The principal testing materials used in this study were homogenous 

glass beads or Del Monte sand; however, carefully selected b'lt less 

homogenous sandy materials chiefly from field sites in California 

were also used. These materials were mechanically packed into continuous or transparent segmented plastic columns of 1- to 8-inch diameter. The material was wetted with Denver tap water and drained 

under controlled conditions of temperature and humidity.

The data on moisture retention in 0.120-mm glass beads obtained by 

3 methods of drainage (simple, extended-base, and nonmembrane) 

were comparable, except at the higher moisture contents. In another 

method, the membrane method, the values of retained water were 

similar to those obtained by the first 3 methods at 52 to 68 inches above 

the water table. The membrane method was the most convenient and 

workable for determining moisture retained in short drainage columns.

The total discharge of water from duplicate columns of OJ20-mm 

glass beads for the simple free-drainage and nonmembrane hmgingwater-column methods was similar, but the initial rate of discharge 

was higher for the hanging-water-column method.

The distribution of moisture after drainage of a natural alluvial 

sand was less uniform than that obtained by drainage of the more 

homogenous glass beads.

The drainage characteristics for glass beads were affected only 

slightly by cleaning with acid. It was concluded that the increase in 

cost and effort associated with the acid cleaning of porous media was 

not warranted.

The diameter of the column made little difference in the moisture 

distribution after drainage of mechanically packed 1-, 4-, and 8-inch 

diameter columns of 0.120-mm glass beads. It likewise maclQ. little 

difference in the larger column whether the moisture samples were 

taken near the side of the column or in the middle.
A58 HYDROLOGIC PROPERTIES OF EARTH MATERIALS

Four procedures for wetting the porous media a single wetting, 

flow-wetting, two wettings, and capillary-rise wetting gave similar 

results for the distribution of moisture after drainage and for the rate 

of discharge.

The line of wetting was sufficiently visible under white light when 

ordinary tap water was used; therefore, it was not necessary to use a 

dye solution and ultraviolet light. The effect of the dye on the drainage characteristics of the media was negligible.

The variation in porosity in all similarly packed drainage columns 

indicated that repeatability was not achieved by the manual method 

of packing. Therefore, a mechanical method of packing was developed 

to obtain consistent and reproducible porosity within the glass beads 

and sands. The variation of porosity (used as an index of packing 

efficiency) in similarly packed columns was close generally less than 

2 percent. Sorting was considered negligible for short packing 

intervals.

A knowledge of the effect of time on drainage is important to understand how it affects specific yield. A large percentage of the water is 

yielded during the first part of a drainage cycle, with the rate of 

drainage decreasing steadily with time.

INVESTIGATION OF CENTRIFUGE MOISTURE CONTENT

The materials used in this study cover a wide range of moistureequivalent values. They include glass beads, commercial sands, loess, 

fuller's earth, kaolin, and selected alluvial materials principally from 

field sites in California.

The procedure used to determine centrifuge moisture equivalent was 

the Gooch crucible method, using the controlled-temperature centrifuge. A modification of this technique involved the US3 of a plastic 

dummy column to reduce the force times gravity applied and the range 

in moisture tension from the top to the bottom of the sample.

A comparison of crucible and box methods of determining centrifuge moisture-equivalent data indicates that the value? obtained by 

the crucible method are slightly lower than those obtained by the box 

method.

Results of the study indicate that reproducible results are obtained 

only when both the temperature and humidity are controlled. Changing the temperature on the centrifuge produced a small but significant 

decrease in moisture content as the temperature increased. The difference in moisture content between 10° and 30°C ranged from 13 to 34 

percent of the moisture content at 10°C for the coarse-textured materials, as compared to a range of 4 to 27 percent for the fine-textured 

materials. The conclusion is reached that the temperature in the 

centrifuge should be at a preselected value.
SPECIFIC YIELD A50

Centrifuge moisture contents obtained from the controlled- and 

uncontrolled-temperature centrifuges were not comparable. For 

coarse-textured materials, the moisture contents obtained from the controlled-temperature centrifuge were of the magnitude of one- to twotenths higher. With the uncontrolled-temperature centrifuge, the 

centrifuge moisture content decreased as the length of time of centrifuge operation increased. This was due to temperature buildup and 

decrease in humidity in the centrifuge during operation. These tests 

emphasize the difficulty in obtaining good replication of results for 

samples run in the uncontrolled-temperature centrifuge.

Although a 1-hour period of centrifuging is probably adequate for 

coarse- and medium-textured materials to approach moisture equilibrium, a longer period should be considered for fine-textured materials.

The average moisture tension applied to a sample during centrifuging was altered by changing the thickness of the sample and th°, force 

times gravity applied to the sample and by pla9ing the sample over 

different lengths of semipermeable dummy columns. Increasing the 

thickness of the sample increases the average moisture tension applied, 

but it has practical limitations, especially for fine-textured materials, 

because it also increases the period of time required for the soil sample 

to approach moisture equilibrium. Changing the lengths of semipermeable dummy columns on which the samples were placed had 

certain advantages over changing the force times gravity by the usual 

centrifuge procedure. Use of dummy columns reduced considerably 

the range in moisture tension from the top to the bottom of the sample 

from that in the conventional centrifuge test. Use of the c'umrny 

column also permits a reduction in the force times gravity required to 

obtain a specified tension on the sample and a reduction in the length 

of period of centrifuging required to approach moisture equilibrium.

SELECTED REFERENCES

American Society for Testing Materials, 1958, Procedures for testing soils: 

Philadelphia, Pa., Am. Soc. Testing Materials, p. 12, April.

Briggs, L. J., and McLane, J. W., 1907, The moisture equivalent of sofls: U.S. 

Bur. Soils Bull. 45.

 1910, Moisture equivalent determinations and their application: Am. 

Soc. Agronomy Proc., v. 2, p. 138-147.

Briggs, L. J., and Shantz, H. L., 1912, The wilting coefficient for differert plants 

and its indirect determination: U.S. Bur. Plant Industry Bull. 23C.

Clark, W. O., 1916, Ground water for irrigation in the Morgan Hill ar?a, California : U.S. Geol. Survey Water-Supply Paper 400, p. 61-105.

Eckis, Rollin, and Gross, P. L. K., 1934, South Coastal basin investigation 

Geology and ground-water storage capacity of valley fill: California Div. 

Water Resources Bull. 45, 273 p.
AGO HYDROLOGIC PROPERTIES OF EARTH MATERIALS

Ellis, A. J., and Lee, C. H., 1919, Geology and ground water of the western part

of San Diego County, California: U.S. Geol. Survey Wate^-Supply Paper

446, 321 p. 

Hazen, Alien, 1891, Experiments upon the purification of sewage and water

at the Lawrence Experimental Station, Nov. 1, 1889 to Dec. c 1, 1891: Massachusetts State Board Health Pub. 34, p. 425-633, December. 

Israelson, O. W., 1918, Studies on capacities of soils for irrigation water and

a new method of determining volume weight: Jour. Agr. Research, v. 13,

p. 1^35. 

Johnson, A. I., Morris, D. A., and Prill, R. C., 1960, Specific yield of porous

media, an annotated bibliography: U.S. Geol. Survey open-file rept. 

King, F. H., 1898, Principals and conditions of the movement of ground water:

U.S. Geol. Survey 19th Ann. Rept., pt. 2, p. 85-93. 

Meinzer, O. E., 1923, Outline of ground-water hydrology, with definitions: U.S.

Geol. Survey Water-Supply Paper 494. 71 p. 

 1932, Outline of methods for estimating ground water supplies: U.S.

Geol. Survey Water-Supply Paper 638-C, p. 99-144. 

Piper, A. M., 1933, Notes on the relation between the moisture equivalent and

the specific retention of water-bearing materials: Am. Oeophys. Union

Trans., v. 14, p. 481-487. 

Richards, L. A., and Weaver, L. R., 1944, Moisture retention by some irrigated

soils as related to soil-moisture tension: Jour. Agr. Research, v. 69, no. 6,

p. 215-235.

U. S. Government Printing Office: 1992 - 342-445 (74127)