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/NBS building science series TA435 .U58 V149:1982 C.I NBS-PUB-C 1974

TA

435

U58

No. 149

1982

C^2

NBS BUILDING SCIENCE SERIES BSS 149

Thermal Behavior of

Fine-Grained Soils

U.S. DEPARTMENT OF COMMERCE • NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act ol Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (I) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

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physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

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Absolute Physical Quantities^ — Radiation Research — Chemical Physics —

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NBS BUILDING SCIENCE SERIES BSS 149 ""tmiT

^ I H 1

Thermal Behavior of Fine-Grained Soils

Lawrence A. Salomone

William D. Kovacs

Herbert Wechsler

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued November 1982
Library of Congress Catalog Card Number: 82-600636

National Bureau of Standards Building Science Series 149

Natl. Bur. Stand. (U.S.), Bldg. Sci. Ser. 149, 102 pages (Nov. 1982)

CODEN: BSSNBV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1982

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price $5.50
ABSTRACT

Laboratory thermal probe tests performed on an AASHTO standard reference

material (a silty clay) showed that thermal resistivity (°C»cra/watt) varies

with soil moisture content and dry density. The tests were performed to correlate soil thermal behavior with the limit states of fine-grained soils. Over

80 thermal resistivity measurements were made on specimens compacted to various

densities and moisture contents .

Results are presented which indicate that the optimum moisture content of soils

and the Atterberg Limits can be correlated with the thermal behavior of finegrained soils. It was found that the minimum thermal resistivity (i.e. the

critical moisture content) occurred at the optimum moisture content when the

soils were compacted using various compactive efforts. The critical moisture

content defines the knee of the thermal resistivity versus moisture content

c curve. When the soils were compacted using a compactive effort of 1.42 x 10'^ J/m-^ (2970 ft-lbs per cubic foot), the minimum thermal resistivity occurred

at the plastic limit of the AASHTO standard reference material. Also, indices are defined which allow comparison of the thermal behavior of fine-grained

soils .

Keywords: Atterberg limit tests; compaction; compaction tests; heat flow;

laboratory tests; soil moisture; soil tests; tests; thermal

conductivity; thermal resistivity.

COVER: Temperature contours beneath a house and around

underground electric transmission lines.

iii
TABLE OF CONTENTS

Page

ABSTRACT iii

LIST OF FIGURES vi

LIST OF TABLES vili

NOTATION X

1. INTRODUCTION 1 1.1 GENERAL 1 1.2 LIMITATIONS OF PRESENT PROCEDURES USED TO EVALUATE THERMAL

SOIL PROPERTIES 2

1.3 PURPOSE 3

1.4 SCOPE 3

2. LABORATORY TESTING 7

2.1 TEST INSTRUMENTATION 7 2.1.1 General 7 2.1.2 Thermal Probes 8

2.1.2.1 Line Heat Source Theory 8

2.1.3 EPRI Thermal Property Analyzer 9

2.2 DESCRIPTION OF AMRL REFERENCE SOIL 10

2.3 TEST PROCEDURE 10

2.3.1 General 10

2.3.2 Selection of Molding Moisture Content 11

2.3.3 Soil Preparation 11

2.3.4 Sample Preparation 12

2.3.5 Thermal Probe Tests 13

2.3.6 Moisture and Density Determinations 14

3. THEORETICAL CONSIDERATIONS AFFECTING THERMAL PERFORMANCE OF SOILS ... 19

3.1 GENERAL 19

3.2 PRIMARY FACTORS AFFECTING THE THERMAL RESISTIVITY OF SOILS 20

3.2.1 Soil Composition 20

3.2.2 Density 20

3.2.3 Moisture Content 21

3.3 ASSESSING THE ENGINEERING PROPERTIES OF SOILS 22

3.4 DETERMINING THE THERMAL BEHAVIOR OF SOILS 24

3.4.1 General 24

3.4.2 Approach 24

4. PRESENTATION AND DISCUSSION OF TEST RESULTS 31

4.1 General 31

4.2 Effect of Density 32

4.3 Effect of Moisture Content 34

4.4 Determination of Soil Thermal Behavior 35

4.5 Thermal Behavior of Other Fine-Gralned Soils 38

iv
TABLE OF CONTENTS (Continued)

Page

5. CONCLUSIONS AND RECOMMENDATIONS 65

5.1 CONCLUSIONS 65

5.2 RECOMMENDATIONS 66

6. ACKNOWLEDGMENTS 67

7. REFERENCES 69

8. APPENDIX A - TABULATION OF DATA A-1

V
LIST OF FIGURES

Page

Figure 1-1. A qualitative comparison of the differences in terminology

used by agronomists and geotechnical engineers 4

Figure 1-2. Correlation of thermal resistivity with the Atterberg

Limits 5

Figure 2-1. Sectional view of a laboratory thermal probe 16

Figure 2-2. Front-panel layout of EPRI Thermal Property Analyzer 17

Figure 3-1. The effect of soil moisture on the heat flow path 26

Figure 3-2. The effect of moisture content and dry density on the

thermal resistivity of soils 27

Figure 3-3. Soil moisture scale showing soil moisture terms used by

agronomists 28

Figure 3-4. Soil moisture scale showing soil moisture terms (Atterberg

Limits) used by geotechnical engineers for fine-grained

soils 29

Figure 3-5. Moisture content continuum showing the various states of

fine-grained soils and the generalized stress-strain

response 30

Figure 4-1. Variation of thermal resistivity with moisture content and

dry density for AMRL Reference Soil 41

Figure 4-2. Variation of thermal conductivity with dry density for

various values of moisture content 42

Figure 4-3. Variation of thermal resistivity with dry density for

moisture contents of 3 percent to 18-1/2 percent 43

Figure 4-4. Variation of thermal resistivity with dry density for

moisture contents of 21 percent to 50-1/2 percent 44

Figure 4-5. Variation of thermal conductivity with moisture content

for various values of dry density 45

Figure 4-6. Diagram of thermal cond uctivity for AMRL reference soil .... 46

Figure 4-7. Compaction curves for modified, standard, and S6 energies .. 47

Figure 4-8. Correlation of modified energy moisture - density curve with thermal resistivity - moisture content curve 48

vi
LIST OF FIGURES (continued)

Page

Figure 4-9. Correlation of Intermediate energy moisture - density

curve with thermal resistivity - moisture content

curve 49

Figure 4-10. Correlation of standard plus energy moisture - density

curve with thermal resistivity - moisture content curve 50

Figure 4-11. Correlation of standard energy moisture - density curve with thermal resistivity - moisture content curve 51

Figure 4-12. Correlation of S12 energy moisture - density curve with

thermal resistivity - moisture content curve 52

Figure 4-13. Correlation of S6 energy moisture - density curve with

thermal resistivity - moisture content curve 53

Figure 4-14. Correlation of S4 energy moisture - density curve with

thermal resistivity - moisture content curve 54

Figure 4-15. Variation of minimum thermal resistivity with compactlve

effort 55

Figure 4-16. Correlation of thermal resistivity and Atterberg Limit

test data using S6 compactlve effort 56

Figure 4-17. Thermal behavior of AMRL reference soil sample using S6

compactlve effort 57

Figure 4-18 Georgia clay thermal resistivity test data 58

Figure 4-19. Niagara clay thermal resistivity test data 59

Figure 4-20. Northway silt loam thermal resistivity test data

adjusted for dry density 60

Figure 4-21. Fairbanks silt loam thermal resistivity test data

adjusted for dry density 61

Figure 4-22. Fairbanks sllty clay loam thermal resistivity test data

adjusted for dry density 62

Figure 4-23. Healy clay thermal resistivity test data adjusted for

dry density 63

Figure 4-24. Ramsey sandy loam thermal resistivity test data adjusted

for dry density 64

vii
LIST OF TABLES

Page

Table 2-1. Summary of Index Property Test Data, AMRL Soil Reference

Sample No. 61 11

Table 2-2. Summary of Compactive Efforts Used During Laboratory

Testing Program 13

Table 3-1. Textural and Other Characteristics of Soils 23

Table 4-1. Thermal Conductivity - Density Relationships 33

Table 4-2. Thermal Conductivity - Moisture Content Relationships 34

Table 4-3. Thermal Performance P^egions of AMRL Reference Soil 37

Table 4-4. Thermal Stability Index for AMRL Reference Soil 38

Table 4-5. Correlation of Critical Moisture Content and Optimum

Moisture Content for Other Fine-Grained Soils 39

Table 4-6. Correlation of Critical Moisture Content and Plastic

Limit for Other Fine-Grained Soils 40

Table A-1 . Summary of Laboratory Test Data, Modified Compaction

Energy A-2

Table A-2. Summary of Laboratory Test Data, Intermediate Compaction

Energy A-3

Table A-3. Summary of Laboratory Test Data, Standard Plus Compaction

Energy A-4

Table A-4. Summary of Laboratory Test Data, Standard Compaction

Energy A-5

Table A-5. Summary of Laboratory Test Data, S12 Compaction Energy A-6

Table A-6. Summary of Laboratory Test Data, S6 Compaction Energy A-7

Table A-7. Summary of Laboratory Test Data, S4 Compaction Energy A-8

Table A-8. Computed Values for the Zero Air Voids Curve for

Gg = 2.76 (100% Saturation) A-9

Table A-9. Summary of Moisture Content Data, Modified Compaction

Energy A-10

Table A-10. Summary of Moisture Content Data, Intermediate

Compaction Energy A-10

viii
LIST OF TABLES (continued)

Page

Table -A-11. Sununary of Moisture Content Data, Standard Plus

Compaction Energy A-11

Table A-12. Summary of Moisture Content Data, Standard Compaction

Energy A-11

Table A-13. Summary of Moisture Content Data, S12 Compaction Energy .... A-12

Table A-14. Summary of Moisture Content Data, S6 Compaction Energy A-13

Table A-15. Summary of Moisture Content Data, S4 Compaction Energy A-14

Table A-16. Moisture Loss (Gain) of the Test Samples During the

Thermal Probe Test, Modified Compaction Energy A-15

Table A-17. Moisture Loss (Gain) of the Test Samples During the

Thermal Probe Test, Intermediate Compaction Energy A-16

Table A-18. Moisture Loss of the Test Samples During the Thermal

Probe Test, Standard Plus Compaction Energy A-16

Table A-19. Moisture Loss (Gain) of the Test Samples During the

Thermal Probe Test, Standard Compaction Energy A-17

Table A-20. Moisture Loss of the Test Samples During the Thermal

Probe Test, S12 Compaction Energy A-17

Table A-21. Moisture Loss (Gain) of the Test Samples During the

Thermal Probe Test, S6 Compaction Energy A-18

Table A-22. Moisture Loss of the Test Samples During the Thermal

Probe Test, S4 Compaction Energy A-19

ix
NOTA.TION

A,B = soil constants in eq. 9

A]_ = the slope of the line, equation 10

B]^ = the value of the intercept of the curve at 1 percent moisture

Ei = designation for exponential integral (eq. 2)

k = thermal conductivity of the medium, W/°C«cm

LL = liquid limit as defined by ASTM D423-72 procedures, percent

pF ; = logarithm to the base 10 of the negative pressure (tension, or suction) of the soil moisture in centimeters of water

PL = plastic limit as defined by ASTM D424-71 procedures, percent

;q = power per unit length

r = distance from line heat source

T = temperature rise above initial temperature

t = time elapsed since initiation of heating

TPI = thermal performance index

TSI = thermal stability index

w = inner core moisture content, percent

wj) = minimum moisture content expected under design conditions, percent

^nat ~ natural moisture content, percent

Wqp^ = optimum moisture content using modified energy (ASTM D1557-78

procedures) , percent

W = moisture content, percent

Wg = dry mass of soil, g

Wgc = supercritical moisture content: i.e., the moisture content at which

the thermal resistivity increases with increasing moisture content,

percent

Wt = wet mass of soil, g

o = thermal diffusivity of the medium

X
Euler's constant = 0,5111

dry density, Mg/m-^

thermal resistivity of a sample prepared using modified energy

(ASTM D 1557-78 procedures) and a moisture content equal to the

modified optimum moisture content, °C»cm/W

thermal resistivity of a sample prepared using standard energy

(ASTM D 698-78 procedures) and a moisture content equal to the

liquid limit, °C»cm/W

xi
FACING PAGE: Sample compacted using the 102-mm (4-in) mold

and the 5.5-Ijbf (2.49-kg) hammer according to

ASTM D698-78 procedures.

xii
1. INTRODUCTION

1.1 GENERAL

Evaluation of the thermal properties of soils is a problem facing many

geotechnical engineers. Selection of suitable backfill soils for nuclear

waste disposal sites requires a thorough knowledge of the thermal properties

of the material that surrounds the containment areas and of the factors which

affect these properties. Likewise, knowledge of the thermal properties of

soils is necessary to predict the heat loss in buried structures and in residential housing with slab-on-grade construction. Through an understanding

of thermal soil properties, energy savings are being obtained by using soils

1
to moderate the temperature to which a structure is subjected. The importance

of evaluating thermal properties of soils surrounding buried electric power

cables is evident when one considers that temperatures greater than SO^C to

60°C may lead to breakdown of buried cable insulation if the soil surrounding

the cable is unable to conduct the heat away as it is generated. It is this

need to use soil as an insulating material or as a conductor to dissipate heat

that requires an understanding of the soil characteristics that affect thermal

soil behavior.

In simple terms, soils with a high thermal resistance will not dissipate heat

from a heat source as rapidly as low resistivity soils. The thermal resistivity

of soil is a measure of the thermal performance of soil. It is the reciprocal

of thermal conductivity. The thermal resistivity of the soil is primarily

influenced by: soil composition, moisture content and dry density. When it is

considered that the resistivity (in thermal ohms*) of quartz is 11, water 165

and air 4000, the need for examining each of the three phases (solid material,

water, and air) and their interrelationship is evident. The laboratory testing

program described herein was designed for the purpose of finding low cost,

simple, index property tests and defining soil indices that establish the

thermal behavior of fine-grained soils.

1.2 LIMITATIONS OF PRESENT PROCEDURES USED TO EVALUATE THERMAL SOIL PROPERTIES

Progress in the prediction of thermal soil properties is limited by the fact

that relevant information is scattered in a variety of technical fields. Also,

authors have not used a common language to describe the results of field and

laboratory measurements of these properties.

Geotechnical investigations consisting of in situ and laboratory thermal probe

tests, soil sampling and determinations of moisture and density are frequently

performed to evaluate the thermal resistivity of soils. These investigations

often are conducted using routine procedures adopted over the years, based on research done in the late fifties and early sixties [1],^ but not necessarily

reflecting all the infonnation and techniques now available. Furthermore, much

of the valuable work performed by or under the direction of the Power industry

in the above periods and on which these procedures are based, is reported in

language more familiar to agronomists and electrical engineers [1]. On the

other hand, more recent contributions to the state-of-the-art by geotechnical

engineers are not documented using similar terminology nor correlated with the

findings of the earlier work [2]. This communication barrier limits present

progress in the prediction of thermal soil properties because of possible duplication of efforts with earlier researchers and the inability of researchers and

engineers to exchange information easily and to compile their accumulated

experience using common terminology.

* The thermal ohm is the unit of resistivity. It is defined as the number of

degrees centigrade of temperature drop that occurs when heat flows through a

1 centimeter cube at the rate of 1 watt. The unit of thermal resistivity is

°C«cm/W. Note: 100°C»cm/W = l^K^m/W and .01731°C»cm/W = 1 hr .f t •°F/Btu.

1 Numbers in brackets indicate the literature references at the end of the paper.

2
The key to improving our predictive capability in the field of thermal soil

mechanics is to have a thorough understanding of the soil characteristics that

affect soil thermal behavior and to use this knowledge to develop a common language which will eliminate the communication barrier.

1.3 PURPOSE

The purpose of this study is to provide an approach for determining the thermal

behavior of fine-grained soils using index property tests.

1.4 SCOPE

The index properties of soils (e.g., particle-size distribution and Atterberg

Limits) have been found to correlate well with engineering properties (strength,

stiffness, and compressibility) of soils [3]. By knowing the index properties

of soils, the engineer is able to obtain an indication of the performance of

various types of soils under various engineering situations. At the present

time index property tests are not used in the field of thermal soil mechanics

to provide an indication of the thermal performance of various types of soils.

This is true even though tests, which measure the changes in the state of soil

relative to changes in moisture content, could provide an indication of thermal

soil behavior as a result of the influence of moisture content on the thermal

resistivity of soil. Identification of index property tests to achieve this

purpose was accomplished in this study by:

1. Examining those soil moisture concepts from the fields of agronomy and

geotechnical engineering, that were considered applicable to understanding

better the Atterberg Limits (i.e. the limit states of soil behavior).

2. Measuring the thermal resistivity of a fine-grained soil whose index

properties were known from the AASHTO Materials Reference Laboratory (AMRL)

using laboratory thermal probe tests and establishing the relationships of

thermal resistivity to moisture content at various densities for this

soil. Over 80 thermal resistivity measurements were made on specimens

compacted to various moisture contents and densities.

3. Obtaining index property and thermal resistivity test data for

fine-grained soils from the literature.

4. Correlating the thermal resistivity test data obtained from items 2 and 3 above with the agronomy and geotechnical limit states shown in figure 1-1.*

An example of how this can be done is shown in figure 1-2 from Salomone

[4] which presents Atterberg Limits and thermal resistivity test data

showing the correlation between the Atterberg Limits and soil thermal

resistivity for fine-grained soils.

* Figures are provided at the end of the section in which they are first cited.

3
SOIL MOISTURE

CONDITION DRY MOIST WET SATURATED

Classification

of Soil Moisture

Approximate

Soil Moisture 7,

Tension in pF*

Hygroscopic

Water

Capillary

Water

<

Gravitational

Water

>

Groundwater

).5

<- >

0 4 .5 4.2 22.5 ( .8

STATES OF FINEGRAINED SOIL

BRITTLE SEMISOLID SOLID

PLASTIC

SOLID

LIQUID

Approximate

Agronomy

Limit States

1

(

Friable

iygroscopic

Coefficient

Wilting

Coefficient

Field

Capacity

Settling

/olume

Sticky

Limit

Approximate

Geotechnical

Limit States

(Atterberg

Limits)

Shrinkaj

Limit

;e 1

Plastic

Limit

liquid

.irait

* pF is the logarithm to the base 10 of the negative pressure (tension, or suction) of the soil moisture in centimeters of water.

Figure 1-1. A qualitative comparison of the differences in terminology used by

agronomists and geotechnical engineers (modified from [4]).

4
o

o

600

500

400

> 300

200 -

100 -

Liquid limit = 77%

Plastic limit = 30%

Shrinkage limit = 15%

Brittle solidSemisolid Plastic solid

J. 20 40 60

MOISTURE CONTENT IN PERCENT

80

Figure 1-2. Correlation of thermal resistivity with the Atterberg

Limits (from [4]).

5
FACING PAGE: Using drill press to push laboratory thermal

probe into compacted sample.

6
2. LABORATORY TESTING

2.1 TEST INSTRUMENTATION

2.1.1 General

The equipment used to determine the thermal conductivity (or thermal

resistivity) of the laboratory soil samples tested included:

7
1. Six laboratory thermal probes, and

2. Electric Power Research Institute (EPRI) Thermal Property Analyzer.*

2.1.2 Thermal Probes

Figure 2-1 shows a sectional view of a laboratory thermal probe similar to

those used in this study. Because the interpretation of probe readings depends

on the validity of line heat source theory, exact specifications of the probe

with respect to: uniformity of cross-section along the probe length, thermocouple placement, heater resistance and length, proper insulation against electrical short circuits and mechanical durability must be followed when constructing a thermal probe to comply with the major assumptions of line heat source

theory. The theory is based on the assumptions that the heating element is a straight line of Infinite length and infinitely small diameter. The heating

element is homogeneous and isotropic and is embedded in a homogeneous and

isotropic medium of infinite extent. Also, the heating element possesses the same thermal properties as the surrounding medium.

Wechsler [5] has made recommendations about the construction of thermal probes.

He also presented an abridged version of the line heat source theory upon which

the Interpretation of the probe reading is based. For convenience to the

reader, Wechsler' s [5] presentation of line heat source theory is provided in

the next section. This derivation is based on information found in Ref. [6].

2.1.2.1 Line Heat Source Theory

Consider an infinite line source of heat placed in an infinite homogeneous

medium initially at uniform temperature. Beginning at time t = 0, heat is

released by this source at a rate q per unit source length. The temperature

rise T (above the initial temperature) at a distance r from the line source of

heat is given [6] as a function of time t by:

T = Ei (;4> 4Trk 4at

where k is the thermal conductivity and a the thermal diffusivity of the medium

and Ei indicates the exponential integral evaluated by eq. 2 [6] and tabulated

in the literature [7]:

-Ei (^) =

4at

du.

r^

4at

(2)

* Trade names are identified to specify adequately the experimental procedures.

In no case does such identification imply recommendation or endorsement by

the National Bureau of Standards, nor does it imply that the material identified is necessarily the best available for the purpose.

8
For large values of time, the exponential Integral may be approximated by a series expansion as follows:

-EKZli) . m (^) - (|?-) + \

(I?-)^ + ... -y (3) 4at J.2 4at 4 4at

where y = Euler's constant = 0.5772. By neglecting the terra -1 of first order

and higher In equation 3, and substituting In equation 1, we obtain:

T = _1_ [In -

y] (4)

4'iTk J.2

or

T = [in t + In

^ - y] (5)

4irk J.2 For fixed values of r and a, the temperature rise Increases logarithmically

with time. A plot of temperature rise versus logarithm of time should give a straight line of slope This technique is customarily used with the

line heat source method to evaluate the thermal conductivity. At any point In

the medium, the temperature rise Tj^, at time t]^, is related to the temperature

rise T2 , at time t2, by the following equation:

T2 - Ti = tV In (6)

Thus, in theory, it is possible to obtain a conductivity value if the temperature

rises at only two experimental times are known. To apply eqs. 4, 5, and 6, sufficient times must be allowed so that the exponential integral is approximately

equal to the simple logarithmic expression.

2.1.3 EPRI Thermal Property Analyzer

The EPRI Thermal Property Analyzer was developed by Ontario Hydro Research

Laboratory under an EPRI contract. A manual for the operation and use of the

Thermal Property Analyzer (TPA) was prepared by Ontario Hydro Research

Laboratory [8]. This report describes the TPA as follows.

"The TPA consists of an electric current source and a six-input thermocouple

reader under microprocessor control, housed in a rugged type of attache case. The front-panel layout is shown in figure 2-2. The probe current is determined

on the basis of the resistance/unit length and on the anticipated thermal resistivity to give one of three probe powers per unit length appropriate for soils

of high, medium, and low thermal resistivity. The thermal resistivity is calculated by the microprocessor from a least squares fit to time-temperature data

collected between 300 and 1000 seconds. A special function keyboard is available so that all parameters such as probe powers, times, etc., can be varied

from the pre-set (default) values stored in the microprocessor memory (ROM).

An RS 232 interface which is capable of supporting a printer or other digital

accessories, along with an appropriate printer to produce hard copy of tlme9
temperature data and thermal properties. Is provided. During a "run", the

elapsed time is continuously displayed along with any one of the thermocouple

temperatures, probe power per unit length, or thermal resistivity for any

thermocouple input, based on data accumulated to that time in the run. When

the reset button is depressed, all six thermocouple inputs are scanned and

those without thermocouples attached are ignored in future measurements. If

the temperature of any thermocouple goes over 100°C, the thermal resistivity

for input is "frozen" and future data from that input are ignored. If the

temperture goes over 140°C, the probe power is removed to protect the stability of the heater. The entire system is designed to operate on 90-140 V rms sine wave, or 100-160 V rms square wave; 47-65 Hz.

Numerous error-reducing features are incorporated into the software. For

example, probe power cannot be initiated until the probe has come to thermal

equilibrium with the soil. Also, a coefficient of determination is calculated

for the least squares fit, and an error message is sent if the coefficient of

determination is less than a predetermined value (0.92). Automation of all

aspects of thermal property measurement greatly reduces the likelihood of error in data acquisition and reduction."

2.2 DESCRIPTION OF AMRL REFERENCE SOIL

Participants in the AASHTO Soil Reference Sample Program were provided two boxes

of Soil Reference Samples. Each box was a separate sample of soil marked with a card stamped either #61 or #62. Soil from boxes marked #61 were used for this

study. Each individual test performed by the participating laboratories was conducted by the same operator. However, it was not required that the different

tests be conducted by the same person. Participating laboratories performing

these tests were asked to report the results of a single determination only,

not the average of two or more. All tests were conducted according to the

AASHTO Standards Methods and Instructions [9] . The results are summarized in

table 2-1 [10].

In general, the soil can be described as a silty clay. The Unified Soil

Classification [11] is CL.

2.3 TEST PROCEDURE

2.3.1 General

The laboratory testing program included:

1. Selection of Molding Moisture Content,

2. Soil Preparation,

3. Thermal Probe Sample Preparation,

4. Thermal Probe Tests, and

5. Moisture and Density Determinations.

The procedures used during each of these steps are described below.

10
Table 2-1. Summary of Index Property Test Data

AMRL Soil Reference Sample No. 61 (from [10])

TEST TITLE MO OF

LirvDO .

SAMPLE NO. 61

AVERAGE STAND . DEV

.

C V.

(PERCENT)

PASS NO. 10 PRCNT 1 hf, n o o o 1 r\ 1 1 . 441 5+00 1.465

PACQ MO. 40 1 AO 9 . 6014+01 1 . 189 /+00 1 o o n PASS NO. 200 PRC NT 1 An 8.9855+01 1.8107+00 2.015

PASS .02MM PRCNT 116 0 . U'+UtD+U J. PASS .002MM PRCNT 116 4.5463+01 4.6154+00 10.152

PASS .OOIMM PRCNT 116 3.6035+01 4.4790+00 12.430

LIQUID LIMIT PRCNT 157 4.5121+01 3.6110+00 8.003

PLASTIC LIMIT PRCNT 157 2.3513+01 1.9520+00 8.302

OPT MOISTURE PRCNT 150 1.8396401 1.3899+00 7.555

MAX DENSITY LB/CF 152 1.0800+02 1.7500+00 1.620

SP GR - NO. 10 125 2.7669+00 4.4041-02 1.592

R-VALUE 300 PS

I

17 1.1618+01 6.0396+00 51.986

2.3.2 Selection of Molding Moisture Content

The moisture contents for the thermal probe tests were selected initially based

on those moisture contents required to establish the moisture-density relationship at compactive efforts of standard (5.92 x 105 J/m3) intermediate

(16.16 X 105 j/m3) and modified (26.93 x 105 j/m3) energies. Moisture contents

from 17.5 to 32.5 percent at three percent increments were used for each of

these compactive efforts until the relationship among moisture-density and

compactive efforts were known. With these relationships determined it became

apparent that additional compactive efforts were required to obtain samples

at a wide range of moisture content and density. The compactive efforts used are summarized in table 2-2 in section 2.3.4. Moisture contents required to

determine the relationship of moisture and density for these additional com- pactive efforts were then selected. With the compaction curves known for the

various compactive efforts, the various molding moisture contents (and densities) at which thermal probe tests were to be made were selected by a study of

the compaction curves to obtain thermal resistivity test data for a wide range

of moisture content and density.

2.3.3 Soil Preparation

The soil to be tested was air-dried and a sample was taken to determine the

initial moisture content of the air-dried soil. This was used to establish

the quantity of water required to produce the molding moisture content.

After the desired moisture content (and density) for a test had been selected,

a quantity of air-dried soil equivalent to 2500 g oven-dry weight (or 2000 g

for 5 of the S6 samples tested at the end of the program) was thoroughly mixed

with the necessary amount of water to achieve the molding moisture content.

The soil was then stored in an airtight pan for a minimum curing time of 16

11
hours to absorb the moisture. To provide a controlled environment for the

airtight pan during the curing period, the pan was stored in a plastic bag in

which a minimum of 20 g of water was placed.

2.3.4 Sample Preparation

When the soil test sample had completed curing, a compact ive effort was

selected from those listed in table 2-2, after reviewing the moisture-density

data, to achieve the desired density. The equipment used for sample preparation is described in detail in ASTM D 698-78 [Standard Test Methods for

Moisture-Density Relations of Soils and Soil-Aggregate Mixtures Using 5.5-lbf

(2.49-kg) Rammer and 12-in (305-mm) Drop] and ASTM D 1557-78 [Standard Test

Methods for Moisture-Density Relations of Soils and Soil-Aggregate Mixtures

Using 10-lbf (4.54 kg) Rammer and 18-in (457-mm) Drop] procedures [12].

The following steps were used to prepare the sample:

a. Placed plastic wrap on the baseplate for the 102-mm (4-in) compaction mold

to prevent evaporation of moisture from the bottom of the sample.

b. Attached the mold to the baseplate and recorded the mass on the data sheet

to the nearest 0.1 g.

c. Attached the extension collar to the mold.

d. Placed a sufficient amount of the prepared soil in the mold in layers to

give a total compacted depth of approximately 130 mm (5 in). The number

of layers, weight of hammer, drop height, and blows per layer used

depending on the compactive effort chosen are listed in table 2-2.

e. Removed the extension collar from the mold and removed the exposed

compacted soil with a stiff metal straightedge until the surface was even with the top of the mold. The trimmings (i.e., excess soil when preparing

the test specimen) were recovered and their moisture content determined.

f. Weighed the mold and baseplate plus wet soil to the nearest tenth of a gram.

g. Covered the sample with plastic wrap to prevent evaporation of moisture

from the top of the sample during the thermal probe test.

12
Table 2-2. Summary of Compactive Efforts Used During Laboratory

Testing Program

Description

IJfi "f oh 1" W C X g 1 1 c of Hammer

(Ibf)*

Fall

(ft)*

No. of

Layers

No. of

D i L> Wt> per

Layers

Energy

ft«lbf/ft3*

Modified

(ASTM D1557-78)

10 1.5 5 25 56250

Intermediate 10 1.5 3 25 33750

Standard Plus 5.5 1.0 4 27 17820

Standard

(ASTM D698-78)

5.5 1.0 3 25 12375

S 12 5.5 1.0 3 12 5940

S 6 5.5 1.0 3 6 2970

S 4 5.5 1.0 3 4 1980

* NOTE: 1 Ibf = 4.448 N

1 ft = 0.3048 m

1 ft.lbf/ft3 = 47.88 J/m3

2.3.5 Thermal Probe Tests

Laboratory thermal probe tests were performed using the thermal probes

described in section 2.1.2 and the EPRI Thermal Property Analyzer described in

section 2.1.3. The method of making these tests was changed slightly as experience was gained with this equipment. The procedures that finally evolved

are explained below:

a. Plugged in the TPA and printer and turned power switch on. Allowed a minimum of 10 minutes for warm up.

b. Set the R/L ratio (Probe Resistance) of 610 m^/cm (61Q/m) by the thumbwheel

switches. This is a probe constant which did not change during the

testing program.

c. Set the anticipated thermal resistivity to LOW (thermal resistivity less

than 60°C«cm/watt) . This setting provided the highest coefficient of

determination for the moist samples tested. For the air dried samples

the MEDIUM setting (thermal resistivity between 60 and 120''C 'cm/watt)

provided the best results.

13
d. Set the toggle switch to SINGLE run. SINGLE run Indicates one

16 iiiinute-45 second run at a probe power that is determined by step c. A

setting of LOW provides a power of 0.359 watt/cm (35.9 w/m) while the

MEDIUM setting provides a power of 0.196 watt/cm (19.6 w/m).

e. Inserted the thermal probe into the center of the soil sample using a drill press and in some cases a specially designed cap for the compaction

mold to ensure good soil/probe contact. (The drill press and cap aides

in preventing lateral movement of the probe as it is inserted into the

soil sample.)

f. Connected the probe cables.

g. Depressed the RESET button. This initiated the thermocouple in the probe

being used. (Note that up to six samples can be tested simultaneously.)

h. Waited a minimum of 20 seconds and then pressed RUN button to start

the test. The RUN button initiates probe currents and data acquisition.

i. Observed the probe power, thermal resistivity and coefficient of

determination for the sample(s) being tested during the run (as required)

by using the Data Selector and Thermocouple Selector.

j. Noted the thermal resistivity associated with the highest value of the

coefficient of determination recorded by the printer for each sample

tested following the 1005 second run.

2.3.6 Moisture and Density Determinations

Moisture content and density determinations were performed after the completion

of the thermal probe tests using the following approach:

a. Removed plastic wrap from top of sample and weighed the mold and baseplate

plus wet soil again to determine moisture loss (gain) during the thermal

probe test.

b. Removed a 25-mm (1-in) diameter core of soil from the center of the

sample using a 25-mm (1-in) diameter thin wall tube and determined the

moisture content of the inner soil core using ASTM D 2216-80 [Laboratory

Determination of Water (Moisture) Content of Soil, Rock, and Soil-Aggregate

Mixtures] procedures [12].

c. Separated the baseplate from the mold.

d. Removed a 51-mm (2-in) diameter core of soil from the center of the sample

using a 51-mm (2-in) diameter soil extruder or a 51-mm (2-in) diameter

thin wall tube depending on the consistency of the soil to be extruded.

The thin wall tube was used for soft soil samples. The moisture content

of this outer soil core was determined using ASTM D 2216-80 procedures.

14
e. Extruded the remaining soil from the mold using a 102-ram (4-ln) diameter

soil extruder and determined the moisture content of the sample using

ASTM D 2216-80 procedures.

f. Compared the moisture contents for the inner core, outer core, and total

sample to determine differences in moisture in the thermal probe test

sample.

g. Determined the wet density of the thermal probe test sample using the

wet weight of soil determined in step a. and the volume of the mold

(measured at the beginning of the testing program)

.

h. Determined the dry mass of soil using the equation:

lOOWt

W„ = (7)

s 100+w

where

Wg = dry mass of soil, g

Wt = wet mass of soil, g w = Inner core moisture content, expressed in percent

1. Determined the dry density of the thermal probe test sample using the dry

weight of soil determined in step h. and the measured volume of the mold.

15
100mm

BAKELITE HEAD

DC HEAT SOURCE

HYSOL 15-015 THERMAL EPOXY FILLED

STAINLESS STEEL HYPODERMIC TUBING

3.18mm O.D.

0.33mm THICKNESS

THERMOCOUPLE JUNCTION (TYPE TJ

MANGANIN WIRE HEATER ELEMENT

CONSTANTAN

EPOXY TIP

Figure 2-1. Sectional view of a laboratory thermal probe (from [27])

16
power

a

ON

iA Off

printer probe

m3A m

THERMAL PROPERTY ANALYSER

designed for ELECTRIC POWER RESEARCH INSTITUTE

control

ANTICiMTiO TR PROBE RESISTANCE

smeu UN

RUN RESET RUN

time

Ontario

hydro

research

division

special function access

display

OAT* SELECTOR

THEtlWOCOunWRlECTOR

Figure 2-2. Front-panel layout of EPRI Thermal Property Analyzer (from [8])

17
1

i

FACING PAGE: Connecting the thermal property analyzer to the

laboratory thermal probe,

18
3. THEORETICAL CONSIDERATIONS AFFECTING THERMAL PERFORMANCE OF SOILS

3.1 GENERAL

To provide the readers a better understanding of the findings from this study,

a review of the factors affecting thermal resistivity Is presented. Techniques

used by agronomists and geotechnlcal engineers to predict soli behavior that are applicable to this study are discussed. This background Information which

Is derived from Ref. [4] serves as the basis for the discussion of test results

in section 4.

19
3.2 PRIMARY FACTORS AFFECTING THE THERMAL RESISTIVITY OF SOILS

The thermal resistivity of a soli Is primarily Influenced by the following

parameters

:

a. Soil composition,

b. Density, and

c. Moisture content.

The Importance of these parameters Is discussed below.

3.2.1 Soil Composition

Soil is a three-phase medium composed of solid materials (inorganic and/or

organic), liquid (water) and gases (air). Because heat flowing through soil

must flow through the solid mineral grains and the medium in which they are embedded in a complex system of series and parallel paths, the thermal resistivity of the soil depends on the thermal resistivity of its component materials and the soil structure. This point is important because of the difference

in the thermal resistivity of the various components of the medium. The

thermal resistivity, in thermal ohms ( °C 'cm/watt) , of a mineral such as quartz

is 11, water 165, air 4000 and for organic matter approximately twice as much

as that of the mineral components. Because the resistivities of most minerals

are significantly less than that of water and air, the soil mass should consist

of as much solids as possible if low resistivity is desired. Another consideration is the amount of water that can be adsorbed and/or absorbed by the soil

since we shall see later the importance of soil moisture on soil thermal resistivity. The amount of adsorbed water is affected by the grain size and mineral

content and depends on the geometry of the soil particle surfaces and their

physico-chemical character, as well as on temperature.

3.2.2 Density

Sinclair et al. [13] explained the importance of density when they stated that

"In a dry soil, the solid particles form a system of series-parallel paths with

each other and with the air-filled voids between them. The presence of air

with its high thermal resistivity greatly Increases the overall thermal resistivity of the soil as compared with its soil components because: (1) part of

the heat path is necessarily through the high-resistivity air, in parallel with

the low-therraal-resistlvlty solid material Instead of being all through the

low-thermal-resistlvlty solid material; and (2) because the air makes for poor

contact between the solid particles introducing high-thermal-reslstivlty air

paths in series with the low-thermal-resistlvlty paths through the solid particles." Thus, by reducing the total void volume and improving the contact

between the solid grains through denslfIcatlon of the soil mass a reduction in

the thermal resistivity of the material will be achieved. The density of soils

may be changed by artificial means such as compaction or disturbance of in situ

soils (e.g., during electric cable installation) and by such natural factors as consolidation, shrinkage, or swelling. The least resistivity is achieved in

the case of the greatest amount of solid material per unit volume. At porosities greater than 50 percent to 65 percent, the normal silt-clay soils in a

20
dry state have a thermal behavior determined by the addition of the

resistivities of the component phases while below porosities of 50 percent to

65 percent the thermal behavior is determined from the addition of the thermal

conductivities of the component phases [14]. The transition occurs at lower

porosities for well-graded crushed quartz systems and for sands used as backfill around underground cables (thermal sands). The larger the range of parti

cle sizes, the smaller is the porosity at which this transition occurs. This

transition occurs at a porosity when a contacting granular skeleton is formed

by the grains of the better conducting quartz sands.

Another factor which should be considered when attempting to improve the

thermal stability of a soil is its permeability which determines the potential

moisture movement under thermal gradients. This movement of moisture could be

critical if moisture restoration is curtailed thereby causing the thermal

resistivity to increase. Consequently, an optimum thermal density which is

characterized by a high amount of solid material per unit volume and yet a permeability sufficiently great to allow for moisture restoration should be

used. Also, the type of fine-grained material present is a factor when

attempting to reduce soil thermal resistivity because an expansive clay minera

such as montmorillonite would cause the sand particles to be forced apart

during compaction by swelling action when moisture is added thereby increasing

the thermal resistivity of the soil.

3.2.3 Moisture Content

Recalling the difference in the thermal resistivity between air and water,

another important factor to consider is the extent to which the voids (or pore

spaces) are filled with water. The terms usually used to characterize this

soil property are moisture content and degree of saturation. The moisture

content is defined as the mass of free water expressed as a percentage of dry mass of a given soil volume while the degree of saturation is defined as the

volume of free water expressed as a percentage of the volume of voids.

The importance of soil moisture is illustrated in figures 3-1 and 3-2. As

moisture is added to the soil as a thin film around the soil particles or wedges at the contacts, a path for the flow of heat which bridges the air gaps

between the solid particles is provided. By increasing the effective

contact areas between particles these films or wedges greatly reduce the thermal resistivity of the soil.

When the moisture condition in the soil approaches the wet condition shown in

figure 3-1, the effective contact area no longer increases with increasing

moisture content. Consequently, the significant decrease in thermal resistivity is not evident when additional moisture is added to fill the pore space.

The moisture content at which the bridge mechanism breaks down (with a resulting disproportionate increase in the thermal resistivity with a small

reduction in moisture content) has been referred to as the "critical moisture

content" by Radhakrishna et al. [16]. This critical moisture content depends

on the particle size distribution, particle shape and density. These trends are shown in figure 3-2.

21
Moisture migration is also an important consideration. Thermal gradients

existing in the soil cause a redistribution of moisture in the soil thereby

changing the thermal resistivity of the soil. Because moisture migration under

a thermal gradient involves capillary moisture, i.e., moisture in excess of

adsorbed (hygroscopic) water that is held against the force of gravity [17],

the existing moisture content in the soil is an important consideration in

deciding whether moisture migration is a problem. The rate of moisture migration under thermal gradients is zero outside the limits of the capillary moisture range. In the field of agronomy, the limits of the capillary moisture

range are defined by the hygroscopic coefficient and the field capacity. The

hygroscopic coefficient is the boundary between moist-appearing and dryappearing soil. The field capacity represents the maximum amount of water that can be held against the force of gravity. The maximum migration rate occurs at an intermediate moisture level between the hygroscopic coefficient and the

field capacity, near the wilting coefficient. The wilting coefficient is

defined as the soil-moisture condition at which the ease of release of water to

the plant roots is just barely too small to counter-balance the transpiration

losses. The previously discussed limits are determined by measurements of soil

moisture tension as given by Kohnke [18]. The soil moisture scale which provides the approximate relationship of soil moisture terms that have been referred to is presented in figure 3-3. Figure 1-1 also provides a qualitative com- parison of the differences in terminology used by agronomists and geotechnical

engineers, and it shows that the plastic limit of fine-grained soils is in the

vicinity of the upper limit of the capillary moisture range. Hence, the plastic limit seems to coincide with the negative pressure (tension or suction) of

the soil moisture at which considerable moisture migration occurs upon application of a thermal gradient [19]. Furthermore, Salomone [4] has presented data

that suggest that the plastic limit defined by geotechnical engineers can be

correlated with the critical moisture content. Results from this study, as discussed in section 4 provide additional insight into the relationship among

the critical moisture content, optimum moisture content and the plastic limit

of fine-grained soils.

In summary, we see that the primary factors affecting the thermal resistivity

of soils are: soil composition, density, and moisture content. Empirical

correlations between these factors and thermal resistivity are available (e.g.,

fig. 3-2). However, the key to improving our predictive capability in the

field of thermal soil mechanics is a thorough understanding of the soil characteristics which affect thermal soil behavior. A discussion of these

characteristics follows.

3.3 ASSESSING THE ENGINEERING PROPERTIES OF SOILS

Soil texture, plasticity and cohesiveness form the basis for the soil

classification schemes commonly used by geotechnical engineers. Texturally,

soils are classified as either coarse-grained (sands and gravels) or finegrained (silts and clays) with the dividing line being whether the soil is

retained on/or passes through the 75)jm (no. 200) sieve. The particle size

distribution of sands and gravels have an important influence on their

engineering behavior. For fine-grained soils the engineering properties are greatly affected by the presence of water rather than by the texture alone.

22
The presence of water affects the plasticity and coheslveness of fine-grained

soils by affecting the interaction between the mineral grains. The plasticity

and cohesion of a soil are indicators of soil type. Clays are both plastic and

cohesive while sands are non-plastic and noncohesive (cohesionless) . Silts are intermediate between sands and clays. Silts are fine-grained yet non-plastic

and cohesionless. These relationships have been summarized by Holtz and Kovacs

[3] (table 3-1).

Table 3-1. Textural and Other Characteristics of Soils (from [3])

Soil name: Gravel, Sands Silts Clays

Grain size: Coarse grained

Can see individual

grains by eye

Fine grained

Cannot see

indlA^idual

grains

Fine grained

Cannot see individual

grains

Characteristics: Cohesionless

Nonp la Stic

Granular

Cohesionless

Nonplastic

Granular

Cohesive

Plastic

Effect of water

on engineering

behavior:

Relatively unimportant

(exception: loose saturated granular materials and dynamic

loadings)

Important Very important

Effect of grain

size distribution

on engineering

behavior:

Important Relatively

unimportant

Relatively

unimportant

By mechanical analysis the particle size distribution (texture) of a soil is

obtained. Detailed procedures for this test have been specified by ASTM

D 422-72 (Standard Method for Particle-Size Analysis of Soils) procedures [12].

Atterberg Limit tests [12, 20, 21] are used to measure the plasticity of finegrained soils. The Atterberg Limits are moisture contents which represent

important limit states of engineering behavior (fig. 3-4). By knowing the

natural moisture content of a soil in relation to its Atterberg Limits, the

engineering response of a soil can be predicted. Because Atterberg Limits are limiting moisture contents, these limits of engineering behavior can be shown

on a moisture content continuum (fig. 3-5).

From figure 3-5 we see how geotechnlcal engineers use the results of

classification tests to show: a) types of soil behavior for given ranges of

moisture contents, and b) changes in the state of soil as moisture content

changes. This figure serves to demonstrate the need to establish classification

23
tests which indicate the theraal behavior of soils. Results from this study

discussed In section 4 begin to meet this need for fine-grained soils.

3.4 DETERMINING THE THERMAL BEHAVIOR OF SOILS

3.4.1 " General

Progress In the determination of the thermal behavior of soils has been hampered

by the fact that Information on thermal soli properties that Is scattered In a variety of technical fields has not been consolidated, and professionals

lack a common language to describe the thermal behavior of soils.

Procedures used to evaluate the thermal properties of soils are based on routine

methods adopted over the years but do not necessarily reflect all the Information and techniques now available in the various disciplines faced with the

problem of soil characterization and the prediction of heat transfer in soils.

As part of these routine procedures, heat flow problems are frequently solved

using constant values of soil thermal conductivity from "handbooks" without

considering the factors which affect soil thermal conductivity previously discussed. Also, researchers have not always documented their findings in terminology that is consistent nor correlated their results with the findings of

earlier work [2].

Use of soil as an insulating material or a material to dissipate heat requires

that progress be made in this area and a systematic approach be developed.

3.4.2 Approach

After reviewing the factors that influence the thermal resistivity of soil and

the methods available to assess the type and properties of soils, the hypothesis is advanced that thermal soil behavior can be correlated with the soil

limit states associated with moisture content, which in turn can be identified

by methods developed by geotechnical engineers and agronomists. The program

reported herein was designed to test this hypothesis for one cohesive soil and

examine existing data for other fine-grained soils to determine whether the

findings of the tests also apply to other materials.

The following approach was used:

1. Select one fine-grained soil whose index properties are well known. Hence,

AMRL Reference Soil No. 61 described in section 2.2 was selected.

2. Investigate in detail the Influence of moisture and density on the thermal

resistivity of the AMRL reference soil and correlate the trends with the

limit states of soil behavior (Atterberg Limits) and other index properties

used by geotechnical engineers.

3. Identify the concepts, methods and tests which aid in the determination of

the thermal behavior of the AMRL reference soil using the results from

step 2, above.

24
4. Obtain index property and thermal resistivity test data for other

fine-grained soils. Apply the concepts, methods, and tests Identified for

for the AMRL reference soil to these soils and establish whether they are also appropriate for these soils.

25
Figure 3-1. The effect of soil moisture on the heat flow path

(from [4])

26
600

MOISTURE CONTENT IN PERCENT

Figure 3-2. The effect of moisture content and dry density on the thermal

resistivity of soils (from [15])

27
SOIL SUSPENSION

GRAVITATIONAL WATER

CAPILLARY WATER

HYGROSCOPIC WATER

COMBINED WATER

• Suspension

Settling volume (space occupied

by a unit weight of soil after

settling from a suspension)

Field capacity

Shrinkage limit

Wilting coefficient

Hygroscopic coefficient

Zero vapor pressure (obtained from

oven drying soil at a temperature

not greater than 110°C)

Ignition point (a bright red heat

obtained from heating the soil)

Figure 3-3. Soil moisture scale showing soil moisture terras used by

agronomists (modified from [17])

28
FLUID SOIL-WATER

MIXTURE

LIQUID

o

Soft Liquid limit -p

PLASTIC SCUD Plasticity index

Very stiff Plast

SEMI-SOLID

G)

DRY SOIL

Hard

BRITTLE SOLID

ic limit-^

Shrinkage limit

Figure 3-4. Soil moisture scale showing soil moisture terms (Atterberg

Limits) used by geotechnical engineers for fine-grained

soils (from [4])

29
FACING PAGE: The Laboratory Equipment Used to Determine the Thermal

Properties of Soils,

Shown are the thermal property analyzer with printout

device, and two soil samples with laboratory thermal

probes inserted

,

State:

Water

content:

Brittle solid Semi-solid

LI = Wnat - PL

LL-PL

Plastic solid

limit, SL limit, PL

I Ll<0 Ll=0

STRAIN

0<LI< 1

limit, LL

I Ll=1

W-PL 00

00

oo

STRAIN

Liquid

0 Shrinkage Plastic

1 Liquid

w(%)

LI>1

STRAIN

Figure 3-5. Moisture content continuum showing the various states of

fine-grained soils and the generalized stress-strain response

(modified from [3])

30
4. PRESENTATION AND DISCUSSION OF TEST RESULTS

A.l GENERAL

The tables and figures in this section provide information on: a) the

influence of density and moisture content on the thermal resistivity of the

AMRL reference soil, b) the correlation of the trends observed in part a above

with the compaction characteristics and the Atterberg Limits of the soil used

in the study, and c) the index property and thermal resistivity test data for

other fine-grained soils. A discussion of the data tabulated according to com- pactive effort in tables A-1 through A-8 in appendix A follows. It should be

pointed out that, in most instances, no significant differences in measured

values of thermal resistivity were observed for specimens compacted to the

31
same moisture content and density. However, when comparing thermal resistivity

test data from specimens remolded using S6 and S4 compactive efforts (see section 2.3.4) with thermal resistivity test data from specimens remolded using

S12 compactive effort or greater, additional scatter in measured thermal resistivity were observed for specimens with the same moisture content and dry

density. These differences could be caused by differences in soil fabric of

the specimens tested. Voids were observed on the outer surface of the specimens compacted using the S6 and S4 compactive efforts. Therefore, the data for

compactive efforts of S6 and S4 were not used in constructing figures 4-1

through 4-6.

4.2 EFFECT OF DENSITY

The influence of density on the thermal resistivity of the AMRL reference soil can be seen in figures 4-1 through 4-4. Figure 4-1 shows the variation of

thermal resistivity with changes in moisture content for constant values of

density. By reducing the total void volume and improving the contact between

the solid grains through densification of the soil mass, a reduction in the

thermal resistivity of the material can be achieved. We also see that the

minimum thermal resistivity for a given density occurs as the zero air voids

curve (100 percent saturation) is approached. Examination of the data for the

modified and standard energies in appendix A provides additional insight into

the thermal behavior of this material. The minimum and maximum thermal resistivity under saturated conditions can be approximated by measuring the thermal

resistivity of two samples. One sample should be tested at the optimum moisture content* and maximum dry density* determined using the modified energy and

the other sample should be tested at the liquid limit and that density which

results from using standard energy. A thermal performance index can then be

defined by the slope of the dashed line in figure 4-1. Eq. 8 approximates the

slope of this line as follows:

TPI =

where

P3 ~ Pm (8)

TPI = thermal performance index

pg = thermal resistivity of a sample prepared using standard energy (ASTM

D 698-78 procedures, [12]) and a moisture content equal to the

liquid limit, °C«cm/W

pj^ = thermal resistivity of a sample prepared using modified energy

(ASTM D 1557-78 procedures, [12]) and a moisture content equal to

the modified optimum moisture content, °C«cm/W

LL = liquid limit as defined by ASTM D 423-72 procedures, [12], percent

^opt ~ optimum moisture content using modified energy (ASTM D 1557-78

procedures, [12]), percent.

The terras optimum moisture content and maximum dry density are explained in

section 4.4.

32
For the AMRL reference soil, the thermal performance Index is:

II Z H

= 0*87 " 1. The Thermal Perfo rmance Index, TPI, provides an indication

of the thermal performance of the ARML reference soil under saturated conditions. It measures the change in thermal resistivity per unit change in moisture content over the range of densities expected under natural or artificial

(man-made) field conditions. By taking into account the compaction characteristics and the thermal behavior of the soil, it is expected that this index may

help in comparing quantitatively the thermal behavior of other fine-grained

soils. Figure 4-2 presents the effect of density on the thermal conductivity

of the AMRL reference soil for the purpose of comparison with Kersten data [22].

By keeping the moisture content constant and examining the change in thermal

conductivity with density, the relationships in figure 4-2 and table 4-1 are obtained

.

Table 4-1. Thermal Conductivity-Density Relationships

MOISTURE CONTENT

IN PERCENT

EQUATION OF CURVE FOR

CONDUCTIVITY IN

WATT/ °C. cm*

9.5 k = 0.00007144(10)l-304pd

13.0 k = 0.0O1448(10)0-597p(i

17.0 k = 0. 002803(10)0. 472pd

22.5 k = 0.01802

27.0 k = 0.01657

* For k in W/m.°K multiply by 100

In general, in accordance with Kersten [22], the thermal conductivity varied

with density according to the following equation:

k = AlOB'Pd (9)

where

k = thermal conductivity in watt/'C'cra

= dry density, Mg/m^

A and B = soil constants.

The results in figure 4-2 are in general agreement with the trends observed by

Kersten [22]. However, in contrast to the Kersten [22] data, it was found that

at moisture contents greater than 22.5 percent, the thermal conductivity was

not significantly affected by density. Because the change in the Kersten [22]

trend occurred at a moisture content close to the plastic limit (23.5 percent),

the significance and validity of this finding should be confirmed with thermal

probe tests on other fine-grained soils. This trend is also observed when the

thermal resistivity versus dry density for constant moisture contents is plotted

as shown on figures 4-3 and 4-4. The influence of density on the thermal resistivity continues to decrease until a moisture content in the vicinity of the

plastic limit is reached. At moisture contents close to the plastic limit the

effect of density is minimal.

33
4.3 EFFECT OF MOISTURE CONTENT

The Influence of moisture content on the thermal resistivity of the AMRL

reference soil is shovm in figures 4-1 and 4-5 and table 4-2. Figure 4-1 shows

that for a given density the thermal resistivity decreases with increasing

moisture content until the critical moisture content (knee of the curve) is

reached or, as in the case for the high densities (e.g. 1.84 Mg/m3), until the zero air voids curve is approached. The trend in figure 4-1 suggests that if we want to explore the relationship between thermal resistivity and moisture

content over a wide range of moisture contents for the purpose of correlating

the observed trend with the limit states of soil behavior (Atterberg Limits),

low density samples should be used. Also, a compactive effort which results

in relatively constant density values over a wide range of moisture contents

would be desirable to eliminate the influence of density on the test results.

Figure 4-5 is a plot of the thermal conductivity versus the logarithm of the

moisture content. Such a plot ordinarily gives a straight line for that part

of the data above a certain minimum moisture content. Kersten's [22] data suggests that this minimum moisture content is 7 percent for silt or clay soils.

Considering this fact, straight lines for constant values of density were drawn on figure 4-5. This type of plot appears to fit the data as it did the

Kersten's [22] data, and equations have been developed for the relationships

shown in figure 4-5 (see table 4.2).

Table 4-2. Thermal Conductivity-Moisture Content Relationships

DRY DENSITY

(Mg/m3)

MOISTURE CONTENT

RANGE IN WHICH APPLICABLE

(PERCENT)

EQUATION FOR CONDUCTIVITY

IN Watt/°C • cm*

1.84 12 to 17 k = 0.0215 log w - 0.00506

1.72 9 to 21 k = 0.0186 log w - 0.00576

1.66 14 to 23 k = 0.0169 log w - 0.00487

1.54 14 to 27 k = 0.0146 log w - 0.00441

* For k in W/m»°K multiply by 100

The equations are of the Kersten [22] form:

k = Aj^ log (W) + (10)

where

k = thermal conductivity, W/°C«cm

A;j^ = the slope of the line,

B]^ = the value of the intercept of the curve at 1 percent moisture, and

W = moisture content, expressed as a percent.

34
These equations allow determination of the moisture content of the AMRL soli

If the thermal conductivity is measured and the approximate density is knovm

for the purposes of selecting the appropriate equation. Once again it should

be pointed out that the moisture content referred to in the preceding discussion is the inner moisture content of the center core soil sample as defined

in section 2.3.6. A comparison of the inner, outer, and total moisture content

and the moisture content of the trimmings is provided in tables A-9 through

A-15 in appendix A. There was no significant difference observed among the

inner, outer and total moisture contents. This observation is consistent with

the trend expected for fine-grained, laboratory cured soil samples. Any difference between the moisture content of the trimmings with the other moisture

contents determined results from the rapid rate of drying observed for the

trimmings while the thermal probe test sample was being trimmed. Therefore, a lower initial weight was measured for the trimmings.

The moisture losses (or gains) of the thermal probe test samples during the

thermal probe test are shown on tables A-16 through A-22. The average moisture

loss was -0.04 percent. Seven samples gained moisture during the thermal probe

test. The average moisture gain was 0.01 percent.

4.4 DETERMINATION OF SOIL THERMAL BEHAVIOR

After determining the Influence of density and moisture content on the thermal

resistivity of the AMRL reference soil, an attempt can be made to define an approach which will aid in determining the thermal behavior of fine-grained

soils. Figure 4-6 constructed using the same data as figures 4-2 and 4-5 serves as an aid in estimating the thermal conductivity of the AMRL reference

soil using the moisture content and dry density of the soil. It is also interesting to note that figure 4-6 can be used with the equations in tables 4-1

and 4-2 to estimate the moisture content and dry density of the AMRL reference

soil if the thermal conductivity is known. This concept is important because

as data on other fine-grained soils become available using the form of data

presentation shown, engineers may be able to use the thermal conductivity of

the soil to estimate its moisture content and dry density.

The next step in determining the thermal behavior of the AMRL reference soil is

to correlate its trends in thermal resistivity versus moisture content and dry

density, with its compaction characteristics and Atterberg Limits. When the

dry densities of each sample are determined and plotted versus the moisture

contents for each sample and compactive effort, curves called compaction curves

are obtained (figure 4-7). Each data point on the curves shown represents a single compaction test for which the thermal resistivity was determined. Each

curve is unique for the AMRL reference soil and the method of Impact compaction

and compactive effort used in the program. The peak point corresponding to the

maximum dry density is an important point. It is known as the optimum moisture

content. Note that the maximum dry density is only a maximum for a specific

compactive effort. Increasing the compactive effort increases the maximum dry

density, as expected, but also decreases the optimum moisture content. The com- paction curves flatten out with a decrease in compactive effort. Note too that

the compaction curves, even at higher moisture contents and compactive efforts,

never actually reach the curve for "100 percent saturation" (traditionally

35
called the zero air voids curve) . Test specimens were prepared by 7 different

compaction energies as described in section 2.3.4 to obtain the thermal

resisitivity/conductivity data over a wide range of density and moisture.

The modified energy (ASTM D 1557-78 [Standard Test Methods for Moisture - Density Relations of Soils and Soil - Aggregate Mixtures Using 10-lb (4.54-kg)

Rammer and 18-in (454-mm) Drop] procedures, [12]) and the standard energy

(ASTM D 698-78 [Standard Test Methods for Moisture - Density Relations of Soils

and Soil - Aggregate Mixtures Using 5.5-lb (2.49-kg) Rammer and 12-in (305-mm)

Drop] procedures, [12]) are commonly used by engineers to determine the

moisture-density relation of fine-grained soils. Hence, these energies were selected from the compactive efforts used to mold samples for presentation in

figure 4-7. The S6 energy was selected for presentation because it met the

criteria stated in section 4.3, i.e., it causes a relatively small fluctuation

of density over a range of moisture contents from 10 percent to 30 percent. As we will see later, this characteristic will be helpful in correlating the

thermal resistivity versus moisture content relationship of this soil with its

Atterberg Limits.

The thermal resistivity of test specimens compacted at the dry density and

moisture content shown on the compaction curve are shown on figures 4-8 through

4-14 for each of the compactive efforts used in this study. The minimum thermal resistivity for each compactive effort generally occurs at the point of

optimum moisture content and maximum density. When a plot of minimum thermal

resistivity versus compactive effort is made, the importance of compactive

effort (or density) in achieving the minimum thermal resistivity during placement of this material is seen (figure 4-15).

The correlation of the thermal resistivity versus moisture content relationship

of the AMRL reference soil with its Atterberg Limits is shown on figure 4-16.

When the S6 energy is used to mold the test specimens, the thermal resistivity

increases very rapidly with a slight reduction in moisture content below the

plastic limit of the soil. Thus, the "critical moisture content" at a low density (1.4 to 1.5 Mg/m3) can be found using the plastic limit of the soil under

investigation. For those involved in soil heat transfer problems, this finding

is important. Recalling from figure 1-1 and section 3.2.3 that the plastic

limit generally defines the upper boundary of capillary moisture and that moisture migration under a thermal gradient involves capillary moisture, the negative pressure potential (often termed capillary potential, and more recently

matric potential) of soil water defined by the plastic limit can be used to

determine the thermal performance and stability of a fine-grained soil. If the

measured negative pressure potential of soil water exceeds the negative pressure potential defined by the plastic limit [23], the soil would be expected to

be thermally unstable and moisture migration under thermal gradients would be

likely.

Because geotechnical engineers do not often measure the matric potential of

soil water which results from the capillary and adsorptive forces due to the

soil matrix, figure 4-17 presents an approximate approach for evaluating the

thermal performance and stability of the AMRL reference soil using the moisture

36
content of the soil. Four distinct regions shown on figure 4-17 establish the

thermal performance of this soil. The regions are defined by the moisture

contents shown in table 4-3. Also, the trend in thermal resistivity with

increasing moisture content for each of the regions is described.

Figure 4-17 can also be used to define an index which is a measure of the

thermal stability of the AMRL reference soil at a dry density of 1.4 to

1.5 Mg/m3 and at a particular moisture content. This moisture content should

be the minimum moisture content of the soil that is expected under design conditions. Note that thermal instability occurs in a moist soil as a result of

significant moisture movement when the soil is subjected to thermal gradients

and the moisture content of the soil falls below the critical moisture content.

Therefore a large increase in the thermal resistivity occurs.

The index is called by the authors the thermal stability index and is defined

as follows:

TSI = wsc - PL

(11)

where

TSI = Thermal Stability Index

Wj^ = miniraam moisture content expected under design conditions, percent

PL = Plastic Limit as defined by ASTM D 424-71 procedures [12], percent

wgQ = supercritical moisture content: i.e., the moisture content at

which the thermal resistivity increases with increasing moisture

content, percent.

Table 4-3. Thermal Performance Regions of AMRL Reference Soil (See Fig. 4-17)

REGION OF

THERMAL

PERFORMANCE

DESCRIPTION OF TREND

IN

THERMAL RESISTIVITY

BOUNDARY

MOISTURE

CONSTANT

1 Rapid decrease with increasing

moisture content

PT. A - Oven dry

PT. B - Shrinkage limit

2 Moderate decrease with

increasing moisture content

PT. B - Shrinkage limit

PT. C - Plastic limit

3 No change with increasing

moisture content

PT. C - Plastic limit

PT. D - Supercritical

moisture content

4 Moderate increase with

increasing moisture content

PT. D - Supercritical

moisture content

PT. E - Liquid limit

37
Using the Thermal Stability Index, the thermal stability of this fine-grained

soil can be evaluated according to table 4-4. If the supercritical moisture

constant was not known, the Liquid Limit of the soil could have been

substituted for the supercritical moisture content in equation 11.

Table 4-4. Thermal Stability Index for AMRL Reference Soil

1 THERMAL STABILITY 1 DESCRIPTION OF THERMAL |

1 INDEX (TSI) STABILITY 1

1 TSI _< 0 1 - Unstable

- Moisture migration under theirmal | gradients likely |

1 0 < TSI £ 1 1 - Stable 1 - Moisture migration under thermal | gradients is unlikely

•- Thermal resistivity of the soil is | essentially constant |

1 TSI > 1 1 - Stable 1 - Thermal resistivity increases with | increasing moisture content |

4.5 THERMAL BEHAVIOR OF OTHER FINE-GRAINED SOILS

The literature was examined to obtain data on soils with known index and

thermal properties. This was accomplished after the concepts, methods and

tests described in the preceding sections were identified as being useful when

predicting the thermal behavior of the AMRL reference soil. Because the available information is quite limited and authors measuring the thermal properties of soils often do not classify the soils tested using a common soil

classification system, nor do they provide the index properties and compaction

characteristics of the soil they tested, the information presented was obtained through the cooperation of other researchers. Information in the

literature generally fell into two groups. Group 1 contained those soils in

which stage drying of one sample was performed to determine the thermal resistivity versus moisture content relationship. Group 2 contained those soils in

which the thermal resistivities of samples at different moisture contents and

densities were measured. The thermal resistivity versus moisture content relationship using data from [22] had to be determined by adjusting each thermal

resistivity reported for density. The Kersten equation for fine-grained soils

[22] was used to adjust the measured thermal resistivity for density. The

Kersten equation is:

Thermal conductivity, k = [0.9 log (Moisture Content) - 0.2]100*01 x Unit Wgt.

A summary of the data found in the literature is provided in tables 4-5 and

4-6 and figures 4-18 through 4-24. It should be pointed out that because the

available data were quite limited, only the concepts of correlating the critical moisture content with the optimum moisture content and plastic limit was evaluated.

38
Table 4-5. Correlation of Critical Moisture Content and Optimum

Moisture Content for Other Fine-Grained Soils

CATEGORY

SOIL

DESCRIPTION

UNIFIED

SOIL

CLASSIFICATION

CRITICAL

MOISTURE

CONTENT

(PERCENT)

DRY

DENSITY

OF

SAMPLE

OPTIMUM

MOISTURE

CONTENT

(PERCENT)

FIGURE

AND

REFERENCE

Group 1 Georgia Clay ML 18 77% of

standard

maximum

density

19

(standard

energy)

4-18 Black,

1982, private

coramunication

Niagara Clay CL 20 NA 20

(standard

energy)

4-19, [24]

P4505 Northway

Silt Loam

ML 16 NA 16

(modified

energy

4-20, [22]

P4602 Fairbanks

Silt Loam

ML 16 NA 16

(modified

energy)

4-21, [22]

Group 2 P4710 Fairbanks

Silty Clay Loam

ML 18 NA 18

(modified

energy)

4-22, [22]

P4708 Healy Clay CL 17 NA 17

(modified

energy)

4-23, [22]

P4713 Ramsey

Sandy Loam

CL 9 NA 9

(modified

energy)

4-24, [22]

Little Long Till CL 12 NA 12

(standard

energy)

[24]

The index property and thermal resistivity test data obtained for the other

fine-grained soils shown in Table 4-5 indicate that the critical moisture

content of fine-grained soils can be defined by the optimum moisture content.

To use the optimum moisture content to define the critical moisture content it

is important to understand that:

1) a dry density must be specified when defining the critical moisture content

of a soil because the critical moisture content increases as density decreases

39
(figure 4-1). (The dry density specified can be the in situ dry density

(natural) or a dry density which is a percentage of the laboratory maximum dry

density detertained by some standard test, e.g. standard Proctor test (ASTM

D698-78 procedures) or the modified Proctor test (ASTM D1557-78 procedures').

2) The corapactive effort chosen to determine the optimum moisture content will

depend on the dry density for which the critical moisture content is being

defined

.

3) The critical moisture content is the moisture content at which the minimum

value of thermal resistivity is observed. The index property and thermal

resistivity test data obtained for the other fine-grained soils shown in table

4-6 indicate that the critical moisture content of fine-grained soils can be

defined by the plastic limit for marine sediments that have low natural dry

densities. Hence, it appears that the critical moisture content correlates

with the optimum moisture content for soils over a wide range of densities.

However, as the density of the fine-grained soil decreases to densities typical

of unconsolidated marine deposits, a correlation between the critical moisture

content and the plastic limit is evident.

Table 4-6. Correlation of Critical Moisture Content and Plastic Limit for

Other Fine-Grained Soils

Category Soil Description

Unified

Soil

Classification

Critical

Moisture

Content

(Percent)

Plastic

Limit

(Percent)

Reference

Group 1 Lake Erie

Bottom Sediments

(very soft clay)

CH 30-40 35-45 [25]

Lake Erie

Bottom Sediments

(soft clay)

CH 25-30 25-30 [25]

Atlantic City

Marine Sediments

CH 30 30 [4]

Georgia Strait

Bottom Sediments

OH 66 68

(45-90)

[26]

Malaspina Strait

Bottom Sediments

OH 74 68

(45-90)

[26]

The limited amount of data in the literature, that are available to corroborate

the concepts presented in this report, points to the need for researchers to

consider these concepts when planning the laboratory testing programs for

determining the thermal properties of soils and when reporting their findings.

40
0 15 30 45 60

MOISTURE CONTENT IN PERCENT

Figure 4-1. Variation of thermal resistivity with moisture content

and dry density for AMRL Reference Soil

41
10

8

-

6

- AMRL REFERENCE SOIL SAMPLE NO. 61

4

-

1.0 -

0.8 -

0.6 -

0.4 -

0.2

0.1

9.5%

Numeral indicates number of data points

Moisture Content

Key:

V 9.5%

o 13%

A 17%

22.5%

27%

1.3 1.4 1.5 1.6 1.7

DRY DENSITY IN Mg/m3

1.8 1.9

Figure 4-2. Variation of thermal conductivity with dry density

for various values of moisture content

42
155

t^145

52^135

J2 E

ec " ^ • 125

< o

Z ° 255 115 " 105

TD—

Moisture

content

o3%

1.60 1.70 1.80

DRY DENSITY IN Mg/m3

120

>*- 110

SISTI m/wi 100

90

s°

ec ae

LU — 80

70

r——1 1 rMoisture

o

content

0 10% -

o

1 Q 1 1.60 1.70 1.80

DRY DENSITY IN Mg/m^

90 1

1

1 1 1 \ 1 1

80 - o

m/wa 70

o Moisture

60 content 0

o0 50

o 141/2%

A 12% 0

40 I I 1 1 1 I 1 1 ._ 1.50 1.60 1.70 1.80

DRY DENSITY IN Mg/m^

1.90

I- 2

UJ B

ec "

70

60

50

40

30

1 1 1 1 1 1

1 I

Moisture

content

A 191/2% _ 0 17%

16%

1 1

0

PcP

1 1 1 1 _L 1 1.50 1.60 1.70 1.80 1.90

DRY DENSITY IN Mg/m3

Note: 1 Mg/m3 =

Figure 4-3. Variation of thermal resistivity with dry density for

moisture contents of 3 percent to 18-1/2 percent

43
>-

t—> $3 70

;siSTi m/wa 60

*** o oe 50

ec z UJ — 40

»— 30

content

L 21%

o 23%

I L

1.50 1.60 1.70

DRY DENSITY IN Mg/m3

1.40 1.50 1.60

DRY DENSITY IN Mg/m^

^ 70

UJ o

^o50

S- 40

30

Moisture

Content

o 34%

A37%

V40%

-J I

QO

1.10 1.20 1.30

DRY DENSITY IN Mg/m3

VITY 4-' 70

1—u>

ra 60

CO

UJ E

ec o

_j 50 O

Z o oe

UJ 40

30

Moisture

content

0501/2%

_i I— JL 1.10 1.20 1.30

DRY DENSITY IN Mg/m3

Note: 1 Mg/m3 = 62.4 PCF

Figure 4-4. Variation of thermal resistivity with dry density for

moisture contents of 21 percent to 50-1/2 percent

44
2.4

2.0

1.6

1.2

AMRL REFERENCE SOIL SAMPLE NO. 61

0.8

0.4

Dry Density

in Mg/m3

o 1.84

1.72 ^ 1.66

1.54

2 3 4 5 10 20

MOISTURE CONTENT IN PERCENT

50

Figure 4-5. Variation of thermal conductivity with moisture content

for various values of dry density

45

>-CO

>-ec

1.95

1.90

1.85

1.80

1.75

1.70

1.65

1.60

1.55

1.50

1.45

1.40

1.35

1.30

1.25

1.20

1.15

1.10

1.05

Optimum moisture content

ZERO AIR VOIDS CURVE

(100% saturation] SPECIFIC GRAVITY = 2.76

o Modified energy • Standard energy

A—S6 energy

^Numeral indicates number of data points

1 1 _L 1

- 120

- 115

110

105

100

95 o

Q.

90 S5

85

80

75

70

66

0 10 15 20 25 30 35 40 45 50 55

MOISTURE CONTENT IN PERCENT

Figure 4-7. Compaction curves for modified, standard, and S6 energies

47
>-CO

>-

MODIFIED ENERGY

MOISTURE - DENSITY RELATIONSHIP (COMPACTION CURVE

5^ 1.90 I1.85

1.80

1.75 I1.70

1.65

1.60

1.55

1.50

1.45

1.40

1.35

1.30

Zero air voids curve

^

X

\

Note: 1 Mg/m3 = 62.4 PCF o

A. 15 30 45

MOISTURE CONTENT IN PERCENT

60

MOISTURE - THERMAL RESISTIVITY RELATIONSHIP

»—

'

*—

CO 80 ^

70

o

60

uo 50

>- 40

>

I— 30

LU

OC 20

_l<

10

LU 0

9> o o

o o

Test specimens compacted at the dry

density and moisture content shown

on the compaction curve

15 30 45

MOISTURE CONTENT IN PERCENT

60

Figure 4-8. Correlation of modified energy moisture - density curve with thermal resistivity - moisture content curve

48
INTERMEDIATE ENERGY

MOISTURE - DENSITY RELATIONSHIP (COMPACTION CURVE)

E

>-

LU

>-o

1.85

1.80

1.75

1.70

1.85

1.60

1.55

1.50

1.45

1.40

1.35

1.30

TT-t^

K

\

Zero air voids curve

Note: 1 Mg/m3= 62.4 PCF

X

15 30 45

MOISTURE CONTENT IN PERCENT

60

MOISTURE - THERMAL RESISTIVITY RELATIONSHIP

+-< *-> 110

CO 100

E

o 90

oo 80

>- 70

> 60

1—

</) LU 50

oe

—J<

40

CK

LU 30

1—

20

1 1 1

Test specimens compacted at the dry

density and moisture content shown

on the compaction curve

00

15 30 45

MOISTURE CONTENT IN PERCENT

60

Figure 4-9. Correlation of intermediate energy moisture - density curve with thermal resistivity - moisture content curve

49
STANDARD PLUS ENERGY

MOISTURE - DENSITY RELATIONSHIP (COMPACTION CURVE]

1.85

"

1.80 -

1.75 -

1.70 -

COE 1.65 -

bio 1.60 -

>- 1.55 -

Ui 1.50 - a

>-

oe 1.45 - a

1.40 -

1.35 -

1.30 -

o

o

o o

^

Zero air voids curve

Note: 1 Mg/m3 = 82.4 PCF -

15 30 45

MOISTURE CONTENT IN PERCENT

60

MOISTURE - THERMAL RESISTIVITY RELATIONSHIP

o

oo

CO

80

70

60

50

40

30

20

10

0

o o

o

ooo

Test specimens compacted at the

dry density and moisture content

shown on the compaction curve

15 30 45

MOISTURE CONTENT IN PERCENT

60

gure 4-10. Correlation of standard plus energy moisture - density

curve with thermal resistivity - moisture content curve

50
STANDARD ENERGY

MOISTURE - DENSITY RELATIONSHIP (COMPACTION CURVE)

E

>-CO

o

oo

CO

1.75

1.70

1.65

1.60

1.55

1.50

1.45

1.40

1.35

1.30

1.25

1.20

Zero air voids curve

\

\

Note: 1 Mg/m3 = 62.4 PCF ?

1.13

150

140

130

120

110

100

90

80

70

60

50

15 30 45

MOISTURE CONTENT IN PERCENT

MOISTURE - THERMAL RESISTIVITY RELATIONSHIP

_© 1 1 1

60

Test specimens compacted at the

dry density and moisture content

shown on the compaction curve

OD

15 30 45

MOISTURE CONTENT IN PERCENT

60

Figure 4-11. Correlation of standard energy moisture - density curve with thermal resistivity - moisture content curve

51
S 12 ENERGY

MOISTURE -DENSITY RELATIONSHIP (COMPACTION CURVE)

E

CO

oo

1.70

1.65

1.60

1.55

1.50

1.45

1.40

1.35

1.30

1.25

1.20

Zero air voids curve

o

o\

°\

\

\

Note: 1 Mg/m3= 62.4 PCF

150

140

130

120

110

100

90

80

70

60

50

15 30 45

MOISTURE CONTENT IN PERCENT

MOISTURE - THERMAL RESISTIVITY RELATIONSHIP

-e 1——

60

T T

Test specimens compacted at the

dry density and moisture content

shown on the compaction curve

o o

oo

15 30 45

MOISTURE CONTENT IN PERCENT

60

Figure 4-12. Correlation of S12 energy moisture - density curve with

thermal resistivity - moisture content curve

52
E

>-

S6 ENERGY

MOISTURE - DENSITY RELATIONSHIP (COMPACTION CURVE)

1.65

1.60

1.55

1.50

1.45

1.40

1.35

1.30

1.25

1.20

1.15

1.10

"O

Zero air voids curve

\

OD

O

O

^Numeral indicates number

of data points

Note: 1 Mg/m3 = 62.4 PCF

_L 15 30 45

MOISTURE CONTENT IN PERCENT

60

ra

C3

o

GO

MOISTURE - THERMAL RESISTIVITY RELATIONSHIP ^ 230

210

190

170

150

130

110

90

70 h

50

0

Test specimens compacted at the dry

density and moisture content shown

on the compaction curve

^Numeral indicates number of data points -

O Or

J. 15 30 45

MOISTURE CONTENT IN PERCENT

60

Figure 4-13. Correlation of S6 energy moisture - density curve with thermal

resistivity - moisture content curve

53
>-GO

>-

S4 ENERGY

MOISTURE - DENSITY RELATIONSHIP (COMPACTION CURVE]

1.52

1

1

1

1

1 b 1

50 -

48 -

.46 -

.44

.42

.40

38

36

34

32

30

Zero air voids curve

o

o o

Note: 1 Mg/m3 = 62.4 PCF _

15 30 45

MOISTURE CONTENT IN PERCENT

60

MOISTURE - THERMAL RESISTIVITY RELATIONSHIP

o

CO

80

70

60

50 -

40 -

30 -

20 -

10 -

o

OD

O

Test specimens compacted at

the dry density and moisture

content shown on the compaction

curve

1

15 30 45

MOISTURE CONTENT IN PERCENT

60

4-14. Correlation of S4 energy moisture - density curve with

resistivity - moisture content curve

54
CO

o

oo 60

CO

c;5 40 -

20 - 12 3 4

COMPACTIVE EFFORT - ft-lbf/ft3 x 10*

Figure 4-15. Variation of rainiraura thermal resistivity with compactive effort

55
230

220

210

200 -

190 -

180

170

160

150

140

130

120

110

100

90

80

70

60

50

40

AMRL REFERENCE SOIL

SAMPLE NO. 61

Unified soil classification

Liquid limit = 45

Plastic limit = 23

Shrinkage limit = 16

(estimated)

= CL

o -

Brittle solid

o %

o o

o o o

SL PL

Semisolid

° o

o o

LL

Plastic solid

—I I

Liquid

10 20 30 40

MOISTURE CONTENT IN PERCENT

50

Figure 4-16. Correlation of thermal resistivity and Atterberg Limit

test data using S6 compactlve effort

56
230

220

210

200

190

180

170

S 160

V 150

140 h

oo

^ 130

U> 120 ^ 110

100 k

90

80

70

60

50

40

THERMAL PERFORMANCE OF

AMRL REFERENCE SOIL

SAMPLE NO. 61

Unified soil classification = Liquid limit = 45

Plastic limit = 23

Shrinkage limit = 16

(estimated]

SUPERCRITICAL

MOISTURE = 37

CONTENT

CL

(D

o -

LL

Brittle solid

_i I I

Plastic solid

J I I L

Liquid

10 20 30 40

MOISTURE CONTENT IN PERCENT

50

Figure 4-17. Thermal behavior of AMRL reference soil sample

using S6 compactive effort

57
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63
FACING PAGE: Inserting a ( 1-in) diameter thin

wall tube to obtain the inner core moisture content sample.

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5. CONCLUSIONS AND RECOMMENDATIONS

5.1 CONCLUSIONS

Based on this study, the following conclusions are warranted:

1) The critical moisture content increases as the dry density of the soil

decreases

2) A large increase in thermal resistivity with a small change in moisture

content occurs when the moisture content of the soil is less than the cAtical

moisture content.

65
3) As the corapactive effort for preparing samples was decreased, a corapactive

effort (1.42 x 10^ j/m^) that resulted in the critical moisture content, optimum moisture content and plastic limit being approximately equal was found.

4) The index property and thermal resistivity test data obtained for the AMRL

reference soil and other fine-grained soil indicate that the critical moisture

content can be defined by the optimum moisture content. The compactive effort

chosen to determine the optimum moisture content will depend on the dry density

for which the critical moisture content is being defined.

5) The Thermal Performance Index, TPI, provided an indication of the thermal

performance of the AMRL reference soil under saturated conditions. It measured

the change in thermal resistivity per unit change in moisture content over the

range of densities expected under natural or artificial (man-made) field conditions .

6) The Thermal Stability Index, TSI, defined in this study provided an approximate approach for evaluating the thermal stability of the AMRL soil using

the moisture content of the soil expected under design conditions.

5.2 RECOMMENDATIONS

Based on this study the following recommendations are made:

1) The approach developed for this study was useful when establishing the

thermal behavior of the AMRL reference soils. Because classification and

thermal properties of fine-grained soils are not generally found in the literature, other researchers are encouraged to use the approach described in this

study when measuring and reporting the thermal properties of soils.

2) The concepts used to establish the thermal behavior of the AMRL soil should

be studied further using a wide variety of soils, and exceptions, if any, to the

general trends should be identified.

3) A dry density or the compactive effort used to prepare the samples should

be specified when defining the critical moisture content. The dry density

specified can be the in situ dry density (natural) or a dry density which is a percentage of the laboratory maximum dry density determined by some standard

test, e.g. standard Proctor test (ASTM D698-78 procedures) or the modified

Proctor test (ASTM D1557-78 procedures).

4) Correlations of index properties and the thermal behavior of soils provide

a cost effective method for assessing the probable thermal performance of soils

in an engineering situation. These correlations should be used in conjunction

with those thermal property measurements required to evaluate system performance (viz: underground power cables, heat storage, heat loss into ground and

frost penetration) over the range of operating conditions expected.

FACING PAGE: Extrusion of the remaining compacted sample using soil

extruder for total moisture content determination.

66
6. ACKNOWLEDGMENTS

The writers wish to thank J. Lichtenberg and H. Puluzzi of Potomac Electric

Power Company (PEPCO) and T. Rodenbaugh of the Electric Power Research Institute (EPRI) for making the necessary arrangements which allowed us to use the

EPRI Thermal Property Analyzer during the study. The useful discussions with

T. Rodenbaugh of EPRI, H. S. Radhakrishna , S. Boggs, and J. Steinmanis of

Ontario Hydro and D. Parmer of Geotherm, Inc. about the equipment used in the

study and their experience in thermal property measurements was also greatly

appreciated. The writers wish to thank those providing index and thermal

property data on other types of soil: H. S. Radhakrishna of Ontario Hydro, D.

Parmer of Geotherm, Inc., W. Murphy and D. Horna of Dames and Moore, W. Black

67
of Georgia Tech, T. Nishloka of Arizona Public Service Company, and D. Slack,

J. Mostaghimi and J, Ramsey of the University of Minnesota. In the case of T.

Nishioka of Arizona Public Service Company and D. Slack of the University of

Minnesota, obtaining the required index property data involved performing

additional index property tests. Their special effort is greatly appreciated

by the vnriters.

The writers also acknowledge the assistance of 0. W. Mcintosh of the AASHTO

Materials Reference Laboratory who made the necessary arrangements for obtaining

the required quantities of soil used in the testing program and W. Liggett of

the NBS Statistical Engineering Group for his assistance in analyzing the

thermal resistivity test data. H. S. Radhakrishna of Ontario Hydro reviewed

the report. His comments and suggestions are greatly appreciated. A special

thanks is also given to Brenda Thompson for typing this report.

68
7 . REFERENCES

[1] American Institute of Electrical Engineers "Soil Thermal Characteristics

in Relation to Underground Power Cables," Proceedings from Summer General

Meeting, Atlantic City, New Jersey, 1960, 67 pp.

[2] Fink, L. H., Discussion of "Thermal Instability and its Prediction in

Cable Backfill Soils," Radhakrishna , H. S. and others (1980). IEEE

Transactions on Power Apparatus and Systems . Vol. PAS-99, No. 3, 1980,

p. 865.

[3] Holtz, R. D. and Kovacs, W. D., An Introduction to Geotechnical

Engineering , Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1981,

pp. 26-27.

[4] Salomone, L. A., "Improving Geotechnical Investigations for Underground

Transmission Lines" in Underground Cable Thermal Backfill , Toronto:

Pergamon Press; 1982, pp. 57-71.

[5] Wechsler, A. E., "Development of Thermal Conductivity Probes for Soils and

Insulations," USA Cold Regions Research and Engineering Laboratory,

Technical Report 182 , 1966, 83 pp.

[6] Carslow, H. S. and Jaeger, J. C, Conduction of Heat in Solids , 2nd ed .

,

Oxford University Press, London, 1959.

[7] Jahnke-Emde-Losch, Tables of Higher Functions , McGraw-Hill Book Company,

Inc., New York, 1960.

[8] Ontario Hydro Research Laboratory, "Soil Thermal Resistivity and Thermal

Stability Measuring Instrument, Volume 2: Manual for Operation and Use of

the Thermal Property Analyzer and Statistical Weather Analysis Program to

Determine Thermal Design Parameters," EPRI Final Report No. EL-2128 , 1981,

41 pp.

[9] American Association of State Highway and Transportation Officials.

Standard Specifications for Transportation Materials and Methods of

Sampling and Testing (1978) Part II, Washington, D.C. T87 (pp. 247-249),

T88 (pp. 250-263), T89 (pp. 263-270), T90 (pp. 271-272), T99 (pp. 292-299),

TlOO (pp. 299-302), T180 (pp. 570-577), T190 (pp. 591-601).

[10] AASHTO Materials Reference Laboratory, "Report for Soil Reference Samples

61 and 62," National Bureau of Standards, Washington, D.C, 1981, 23 pp.

[11] U.S. Army Engineer Waterways Experiment Station, "The Unified Soil

Classification System," Technical Memorandum No. 3-357. Appendix A,

Characteristics of Soil Groups Pertaining to Embankments and Foundations,

1953; Appendix B, Characteristics of Soil Groups Pertaining to Roads and

Airfields, 1957, 1960.

[12] American Society for Testing and Materials Annual Book of ASTM Standards , Soil and Rock, Building Stones, Part 19, Philadelphia, 1981, pp. 113-123.

69
[13] Sinclair, W. A., Buller, F. H., and Benham, C. B., "Soil Thermal

Resistivity; Typical Field Values and Calculating Formulas," Fart IV of a report of the American Institute of Electrical Engineers [1], 1960,

pp. 31-43.

[14] Winterkorn, H. F., "Behavior of Moist Soils in a Thermal Energy Field,"

Clays and Clay Minerals , Vol. 9, Pergaraon Press, Oxford, 1962, pp. 85-103.

[15] Salomone, L. A., Singh, H. , and Fischer, J. A., "Geotechnical

Considerations for Designing Underground Transmission Lines," presented

at the 1979 Transmission and Distribution Conference and Exposition,

Atlanta, Georgia, 1979.

[16] Radhakrishna, H. S., Chu, F. Y., and Boggs, S. A., "Thermal Instability

and Its Prediction in Cable Backfill Soils," IEEE Transactions on Power

Apparatus and Systems , Vol. PAS-99, No. 3, 1980, pp. 856-867.

[17] Fink, L. H. , "Soil Moisture Characteristics," Part II of a report of the

American Institute of Electrical Engineers [1], 1960, pp 803-819.

[18] Kohnke, H. , Soil Physics , McGraw-Hill Book Company, New York, New York,

1968, pp. 49^3^":

[19] Gowda, K. R. S. and Winterkorn, H. F., (1949) "Theoretical and

Experimental Exploration of the Practical Possibilities of Electrosmosis

:

Final Report on Beach Stabilization Research (1947-1949)," Part V, Bureau

of Yards and Docks, U.S. Navy, NO. y-15087, 1949, pp. 454-562.

[20] Atterberg, A., "Lerornas Forhallande till Vatten, deras

Plasticitetsgranser och Plasticitetsgrader , " ("The Behavior of Clays

with Water, their Limits of Plasticity and the Degrees of Plasticity,")

Kungliga Lantbruksakaderaiens Handlingar och Tidskrift, Vol. 50, No. 2,

1911, pp. 132-158; also in Internationale Mitteilungen fii'r Bodenkunde,

Vol. 1, pp. 10-43 ("Uber die Physikalische Bodenuntersuchung und ii'ber die Plastizitat der Tone").

[21] Casagrande, A., "Research on the Atterberg Limits of Soils," Public Roads , Vol. 13, No. 8, 1932, pp 121-136.

[22] Kersten, M. S., "Thermal Properties of Soils," Bulletin 28, Engineering

Experiment Station, University of Minnesota, Minneapolis , 1949, 225 pp.

[23] Russell, E. A. and Mickle, J. L. , "Correlation of Suction Curves with the

Plasticity Index of Soils," Journal of Materials, JMLSA, Vol. 6, No. 2,

June 1971, pp. 320-331.

[24] Adams, J. and Baljet, A., "The Thermal Behavior of Cable Backfill

Materials," IEEE Transactions on Power Apparatus and Systems, Vol. PAS-87,

No. 4, 1968, pp. 1149-1161.

70
[25] Radhakrishna, H. S. and Steinmanls, J. E., "Ontario Hydro-General

Public Utility Interconnection Lake Erie Marine Cable Crossing Thermal

Resistivity Surveys," Ontario Hydro Research Division Report 81-378-K,

1981.

[26] Allison, R. W., Cheng, C. L., Griffiths, K. G., and Jue , J. S., "Thermal

Resistivities of Ocean Sediment," in Underground Cable Thermal Backfill , S.A. Boggs et al., Eds., Pergamon Press, Toronto, 1982, pp. 110-118.

[27] Steinmanls, J. E., "Thermal Property Measurements Using a Thermal Probe,"

in Underground Cable Thermal Backfill , S.A. Boggs et al . , Eds., Pergamon

Press, Toronto, 1982, pp. 72-85.

71
I

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A-7
Table A-6. Summary of Laboratory Test Data

S6 Compaction Energy

S6 Energy

1.A2 X 105 J/m3,

2970 ft.lbf/ft3

Identification Moisture Porosity Dry Density Thermal Degree of Volumetric 1 Void

No. Content

% Mg/m3 1 PCF Resistivity

"C •cm/watt

Saturation

% Water Content

TL

1 Ratio

(1) (2) (3) (A) 1 (5) (6) (7) (8) 1 (9)

Air Dry S6 1.95 .419 1.60 1 100.0 228 7.4 3.1 1 .722

11.5 S6 10.00 .458 1 .50 1 93 .4 133 32 .7 15.0 1 .844

14.5 S6 12.33 .477 1 .44 1 90.0 118 37.2 17.8 1 .914

17.5 S6 15.55 .473 1 .45 1 90.7 84 47 .7 22 .6 1 .899

19 S6 (2/3)* 15.13 .474 1.45 1 90.6 87 46.4 22.0 1 .901

19 S6 (2/8) 17.36 .487 1.42 1 88.4 83 50.5 24.6 1 .948

20.5 S6 Stored

16.60 .473 1.45 1 90.7 72 51.0 1 24.1 1 .899

21.0 S6 18.94 .478 11.44 1 89.9 73 1 57.1 1 27.3 1 .916

22.25 S6 20.10 .476 11.45 1 90.3 71 1 61.2 1 29.1 1 .907

23.5 S6 (2/1)

Stored

20.11 1 .469 11.46 1 91.5 67 I 62.9 1 29.5 1 .882

23.5 S6 (2/10) 22.68 .469 11.47 1 91.5 68 I 71.0 1 33.3 1 .882

23.5 S6 (2/12)

Stored

20.68 1 .451 1.51 1 94.6 66 1 69.5 1 31.4 1 .821

24.75 S6 22.60 I .463 [1.48 1 92.5 60 72.4 1 33.5 1 .862

25.0 S6 22.56 .464 1.48 1 92.3 63 1 71.9 1 33.4 1 .866

26.5 S6 (1/27)

Stored

22.76 .459 tl.49 1 93.1

1

66 1 73.9 1 33.9 1 .850

26.5 86 (2/10) 24.53 1 .459 1 .49 I 93.1 63 79.6 1 36.6 1 .850

27(26.5) S6 Stored

24.57 .459 1 .49 1 93.2 59 80.0 36 .7 1 .848

28.0 S6 (2/4) 26.36 1 .465 11.48 i 92.1 59 i 83.6 1 38.9 1 .870

28.0 S6 (2/8) 26.34 1 .465 11.48 1 92.2 59 1 83.8 1 38.9 1 .868

31.0 S6 28.64 1 .468 11.47 1 91.6 66 1 89.8 1 42.0 1 .880

35.0 S6/1 1 34.17 1 .511 11.35 1 84.2 66 1 90.2 1 46.1 11.045

35.0 S6/2 1 33.78 1 .510 11.35 1 84.3 62 1 89.4 1 45.6 11.043

40.0 S6/1 1 36.94 1 .532 11.29 1 80.6 61 1 89.7 1 47.7 11.137

40.0 S6/2 1 36.86 1 .538 11.27 1 79.6 64 1 87.4 1 47.0 11.164

47.5 86 1 41.86 1 .564 11.20 1 75.1 78 ! 89.4 1 50.4 11.293

55.0 86 1 49.48 1 .592 11.12 1 70.3 80 1 94.2 1 55.8 11.450

5.5-lb hammer,

1.0-ft drop,

3 layers, and

6 blows/layer

* Date thermal probe test was performed.

A-8
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A-9
Table A-8. Computed Values for

(100%

the Zero Air Voids Curve for Gg = 2.76

Saturation)

Moisture

Content

%

Dry Density

1 Mg/m3 PCF

(1) 1 (2) 1 (3)

6.8 1 2.32 145

8.4 1 2.24 140

10.0 1 2.16 1 135

11.8 1 2.08 1 130

13.7 1 2.00 1 125

15.8 1 1.92 1 120

18.1 1 1.84 1 115

20.5 1 1.76 1 110

1 23.2 1 1.68 1 105

1 26.2 1 1.60 1 100

29.5 1 1.52 1 95

33.1 1 1.44 1 90

1 37.2 1 1.36 1 85

41.8 1 1.28 1 80

1 47.0 i 1.20 I 75

1 53.0 1 1.12 1 70

1 59.8 1 1.04 1 65

1 67.8 1 0.96 ! 60

1 77.3 1 0.88 I 55

1 88.6 1 0.80 1 50

A-10
Table A-9. Summary of Moisture Content Data

Modified Compaction Energy*

1 Identification | Trimmings | Inner 1 Outer Total

1 No. (Percent) | (Percent) 1 (Percent) (Percent)

1 (1) (2) 1 (3) 1 (4) (5)

1 13.0 M i 10.58 1 10.96

1 17.5 M 1 14.77 I 14.80 I 14.77 14.86

1 20.5 M 1 18.46 1 17.23 1 17.34 17.50

1 23.5 M 1 21.80 1 20.84 1 20.88 20.60

1 25.0 M I 23.05 1 23.10 I 22.91 23.03

1 26.5 M 1 23.81 1 22.95 1 22.99 22.90

1 29.5 M 1 26.17 1 26.92 1 26.59 26.62

1 32.5 M 1 29.57 1 30.01 1 29.85 29.85

1 35.0 M I 34.59 1 34.90 1 34.74 34.57

1 40.0 M 1

1 36.64 1 37.07 1 36.96 36.77

* 10.0-lb hammer

,

1.5-ft drop, 5 layers, and 25 blows /layer.

Table A- 10. Summary of Moisture Content Data

Intermediate Compaction Energy*

1 Identification

|

Trimmings I Inner 1 Outer 1 Total 1

1 No. (Percent) | (Percent) 1 (Percent) I (Percent)

1 (1) (2) 1 (3) 1 (4) 1 (5) 1

1 Air Dried I i 2.29 1 2.89 2.81 1

1 14.5 I 12.60 1 12.21 12.00 1

1 17.5 I 15.61 1 15.79 1 15.52 1 15.93 1

1 19.0 I 16.63 1 16.12 16.34 1

1 20.5 I 19.68 1 18.56 1 18.28 1 18.67 j

1 23.5 I 23.41 1 22.46 1 22.50 1 23.00 1

1 25.0 I 23.51 1 22.81 1 22.82 1 22.86 1

1 26.5 I 24.95 1 25.16 1 25.14 1 25.18 1

1 29.5 I 26.51 1 27.15 1 27.15 1 27.06 1

1 32.5 I 26.90 1 27.38 1 27.04 1 27.26 1

* 10.0-lb hammer

,

1.5-ft drop. 3 layers. and 25 blows /layer.

A-11
Table A-11. Summary of Moisture Content Data

Standard Plus Compaction Energy*

1 Identification

|

Trimmings I Inner 1 Outer I Total 1

1 No. I (Percent) | (Percent) 1 (Percent) | (Percent)

|

1 (1) 1 (2) 1 (3) 1 (^) 1 (5) 1

I 10 s+ i 8.28 1 9.96 10.10 1

1 14.5 S+(l/21)| 12.15 1 12.78 1 12.29 1

1 14.5 S+(1/28)I

1 Stored | 11.98 1 12.22 1 12.62 1

1 17.5 S+ 1 13.69 1 14.71 15.15 1

1 19.0 S+ I 16.44 1 16 .49 1 16.37 1 16.87 1

1 20.5 S+ 1 18.84 1 17.08 17.37 1

1 23.5 S+ 1 17.04 1 18.90 1 18.79 1 19.43 1

1 26.5 S+ 1 23.85 I 22.28 1 22.38 1 22.93 1

* 5.5-lb hammer , 1.0-ft drop. 4 layers, and 27 blows /layer.

Table A--12. Summary of Moisture Content Data

Standard Compaction Energy*

1 Identification

|

Trimmings | Inner I Outer 1 Total 1

1 No. 1 (Percent) | (Percent) 1 (Percent) I (Percent)

I

1 (1) 1 (2) 1 (3) 1 (4) 1 (5) 1

1 Air Dried S | 2.01 1 2.52 1

1 10.0 S 1 8.36 1 8.94 8.80 1

1 17.5 S I 15.05 1 14.38 i 14.63 1 14.97 1

1 20.5 S 1 18.60 1 17.31 I 17.36 1 17.76 I

1 23.5 S 1 20.20 I 20.08 1 19.91 1 20.30 1

1 25.0 S 1 22.02 1 22.78 1 22.49 1 22.68 1

1 26.5 S 1 23.90 1 23.46 1 23.43 1 23.66 1

1 29.5 S 1 25.19 1 26.40 1 26.46 1 26.55 1

1 35.0 S 1 33.83 1 34.49 1 34.29 1 33.87 1

1 40.0 S 1 37.96 1 37.33 i 36.96 1 37.07 1

1 55.0 S I 50.54 I 50.45 1 50.04 1 50.86 1

* 5.5-lb hammer, 1.0-ft drop, 3 layers, and 25 blows /layer.

A-12
Table A13. Summary of Moisture Content Data

S12 Compaction Energy*

Identification

|

Trimmings Inner I Outer Total

No . 1 fPercpnt^ V J- ^0 J- ^> ^— LL t ( Percent ^ fPercent^ ( Percent ^ (1) 1 (2) 1 (3) 1 (4) (5)

Air Dried S12 | 3.71 3.77

10.0 S12 1 8.36 9.70 1 10.02

14.5 S12 1 14.65 14.17 1 14.07

19.0 S12 1 16.89 15.89 1 16.15 1 16.57

20.5 S12 1 19.56 18.19 1 18.45 1 18.54

23.5 S12 I 21.73 21.56 I 21.77 1 21.95

26.5 S12 1 25.45 25.15 1 25.31 1 25.16

28.0 S12 1 25.82 26.29 1 25.95 1 26.06

37.0 S12 1 33.28 33.77 1 33.87 1 33.80

42.0 S12 1 39.51 40.40 1 38.68 1 38.89

* 5.5-lb hammer, 1.0-ft drop, 3 layers, and 12 blows/layer.

A-13
Table A-14. Summary of Moisture Content Data

S6 Compaction Energy*

1 Identification |

1 No. 1 Trimmings

(Percent) | Inner | (Percent) | Outer I (Percent) | Total(Percent)

1 (1) 1 (2) 1 (3) 1 (4) 1 (5)

1 Air dry S6 | 1.97 1 1 1.95

1 11.5 S6 1 9.85 1 10.00 1 9.97 1 10.29

1 14.5 S6 1 13.24 1 12.33 1 12.52 1 12.98

1 17.5 S6 1 14.89 1 15.55 1 15.45 1 15.88

(2/3)**

1 19.0 S6 1 13.37 15.13 1 15.46 1 16.01

(2/8) 1

1 19.0 S6 1 17.68 17.36 1 17.56 1 17.83

1 20.5 S6 1

1 Stored I 15.28 16.60 1 16.68 1 16.95

1 21.0 S6 1 19.31 18.94 1 19.04 1 19.36

1 22.25 86 1 20.16 20.10 1 20.06 1 20.31

123.5 S6 (2/1) I

1 Stored | 19.90 20.11 1 19.85 1 20.37

1 (2/10) 1

1 23.5 S6 1 22.31 22.68 1 22.37 i 22.50

123.5 S6 (2/12) 1

1 Stored I 19.48 20.68 1 20.48 1 20.67

1 24.75 S6 1 22.46 22.60 1 22.46 I 22.74

1 25.0 S6 1 23.07 22.50 1 22.45 1 22.65

126.5 S6 (1/27) I

1 Stored | 24.53

1 22.76 11 23.44 1 23.72

126/5 S6 (2/10) 1 23.59 24.53 1 24.36 1 24.42

127(26.5) S6 1 [stored | 23.98 24.57 1 24.74 1 24.54

1 (2/4) 1

1 28.0 S6 1 26.24 26.36 1 26.54 1 26.33

1 (2/8) I

1 28.0 S6 1 26.02 26.34 1 26.60 1 26.23

1 31.0 S6 1 28.42 1 28.64 1 28.98 1 28.20

1 35.0 S6/1 1 34.72 1 34.17 1 34.75 1 35.19

1 35.0 S6/2 1 33.72 1 33.78 1 33.98 1 33.81

1 40.0 S6/1 1 36.88 1 36.94 1 36.71 1 37.02

1 40.0 S6/2 1 36.96 1 36.86 1 36.92 1 37.02

1 47.5 S6 1 43.04 1 41.86 1 41.82 1 42.54

1 55.0 S6 1 52.58 1 49.48 1 49.63 I 51.26

* 5.5-lb hammer. 1.0-ft drop, 3 layers, and 6 blows /lay er

.

** Date thermal probe test was performed.

A-14
Table A-15. Summary of Moisture Content Data

S4 Compaction Energy*

Identification I Trimmings Inner Outer Total

No. 1 (Percent) (Percent) (Percent) (Percent)

(1) 1 (2) (3) (A) 1 (5)

22.0 S4 1 21.23 20.30 20.52 21.14

26.0 S4 1 24.65 1 24.87 24.79 1 25.08

27.0 S4 1 25.26 25.74 26.39 1 25.78

28.0 S4 1 25.28 25.89 25.92 1 25.80

32.0 S4 I 30.46 1 31.30 31.22 1 31.38

* 5.5-lb hammer, 1.0-ft drop, 3 layers, and 4 blows /layer.

A-15
Table A-16 . Moisture Loss (Gain) of the Test Samples During the

Thermal Probe Test, Modified Compaction Energy*

Identification Mass of mold and base 1 Moisture Percent

No. plate plus wet soil lloss (gain) moisture

(8) 1 (g) loss (gain)

Before 1 After 1 thermal 1 thermal 1 probe test | probe test 1 (1) (2) 1 (3) 1 (4) 1 (5)

13.0 M 6318.8 1 6318.2 1 -0.6 -0.03

17.5 M 1 6396.2 1 6395.2 I -1.0 -0.05

20.5 M 1 6389.4 1 6389.5 1 -0.1 I -0.005

23.5 M 1 6314.1 1 6313.5 1 -0.6 1 -0.03

25.0 M 1 6270.2 1 6269.8 I -0.4 I -0.02

26.5 M I 6265.4 1 6265.1 1 -0.3 1 -0.02

29.5 M 1 6169.4 1 6168.5 1 -0.9 1 -0.05

32.5 M 1 6137.8 I 6137.1 1 -0.7 1 -0.04

35.0 M 1 6044.8 1 6044.3 1 -0.5 1 -0.03

40.0 M 1 6062.7 1 6063.0 1 40.3 1 +0.02

* 10.0-lb hammer, 1.5-ft drop, 5 layers, and 25 blows/layer.

Average loss -0.03 percent

Average gain +0.02 percent

A-16
Table A-17. Moisture Loss (Gain) of the Test Samples During the

Thermal Probe Test, Intermediate Compaction Energy

Identification

No.

Mass of mold and base

plate plus wet soil

(8)

1 Moisture

lloss (gain)

1 (g)

Percent

moisture

loss (gain)

Before | After

thermal | thermal

probe test I probe test

1

1 (1) (2) I (3) 1 (4) (5)

Air Dried I 6088.3 1 6087.6

1

1 -0.7 -0.04

14.5 I 6297.9

17.5 I 6370.8 1 6370.6 1 -0.2 1 -0.01

19.0 I 6355.6 1 6355.8 1 +0.2 1 +0.01

20.5 I 6335.5 1 6335.3 1 -0.2 1 -0.01

23.5 I 6271.0 1 6271.0 1 0.0 1 0.0

25.0 I 6250.3 1 6249.5 1 -0.8 1 -0.04

26.5 I 6209.6 1 6209.6 1 0.0 1 0.0

29.5 I 6191.7 1 6191.3 1 -0.4 1 -0.02

32.5 I 6168.4 1 6166.2 1 -2.2 i -0.12

* 10.0-lb hammer, 1.5-ft drop, 5 layers, and 25 blows/layer.

Average loss -0.03 percent

Average gain +0.01 percent

Table A-18. Moisture Loss of the Test Samples During the Thermal

Probe Test, Standard Plus Compaction Energy

Identification

No.

Mass of

plate

mold and base

plus wet soil

(g)

I Moisture

[loss (gain)

I (g)

Percent

moisture

loss (gain)

Before | After

thermal | thermal

probe test | probe test

(1) (2) 1 (3) 1 (4) (5)

10.0 s+ 6169.1

(1/21)**

14.5 S+ 6155.3 1 6152.8 1 -2.5 -0.14

14.5 S+

Stored (1/28) 6159.6 1 6155.1 1 -4.5 -0.25

17.5 S+ 6255.4 1 6254.8 1 -0.6 -0.03

19.0 S+ 6261.9 1 6261.9 1 0.0 0.0

20.5 S+ 1 6271.4 1 6268.9 1 -2.5 -0.13

23.5 S+ 1 6305.9 1 6305.7 1 -0.2 -0.01

26.5 S+ 6242.7 1 6242.0 I -0.7 1 -0.04

* 5.5-lb hammer, 1.0-ft drop, 4 layers, and 27 blows /layer.

** Date thermal probe test was performed.

Average loss -0.09 percent

A-17
Table A-19. Moisture Loss (Gain) of the Test Samples During the Thermal

Probe Test, Standard Compaction Energy*

Identification Mass of mold and base I Moisture Percent

No. plate plus wet soil lloss (gain) moisture

(g) 1 (g) loss (gain)

Before 1 After 1 thermal 1 thermal 1 probe test | probe test 1 (1) (2) 1 (3) 1 (4) (5)

Air Dried 5991.4 1 5989.8 1 -1.6 -0.10

10 S 6109.6 1 6105.1 1 -4.5 1 -0.25

17.5 S 6146.7 1 6146.7 1 0.0 0.0

20.5 S 6242.2 1 6241.9 1 -0.3 -0.02

23.5 S 6245.8 1 6245.9 1 +0.1 i +0.005

25.0 S 6271.1 1 6270.6 1 -0.5 -0.03

26.5 S 6249.3 1 6247.8 1 -1.5 1 -0.08

29.5 S 6192.5 I 6190.6 1 -1.9 1 -0.10

35.0 S 6081.3 1 6081.0 1 -0.3 -0.02

40.0 S 6040.7 1 6040.8 1 +0.1 1 +0.006

55.0 S 5947.3 1 5946 .6 1 -0.7 -0.04

* 5.5-lb hammer, 1.0-ft drop, 3 layers, and 25 blows/layer.

Average loss -0.07 percent

Average gain +0.005 percent

Table A-20. Moisture Loss of the Test Samples During the Thermal

Probe Test, S12 Compaction Energy*

Identification Mass of mold and base 1 Moisture Percent

No. plate plus wet soil lloss (gain) moisture

(g) 1 (g) loss (gain)

Before 1 After

thermal 1 thermal

probe test | probe test

(1) (2) 1 (3) 1 (4) (5)

Air Dried S12 5980.2 1 5979.7 1 -0.5 -0.03

10.0 S12 6036.0 1 6035.2 1 -0.8 -0.05

14.5 S12 6001.2 1 6000.6 1 -0.6 -0.04

19.0 S12 6020.9 I 6020.6 1 -0.3 -0.02

20.5 S12 6102.3 1 6102.4 I -0.1 -0.006

23.5 S12 6240.0 1 6239.6 1 -0.4 -0.02

26.5 S12 6185.0 1 6184.9 1 -0.1 -0.005

28.0 S12 6179.1 1 6179.1 1 0.0 0.0

37.0 S12 6044.8 1 6044.7 1 -0.1 -0.006

42.0 S12 6009.9 1 6009.3 1 -0.6 -0.01

* 5.5-lb hammer, 1.0-ft drop, 3 layers, and 12 blows/layer.

Average loss -0.02 percent

A-18
Table A-21. Moisture Loss (Gain) of the Test Samples During the Thermal

Probe Test, S6 Compaction Energy*

Identification Mass of mold and base Moisture Percent

No. plate plus wet soil loss (gain) moisture

(g) (g) loss (gain)

Before After

thermal thermal

probe test probe test

(1) (2) (3) (4) (5)

Air

Dried S6 5885.3 5884.9 -0.4 -0.03

11.5 S6 5899.5 5898.4 -1.1 -0.07

14.5 S6 5876.0 5875.4 -0.6 -0.04

17.5 S6 5905.0 5903.9 -1.1 -0.07

(2/3)**

19.0 S6 5897.2 5896.8 -0.4 -0.03

(2/8)

19.0 S6 5888.2 5887.2 -1.0 -0.06

20.5 S6

Stored 5919.0 5918.8 -0.2 -0.01

21.0 S6 5961.0 5961.3 +0.3 +0.02

22.25 S6 5959.1 5959.3 +0.2 +0.01

23.5 S6 (2/1)

Stored 6007.1 6007.1 0.0 0.0

(2/10)

23.5 S6 6045.6 6045.3 -0.3 -0.02

23.5 S6 (2/12)

Stored 6073.3 6073.2 -0.1 -0.006

24.75 S6 6062.8 6062.4 -0.4 -0.02

25.0 S6 6030.6 6030.3 -0.3 -0.02

25.0 S6 (1/27)

Stored 6077.6 6077 .4 -0.2 -0.01

(2/10)

26.5 S6 6072.3 6072.6 +0.3 +0.02

27(26.5) S6

Stored 6099.6 6099.5 -0.1 -0.006

(2/4)

28.0 S6 6079.5 6079.4 -0.1 -0.006

(2/8)

28.0 S6 6110.2 6110.1 -0.1 -0.006

31.0 S6 6132.8 6131.1 -1.7 -0.09

35.0 S6/1 6052.0 6051.7 -0.3 -0.02

35.0 S6/2 6050.4 6049.7 -0.7 -0.04

40.0 S6/1 5988.7 5988.5 -0.2 -0.01

40.0 S6/2 5967.3 5966.8 -0.5 -0.03

47.5 S6 5930.1 5929.3 -0.8 -0.05

55.0 S6 5908.2 5907.4 -0.8 -0.05

* 5.5-lb hammer, 1.0-ft drop, 3 layers, and 6 blows/layer.

** Date thermal probe test was performed

Average loss -0.03 percent

Average gain +0.02 percent

A-19
Table A-22. Moisture Loss of the Test Samples During the Thermal

Probe Test, S4 Compaction Energy

Mass of mold and base ^Ar\ "f G t" n T* o "Po T* r» on t~ No. plate plus wet soil loss moisture

(8) loss

Before After

thermal thermal

probe test probe test

(1) (2) (3) (4) (5)

22.0 S4 5932.5 5932.3 -0.2 -0.01

26.0 S4 6083.6 6083.3 -0.3 -0.02

27.0 S4 6011 .6 6010.6 -1.0 -0.06

28.0 S4 5978.1 5977.8 -0.3 -0.02

32.0 S4 6052.1 6051.8 -0.3 -0.02

* 5.5-lb hammer, 1.0-ft drop, 3 layers, and 4 blows/ layer.

Average loss -0.03 percent

A-20
NBS-n4A (REV. 2-ec) U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. BIBLIOGRAPHIC DATA

KbrUKT NO.

SHEET (See instructions) NBS BSS-149

3. Publication Date

November 1982

4. TITLE AND SUBTITLE

Thermal Behavior of Fine-Grained Soils

5. AUTHOR(S)

Lawrence A. Salomone, William D. Kovacs and Herbert Wechsler

6, PERFORMING ORGANIZATION (If joint or other thon NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Structures Division

Center for Building Technology

National Bureau of Standards, BR, B-162

Washington. D.C. 20234

10. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 82-600636

[^J Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a si gnificant

bibliography or literature survey, mention it here)

Laboratory thermal probe tests performed on an AASHTO standard reference material (a silty clay) showed that thermal resistivity (°C-cm/watt) varies with

soil moisture content and dry density. The tests were performed to correlate

soil thermal behavior with the limit states of fine-grained soils. Over 80

thermal resistivity measurements were made on specimens compacted to various

densities and moisture contents.

Results are presented which indicate that the optimum moisture content of soils

and the Atterberg Limits can be correlated with the thermal behavior of finegrained soils. It was found that the minimum thermal resistivity (i.e., the

critical moisture content) occurred at the optimum moisture content when the

soils were compacted using various compactive efforts. The critical moisture

content defines the knee of the thermal resistivity versus moisture content r curve. When the soils were compacted using a compactive effort of 1,42 x 10

J/m^ (2970 ft-lbs per cubic foot), the minimum thermal resistivity occurred at

the plastic limit of the AASHTO standard reference material. Also, indices are defined which allow comparison of the thermal behavior of fine-grained soils.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Atterberg Limit tests; compaction; compaction tests; heat flow; laboratory tests;

soil moisture; soil tests ; tests ; thermal conductivity; thermal resistivity

13. AVAILABILITY

[X] Unlimited

I I For Official Distribution. Do Not Release to NTIS

[Xn Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

[23] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

102

15. Price

So.oO

USCOMM-DC 6043-P80

-> U.S. GOVERNMENT PRINTING OmCE :1982 O—380-997 (2355)



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