'iDA087 716 ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG--ETC F/S 13/2PAVEMENT EVALUATION AND OVERLAY DESIGN USING VIBRATORY NONDCSTR-ETC(U)
MAY 80 R A WEISS- J W HALL DOT-FA73WAI-377UNCLASSIFIED FAA-RD-77-186-VOL-2 NL
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Report No. FAA-ID-77-116.I Jy4-vj ts
PAVEMENT EVALUATION AND OVERLAY DESIGN USINGVIBRATORY NONDESTRUCTIVE TESTING AND
LAYERED ELASTIC THEORY
Volume RoValidation of Procedure
Richard A. Weiss and Jim W. Hall, Jr.
U. S. Army Engineer Waterways Experiment StationGeotechnical Laboratory
P. 0. Box 631, Vicksburg, Miss. 39180
Of 0T*V4 4 ,"€'' DTIC
MAY 1980 C-FINAL REPORT C
Document is available to the public through theNational Technical Information Service,
Springfield, Va. 22151
Prepared lot
U. S. DEPARTMENT OF TRANSPORTATIONFEDERAL AVIATION ADMINISTRATION
Systems Research & Development ServiceWashington, D. C. 20591
80 87- [
NOTICES
This document is disseminated under the sponsorship of the Departmentof Transportation in the interest of information exchange. The UnitedStates Government assumes no liability for its contents or use thereof.
The United States Government does not endorse products or manufacturers.Trade or manufacturers' names appear herein solely because they areconsidered essential to the object of this report.
~V.
/1 ~ 6_ q7Y 6-v6L Teobmnica Reoret DOcum~utatioe Pa0.s* Report N.. 2. Govsrouseat Accession No. 3. RiieeCt) 9 N
FMA-H77-186-il i/~~.'4. TitIe ndSubiitle $. Rept ew t
VALUATION AND VERLAY IGN SING BRATORY May 19806 ,6. Po.fo._ig r ai, on CoderNDESTIVE..T.STING J..AST]IC THEORY*
olume I1, V IDATION OF EDURE . Performing Organization Repiort No.
' Richard A./ eisag-Jim W.[Hell1, JrP.'5 ' 7je .-, .' a'_. " " e
W-'-'-- ""10. Work Unit No. (TRAIS)
U. S. Army Engineer Waterways Experiment StationGeotechnical Laboratory / &.F7WI 7P. 0. Box 631, Vicksburg, Miss. 39180 V l 'WAM
an__ I Covered
12. Spensering Agency Neme and AddressU. S. Department of Transportation Finl ep2 t
Federal Aviation Administration 0c W T9oe7N ,Systems Research and Development Service ........... - -....Washington, D. C. 2059115. Supplemetesry Notes
16. Alrect
A method of pavement evaluation and overlay design based on vibratory nonde-structive testing and layered elastic theory was developed in Volume I of this report.Volume II validates this method by comparing it with the conventional methods ofevaluation and overlay design for rigid and flexible pavements. Three airportsites were used for the validation. Results of the validation showed good agree-
ment between allowable loads determined from the MDT-elastic theory method and the
conventional standard method. However, there was poor agreement between overlay
thickness requirements determined from the two methods.
I7. Key Werde It. Distributie Stetemet
Nondestructive testing Document is available to the public through
Layered elastic theory the National Technical Information Service,
Pavement design and evaluation Springfield, Va. 22151Validation
19. Security Clessil. (of viis repe,) . Securiy Clessif. (of this pege) 2 meo. of Pges 2. Pl.ce
Unclassified Unclassified 1 6
Fe.. DOT F 1700.7 (-72) Reproduction of completed pae. . ~d 1
PREFACE
This study was conducted during the period October 1977 to
December 1978 by personnel of the Geotechnical Laboratory (GL), U. S.
Army Engineer Waterways Experiment Station (WES), for the U. S. Depart-
ment of Transportation, Federal Aviation Administration, as a part of
Inter-Agency Agreement No. DOT FA73WAI-377, "New Pavement Design
Methodology."
The study was conducted under the general supervision of
Messrs. J. P. Sale and R. G. Ahlvin, Chief and Assistant Chief, respec-
tively, of GL; R. L. Hutchinson and H. H. Ulery, Jr., Chief and Princi-
pal Technical Advisor, respectively, of the Pavement Systems Divisioni;
and under the direct supervision of Messrs. A. H. Joseph, Chief of the
Engineering Investigation Testing and Validation Group; and J. W.
Hall, Jr., Chief of the Prototype Testing and Evaluation Unit. The
programing for this study was accomplished in part by Mr. Ricky Austin,
Research and Analysis Group. Significant contributions were made by
Mr. A. J. Bush III of the Prototype Testing and Evaluation Unit,
and by Dr. W. R. Barker of the Research and Analysis Group. The report
was written by Dr. R. A. Weiss and Mr. J. W. Hall, Jr.
COL John L. Cannon, CE, and COL Nelson P. Conover, CE, were
Directors of the WES during the conduct of this study and the prepara-
tion of this report. The Technical Director was Mr. F. R. Brown.
Aoc ssIa For
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TABLE OF CONTENTS
Page
INTRODUCTION . . . ... 1
BACKGROUND o....................... 1OBJECTIVES .o...................... 3SCOPE ....... ....... ........................... 3
DETERMINATION OF SUBGRADE YOUNG'S MODULUS BY VIBRATORYNONDESTRUCTIVE TESTING ....... ........................ 5
MEASUREMENT OF DYNAMIC STIFFNESS MODULUS (DSM) ..... 5DYNAMIC PAVEMENT RESPONSE COMPUTER PROGRAM SUBE ..... 7LABORATORY RESILIENT MODULUS TESTS ...... ............ 8
ALLOWABLE LOAD-CARRYING CAPACITY AND REQUIRED OVERLAY THICKNESSOF PAVEMENTS ........... .......................... ... 10
COMPUTER PROGRAM PAVEVAL ........ ................. 10LIMITING STRESS AND STRAIN CONDITIONS ...... ......... SSINGLE- AND MULTIPLE-WHEEL LOADINGS ..... ............ 11
VALIDATION .......... ........................... l.....14
LABORATORY AND FIELD SOIL TESTS ... ............. .. 14NUMERICAL VALUES OF THE PREDICTED SUBGRADE YOUNG'S
MODULUS ................................... 14NUMERICAL VALUES OF THE ALLOWABLE LOAD-CARRYING CAPACITY
AND REQUIRED OVERLAY THICKNESS ...... ............. -
SUMMARY AND CONCLUSIONS ........ . ...................... 4,
SUM.,A .RY . . . . . . . . . . . . . . . . . . . .CONCLUSIONS .................... .
REFERENCES ............. .. ........................ 0
S
* %.
INTRODUCTION
BACKGROUND
The increasing expense of pavement construction and rehabilitation
makes it essential to have a fast and reliable method of accurately pre-
dicting the allowable load-carrying capacity and the required overlay
thickness for pavement upgrading. The method of vibratory nondestructive
testing of pavements can play an important part for the rapid evaluation1-6of airport pavements. The U. S. Army Engineer Waterways Experiment
Station (WES) was requested by the Federal Aviation Administration (FAA)
to develop a method of pavement evaluation and overlay design based on
vibratory nondestructive testing combined with a layered elastic theoret-7
ical formalism. This report evaluates this method of pavement evalua-
tion and overlay design.
The method of pavement evaluation and overlay design validation
presented herein consists of determining the subgrade Young's modulus
from the dynamic response of a pavement measured by vibratory nondestruc-
tive tests and using the layered elastic theory and the determined value
of the subgrade Young's modulus to calculate the allowable load-carrying
capacity and the required overlay thickness of a pavement.
Two computer programs, SUBE and PAVEVAL, are used to evaluate a
pavement based on vibratory nondestructive testing and layered elastic
theory. The computer program SUBE calculates the value of the subgrade
Young's modulus from vibratory nondestructive field test data, and the
computer program PAVEVAL calculates the allowable load-carrying capacity
vuid th, required overlay thickness for pavement upgrading.
This study compares the pavement evaluation and overlay design
method that uses vibratory nondestructive testing and layered elasticity
theory with the conventional method for evaluating asphaltic concrete
(AC) pavements that uses the California Bearing Ratio (CBR) and with
the Westergaard method of evaluating portland cement concrete (PCC)
pavements. 8
IJ
The CBR and Westergaard methods required destructive tests to
measure the CBR and coefficient of subgrade reaction, respectively. To
circumvent the destructive tests, a vibratory nondestructive test method
of evaluating AC and PCC pavements was developed at the WES, which
directly correlates the allowable load-carrying capacity and required
overlay thickness to a dynamic stiffness modulus (DSM) that is measured
at the pavement surface. The combined layered elastic theory and vibra-
tory nondestructive test methods of pavement evaluation are also compared
with the direct DSM correlation method.
The DSM is obtained from vibratory nondestructive test data that
are obtained using the WES electrohydraulic vibrator, which can generate
dynamic loads up to 15 kips (peak value) with a constant 16-kip static
load (WES 16-kip vibrator) and a constant frequency of 15 Hz. These
data consist of dynamic load-deflection curves that are measured at the
pavement surface. The dynamic load-deflection curves are nonlinear in
general, and the DSM is the slope of the dynamic load-deflection curve
for a dynamic load of about 10-14 kips. The measured DSM is corrected
to a common pavement temperature of 700F, and the corrected value of the
DSM is correlated to the allowable load-carrying capacity and the re-
quired overlay thickness of a pavement. '6 The DSM method is empirical
and does not take into consideration: (a) the layered elastic structure
of the pavement, (b) the interface conditions between the pavement
layers, and (c) the load transfer across rigid pavement slabs.
In order to improve on the method of directly correlating pave-
ment performance with vibratory nondestructive test data, an attempt was
made to combine the layered elastic theory of pavements with the pave-
ment impedance values measured by vibratory nondestructive testing. In
this way, the pavement structure could be considered. The layered
elastic model of pavements required the Young's modulus and Poisson's
ratio of the subgrade and pavement layers to be known. The elastic
moduli of the pavement layers are estimated by various means, and only
the subgrade Young's modulus is obtained from vibratory nondestructive
test data.
Three airport pavement sites were selected for this validation,
Albuquerque Sunport, Minneapolis-St. Paul International Airport, and
Knox County Airport (Rockland, Maine). Vibratory nondestructive tests
and conventional destructive tests were conducted at these pavement
sites. Pavement properties, such as thicknesses, moisture content,
density, and CBR, were determined by drilling holes through the pavement
layers and the subgrade. Undisturbed subgrade soil specimens were taken
for laboratory resilient modulus tests. Samples of the AC, PCC, base,
and subbase were also obtained for laboratory analysis.
OBJECTIVES
The results of the combined methods of layered elastic and vibra-
tory nondestructive testing are compared with the conventional methods
of pavement evaluation and overlay design. The specific objectives of
this study are:
a. To compare the values of the subgrade Young's modulus pre-dicted from vibratory nondestructive tests by SUBE with thesubgrade Young's modulus values obtained from measured CBRvalues using the relation E = 1500 CBR, and with Young'smodulus values obtained from laboratory resilient modulustests. 0
b. To compare the values of the allowable load-carrying capacityand the required overlay thickness calculated by the layeredelastic theory and the vibratory nondestructive testingapproach with the conventional destructive CBR and Wester-gaard methods and also with the direct correlation DSMmethod.
SCOPE
To achieve these objectives the following experimental work and
analyses were conducted:
EXPERIMENTAL WORK
a. Vibratory nondestructive tests were conducted to obtaindynamic load-deflection curves for AC and PCC pavements atthree airport pavement sites.
b. CBR values were measured for the base, subbase, and subgradeof the pavements at the three airport sites.
3
c. Laboratory resilient modulus tests were conducted onundisturbed soil samples taken from the subgrade at severallocations at the three selected airport sites.
d. Laboratory soil tests were conducted on samples of base, sub-base, and subgrade materials to determine their classification.
ANALYSES
a. The computer program SUBE was used to calculate the values ofthe subgrade Young's modulus from the measured dynamic load-deflection curves.
b. The computer program PAVEVAL was used to determine the allow-able load-carrying capacity and the required overlay thicknessof the pavements at the three airport test sites.
c. The allowable load-carrying capacity and the required overlay
thickness of the pavements at the three selected airport siteswere calculated by the conventional destructive test methodsand by the DSM method, and the results were compared with thelayered elastic method.
....
DETERMINATION OF SUBGRADE YOUNG'S MODULUS
BY VIBRATORY NONDESTRUCTIVE TESTING
MEASUREMENT OF DYNAMICSTIFFNESS MODULUS (DSM)
The WES 16-kip vibrator applies a static load of 16 kips to the
pavement surface and a dynamic load up to 15 kips at frequencies ranging
from 5 to 100 Hz. Both static and dynamic loads are applied to the
pavement surface through a circular 18-in.-diam baseplate. Two types of
vibratory nondestructive tests were performed on pavements:
a. Dynamic load-deflection curves that show the dynamic deflec-tion of the pavement surface as a function of the appliedload.
b. Frequency response spectrum curves that show the dynamicdeflection as a function of frequency for a fixed dynamicload.
Only method a above is used in this study to determine the subgrade
Young's modulus. In general, these dynamic load-deflection curves are
nonlinear, and a nonlinear dynamic theory is required to extract the
value of the subgrade Young's modulus from these measured curves. The
nonlinear dynamic theory is used to remove the extraneous effects of
the static and dynamic loads developed by the vibrator on the predicted
values of the subgrade Young's modulus.3'3 The computer program SUBE
was developed from the nonlinear theory of pavement response to dynamic
loads and is used to determine the subgrade Young's modulus from the
measured dynamic load-deflection curves.
A typical dynamic load-deflection curve measured at 15 Hz is
presented in Figure 1. The dynamic deflection of the pavement surface
is a nonlinear function of the dynamic load applied to the pavement sur-
face. The slope of the dynamic load-deflection curve (tangent modulus)
is called the DSM. The numerical value of the DSM is obtained from the
region of high dynamic loading.
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DYNAMIC PAVEMENT RESPONSECOMPUTER PROGRAM SUBE
The computer program SUBE calculates the value of the subgrade
Young's modulus from input data taken from the measured dynamic load-
deflection curves. The pavement input parameters for the computer
program SUBE include the Young's modulus, the Poisson's ratio, and the
thickness of each pavement layer, as well as the Poisson's ratio of the
subgrade. The computer input that is taken from vibratory nondestructive
test data is the DSM value and a point-by-point description of the
measured dynamic load-deflection curve. The computer program SUBE
iterates the value of the subgrade Young's modulus and determines the
value of the subgrade Young's modulus that makes the theoretically pre-
dicted DSM value agree with the measured DSM value so that the theoreti-
cally predicted dynamic load-deflection curve will agree with the
measured dynamic load-deflection curve. Figure 2 outlines the procedure.
The Poisson's ratio of the wearing surface and base and subbase
courses was chosen according to the rules v = 0.2 for PCC, v = 0.3
for AC pavements and AC base materials, and v = 0.35 for all other
base and subbase materials. The Poisson's ratio for all subgrade soils
is taken to be v = 0.35 . A reasonable estimate of the values of the
Young's modulus of base and subbase materials can be obtained from the2
composition of these materials. When the CBR values of the base and
subbase materials are known, the Young's modulus values can be estimated
from the equation E = 1500 CBR.9
The Young's modulus of the PCC wearing surface of a rigid pave-
ment is taken to be 4.0 x 106 psi. The temperature-dependent Young's
modulus for AC pavement and AC base materials is obtained from Figure 3,
corresponding to the pavement surface temperature at the time of the
vibratory nondestructive testing. The temperature-dependent Young's
modulus value is entered into the computer program SUBE to determine the
subgrade Young's modulus.
r7
DYNAMIC LOAD-DEFLECTION METHOD
BALTIMORE (B2)T = 77" F
AC EI-2."0x1OS P1 0.30 1 5
, BLACK E2 2.0 105 :v20.35 H2 7BASE
G-GM El 3.0 , 104 V3 0.35"3 9
SSM-SC Es ? Ps 0.35a
0 2 4 6 8 10 14DYNAMIC LOAD, KIPS
INPUT DATA1. DSM VALUE2. POINT BY POINT TABULATION
OF LOAD- DEFLECTION CURVE
OUTPT DAA 10 Es 22.6 103~ PSIk M C Es E 281J5
Figure 2. Outline of procedure for predicting thesubgrade Young's modulus from the measured dynamicresponse of a pavement
LABORATORY RESILIENT MODULUS TESTS
It was planned to compare the values of the suh-
grade Young's modulus predicted from vibratory nondestructive field tests
using the computer program SUBE with the values of the subgrade Young's
modulus extracted from the laboratory resilient modulus test. The
labor:itory resilient modulus is expressed in terms of the applied dynam-10-12
ic deviator stress and the static confining pressure.
S
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00
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0 WSU TEST TRACK
z
0.5
0. 140 so so 70 so 90 100
TEMPERATURE -F
Figure 3. Assumed temperature dependence of Young's modulusof AC pavement and AC base materials
ALLOWABLE LOAD-CARRYING CAPACITY AND REQUIRED
OVERLAY THICKNESS OF PAVEMENTS
COMPUTER PROGRAM PAVEVAL
Within the context of the layered elastic theory, pavements are
represented by a stack of elastic layers, the subgrade being of infinite
extent. This layered elastic theoretical model of a pavement structure
is used to calculate the elastic stress and strain at any point in the
pavement or subgrade. Each pavement layer is characterized by a Pois-
son's ratio (v), a Young's modulus (E), and a layer thickness (h). The
Shell BISAR computer program is based on the layered elastic theory and
relates the stress and the strain in each pavement layer to the static
load applied to the surface of a pavement. Figure 4 represents a typi-
cal pavement structure according to the layered elastic theory approach.
LOADING
WEARING SURFACE El V1 hi
BASE E2 2 h2
SUBBASE E3 3 h3
/ / / 7 /-SUBGRADE E4 4
Figure 4. Typical pavement structure with loadingaccording to layered elastic theory
Experience has shown that the condition of failure in AC pave-
ments can be described by a limiting elastic (resilient) vertical strain
in the top of the subgrade and a limiting tensile strain at the bottom
of the AC pavement layer, while the condition of failure in rigid pave-
ments can be described by a limiting tensile stress at the bottom of the13,14PCC layer.1 ' For a given load at the pavement surface, the values of
the stress and the strain in the pavement and the subgrade depend on
10
the Young's modulus and the Poisson's ratio of the subgrade and each
pavement layer.
For the evaluation of a pavement and the determination of the
required overlay thickness, the basic BISAR computer program was modi-
fied to include a procedure for iterating the surface load and the over-
lay thickness until the vertical strain at the top of the subgrade for
AC pavements equals the limiting vertical strain value or the tensile
strain at the bottom of the AC layer equals the limiting value of the
tensile strain, and until the tensile stress at the bottom of the PCC
layer of rigid pavements equals the limiting value of tensile stress.
The resulting computer program called PAVEVAL is used to calculate the
allowable load-carrying capacity and the required overlay thickness of
a pavement.1 The aircraft characteristics required for the computer
program PAVEVAL include the tire contact area, the load on one wheel,
wheel spacings, and the total number of main gear wheels.
The computer program PAVEVAL was written to incorporate the
material parameters and the limiting stress and strain criteria into a
procedure for calculating the allowable load-carrying capacity and the
overlay thickness required for pavement upgrading. PAVEVAL, used in
conjunction with the computer program SUBE that predicts the value of
the subgrade Young's modulus, was developed to be a practical tool for
the pavement engineers to use for evaluation and overlay design purposes.
Figure 5 gives a flow diagram for the general procedure used for pave-
ment evaluation and overlay design.
The choice of the elastic moduli of the pavement layers that are
entered into the computer program PAVEVAL is the same as those selected
for the computer program SUBE with the exception that the Young's modu-
lus of AC pavement and AC base materials was chosen to have the value
E = 450,000 psi in PAVEVAL for the numerical calculations made in this
study. This value of the Young's modulus is obtained from Figure 3,
corresponding to an assumed average yearly pavement temperature of 70*F.
This temperature value was chosen in order to compare the results with
the DSM evaluation procedure, which assumes a yearly temperature average
of 700F. However, PAVEVAL has a greater capability for pavement
11
NDT DATA ICOMPUTER PROGRAMDYNAMIC LOAD - SUBE CALCULATESDEFLECTION CURVES THE SUBGRADE
YOUNG'S MODULUS
ES
ELASTIC MODULI OFPAVEMENT LAYERS L E
THEORY COMPUTER PROGRAMPAVEVAL
LIMITING STRESSSoAND STRAINI
ALLOWABLE LOAD- CARRYINGCAPACITY AND REQUIRED
OVERLAY THICKNESS FOR ACAND RIGID PAVEMENTS
Figure 5. Pavement evaluation and overlay design by thecombined methods of layered elastic theory and vibratorynondestructive testing
evaluation purposes because it can be used to study the seasonal varia-
tion of pavement allowable load-carrying capacity by using Figure 3 to
select the proper seasonal variations in the value of the Young's modu-
lus of AC pavement layers. For this purpose, the seasonal variation of
the base, subbase, and subgrade Young's moduli must also be considered,
such as during frost thaw conditions. The seasonal variation of these
Young's moduli values may possibly be determined either by conducting
vibratory nondestructive tests during the different seasons or by extrap-
olating laboratory-measured Young's moduli according to seasonal temp-
erature and moisture changes.
L , .... .. 1"2
LIMITING STRESS AND STRAIN CONDITIONb
The allowable load-carrying capacity of a pavement and the overlay
thickness required for pavement upgrading are related to the limiting
tensile strain at the bottom of the AC layer and to the limiting verti-
cal strain at the top of the subgrade for AC pavements, and to the
limiting tensile stress at the bottom of the PCC layer for rigid pave-
ments.1 3 15 The limiting value of the vertical strain at the top of the
subgrade depends on the number of strain repetitions and on the value of
the Young's modulus of the soil in the subgrade.
The lateral distribution of traffic was handled by using pass-to-
coverage ratios for individual aircraft.16 ,1 7 Mixed traffic was not
considered in this study, but it can be incorporated into PAVEVAL pro-
vided the frequency distribution of operating aircraft is known.
SINGLE- AND MULTIPLE-WHEEL LOADINGS
To determine the allowable load-carrying capacity and the required
overlay thickness for a single-wheel loading on a pavement surface, the
stress and the strain due to the single load are compared with the
limiting stress and strain values in the pavement and the subgrade. The
load on one wheel is entered into the computer program PAVEVAL.
Actual aircraft loadings on a pavement occur through two or more
wheels in close proximity. Dual-wheel (two-wheel) and dual-tandem-wheel
(four-wheel) configurations are commonly used. For the case of multiple
wheels, the total strain or stress in the pavement beneath one wheel is
due in part to the presence of the other wheels. The maximum values of
the stress and the strain at some depth in the pavement occur at a point
between the wheels. However, a good approximation of these maximum
values can be obtained by calculating the values of the stress and the
strain at the same depth in the pavement and directly beneath one of the
wheels. The multiple-wheel calculations in the computer program PAVEVAL
are made within this approximation. PAVEVAL, as well as the BISAR pro-
gram on which it is based, calculates the stress and the strain at any
* point in the pavement due to a multiple-wheel loading and can also com-
pare them to their corresponding limiting values.
13
VALIDATION
LABORATORY AND FIELD SOIL TESTS
Laboratory soil classification tests were performed on the samples
taken from the base, subbase, and subgrade at the three airport pavement
sites investigated. Field measurements of the thickness and the CBR
were also made of the base, subbase, and subgrade materials by drilling
core holes (small aperture tests 8). The coefficient of subgrade reac-
tion that is required for the Westergaard calculation of PCC pavement
strength using the Westergaard theory was obtained indirectly from
measurements of the subgrade CBR.1 8 The Young's moduli of the material
in the pavement layers was calculated from the formula E = 1500 CBR.9
The mean pavement temperature was measured for AC wearing surfaces at
the time the vibratory nondestructive tests were conducted. Tables 1-3
present the results of the field and laboratory tests.
The subgrade soils at the three airport sites were inhomogeneous,
and accurate CBR measurements could not be made. The subgrade soil at
the Knox County Airport, Rockland, Maine, contained rocks and boulders,
and at the Minneapolis-St. Paul International Airport, the subgrade
often was a thin layer of soil overlying bedrock.
Laboratory resilient modulus values were also measured for a series
of dynamic deviator stresses and static confining pressures on undis-
turbed subgrade soil samples taken from the pavement sites. Most of
the subgrade soil samples taken from the Rockland and Minneapolis-St.
Paul sites were too poor in quality to perform resilient modulus tests,
but the subgrade soil samples from the Albuquerque site produced some re-
silient modulus measurements. Figures 6-15 show the results of the
resilient modulus measurements.
NUMERICAL VALUES OF THE PREDICTEDStrBGRADE YOUNG'S MODULUS
At each pavement location, four dynamic load-deflection curves
were measured at 15 Hz. The computer program SUBE was used to determine
a predicted value of the subgrade Young's modulus for each measured
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~1 '~a z -
a- a~ a"
.0 0% '0 - C a, 0 - N a,
17
1000- ALBUQUERQUE SITE g900 ML. SILTY SAND
700
600-
400
300
200
-j100
80
zUJ 70
w60CL S 40 PSI
50 3
10
40 -20
30
20 5
NOTL 1%TATIC CONFIN-NG PRIFSIN[
101I0 10 20 30 40 50 60 70
DYNAMIC DEVIATOR STRESS C-D PSI
Figure 6. Resilient modulus test, Albuquerque-9
1000 -ALBUQUERQUE SITE It900- ML, SILTY SAND600
700
600
400-
300-
200 r
-j100
0 90-
80
w
w 60
30
20
NOTE STA11C CONFININO F't t, ,1I13
100 10 20 30 40 50 60 70
DYNAMIC DEVIATOR STRESS G-D, PSI
Figure 7.Resilient nioduiths test, Albuquerque-li
19
loo0 ALBUQUERQUE SITE 12SC. CLAYEY SAND
90
70
60
"~40
30
0 3
zw-J
in
20 10 20
NOTEi o STATIC CONFINING PRESSURE
l iII I0 10 20 30 40 s0 60 70
DYNAMIC DEVIATOR STRESS a-,PSI
Figure 8. Resilient modulus test, Albuquerque-12
20
1000 ALBUQUERQUE SITE 13900 SC, CLA-,f Y SAND800
700
500-
400
300
200
00
090
oso
wA 70
w60 44 S
40S
3
.30-
1020
-(
NOTE 'SSTATIC CONFINING PRESSURE
0 10 20 30 40 s0 60 T0DYINAMIC DEVIATOR STRESS 0-, S
Figure 9. Resilient modulus test, Albuquerque-1S
21
1000o ALBUQUERQUE SITE 14900 SM. SILTY SANDa00
700
600-
500-
400
300
200
00
90
20
700
N50 ST TI COSNN 30 PSI'R
0302 405 20 7
DYNAMIC DEVIATOR STRESS 0-D, PSI
Figure 10. Resilient modulus test, Albuquerqiie-1 1'
22
100- ALBUQUERQUE SITE 17SC-SM, SILTY SAND
90-
8o
70
60-
40
N
20 PSI
030 -0
zw
U) 10.
N
20-
NOTE oS STATIC CONFINING PR! =;,LIH[;
0 - S0 20 30 40 so 0 70DYNAMIC DEVIATOR STRESS UDI PSI
Figure 11. Resilient modulus test, Albuquerque-17
23
100 ROCKLAND SITE ICL, SANDY CLAY WITH GRAVEL
90
70
'I
60
so "o-II
50
409L
NOTE CS STATIC CONFINING PRESSURE
S300
a \" \\\\
20
03
0 10 20 30 40 50 60 70DYNAMIC OEVIATOR STRESS G-, PSI
Figure 12. Resilient modulus test, Rockland-i
24
1000- ROCKLAND SITE 4goo- CL, SANDY CLAYmDo700
600
So00
400
300
200
80
zWAJ 70
W 60 J
50
40
.30
30 OPSI20 20
NOTE STATIC CONFINING PRESSURE
5 10
100 10 20 30 40 so0s 70
DYNAMIC DEVIATOR STRESS G0 , PS
Figure 13. Resilient modulus test, Rockland-4
25
00 -- ROCKLAND SITE 7
90 -CL, LEAN CLAY WITH SANDso
70
0so
40
30
20
2IkI
4 \01-o 9
S8-
zW 7 -
5 0" 20 PSI
4-
3-
2
NO | " 'TA1 I." cCONFINING. PI?,I SS IIRI
6I I I0 10 20 30 40 P 0 60 70
DYNAMIC DEVIATOR STRESS 0 -"D PSI
Figure 14. Resilient modulus test, Rockland-7
26
Do- MINNEAPOLIS-ST PAUL R/W IlLSM, SILTY SAND
90
so
70
Go
so
N 40 PSI
40 N N30I NN
if o-I N .=. .. m
-J
30 00
zw-j
20o
NOTE STATIC CONFINING PRE;.',SJRE
5
0 to 20 30 40 50 so 70DYNAMIC DEVIATOR STRESS aD, PSI
Figure 15. Resilient modulus test, Minneapolis-St. Paul-ilL
27
dynamic load-deflection curve. The set of predicted Young's moduli at
each location was averaged, and this average value of the subgrade
Young's modulus appears in Tables 1-3 for each test location at the
three airport sites. The four values of the Young's modulus predicted
at each location did not vary by more than 15 percent, so the average
value represents the subgrade Young's modulus for a given location.
A simple relationship between the subgrade Young's modulus and
the CBR has been obtained by wave propagation techniques and is given
by the empirical formula E = 1500 CBR, where E represents the sub-s s
grade Young's modulus. The nonlinear dynamic theory of pavement response
and the associated computer program SUBE were developed to predict
values of the subgrade Young's modulus that are in reasonable agreement
with the predictions of E = 1500 CBR.s
Figure 16 shows a comparison of the subgrade Young's modulus
values predicted by the nonlinear dynamic response theory through the
computer program SUBE and the subgrade Young's modulus values derived
from the empirical formula E = 1500 CBR. Figures 17 and 18 give a5
comparison between the values of the subgrade Young's modulus obtained
from the laboratory resilient modulus tests and from the SUBE and 1500
CBR methods, respectively.
The Young's modulus of a soil can be extracted from the resilient
modulus that is measured in the laboratory. The resilient modulus is
a measure of the response of a soil to dynamic loads. Its value depends
on both the static and dynamic loads. The Young's modulus is a measure
of the response of a soil to static loads, and its value depends only on
the static confining pressure. The resilient modulus and the Young's
modulus cannot be used interchangeably. The extraction of the Young's
modulus from the resilient modulus by the method given in Reference 4
was not done for this validation report. Instead, as a first approxima-
tion, the values of the resilient modulus for zero dynamic load were
used to obtain the Young's modulus values for the comparison with 1500
CBR shown in Figures 17 and 18.
The choice of zero dynamic load is made because the Young's
modulus is a static elastic quantity that is defined for zero dynamic
S/
240A
2206
200 £
180 -
i140-
1120
I I)w
so--0 ALBUOUEROUE (AC)0 ALBUOUEROUE (PCC)
60 - 0 ROCKLAND (AC)" MINNEAPOLIS-ST. PAUL (PCC)
0040
6
0~ , , I I I I I
0 20 40 60 80 100 120 140 I) IS1
SUBGRADE YOUNGS MODULUS (1500 CDR), 103 PSI
Figure 16. Comparison of predicted and measured subgrade Young's moduli
29
700-
600 0 SUBE COMPUTER PROGRAM
500 0 1500 CAR
RESILIENT MODULUS CORRESPONDS
400 TO o 0 AND ". - 5 PSi
yD = DYNAMIC DEVIATOR STRESS
a, = STATIC CONFINING PRESSURE
300- 0 0 ALBQ-9
0 0 ROCK-4
200 - 0 ALBQ-11
U,
0 0 ALOQ-13
J00 00 0 ALBQ-14
z0 90 - ROCK-7
so 0 ROCK-1 o ALBQ-17
z 0 o A4NN-IILWU 70
w 0
50 -
40 -
30-
0 0 ALBQ-12'0 -
0 '0 20 30 40 50 60
SUIGRADE YOUNG'S MODULUS, 10 3 PSI
Figure 17. Comparison of values of the subgrade Young's muodultu a
predicted by SUBE, by 1500 CBR, and by extraction from the l.,bnra-
tory resilient modulus test at a 8 5 psi
30
700
600-0 SUBE COMPUTER PROGRAM
So 0 1500 CBR
RESILIENT MODULUS CORRESPONDS
400 TO ,a 0 AND .s W I1
DYNAMIC DEVIATOR STRLSS
STATIC CONFINING PRESSURe
300
0 0 ROCK-4
2OO 0 0 ALBQ-14
IL4"2
I-J.ao 0O 0 ALBQ-.II
0so-
W O 70 6 0 ROCK-10 0 ROCK-7
w~ 600 0 ALBQ-9
so-
0 0 ALBQ-13
60 - 0 ALBQ-17
40 - 0 ALBQ-12
0 MINN-IIL
20
,oI 1 I I I
0 10 20 30 40 50 60 70SUSGRADE VOCNG'S MODULUS, 0 3 PSI
Figue . Comparison of values of the subgrade Young's modulus aspredicted by SUBE, by 1500 CBR, and by extraction from the labora-tory resilient modulus test at as 1 0 psi
31
loads. Furthermore, the CBR measurement is made under static loading
conditions, and it should likewise be compared with a static elastic
modulus--the Young's modulus extracted from the resilient modulus.
Finally, the formula E = 1500 CBR is determined from wave propagation
tests under vanishingly small dynamic pressures, so that the Young's
modulus determined in this way refers essentially to zero dynamic load-
ing. No doubt better agreement with the resilient modulus is possible
if larger values of dynamic deviator stress are chosen, but the choice
is arbitrary and any amount of agreement could be obtained by an appro-
priate choice of value for the dynamic deviator stress.
NUMERICAL VALUE OF THE ALLOWABLELOAD-CARRYING CAPACITY AND REQUIREDOVERLAY THICKNESS
For a validation of the procedures outlined in this study, a
number of rigid and flexible pavement structures at the three selected
airport sites were evaluated for single- and multiple-wheel loadings,
and the allowable load-carrying capacity and the required overlay thick-
ness were the results of nondestructive testing and layered elastic
theory. For these pavement structures, the allowable load-carrying
capacity and the required overlay thickness were also determined by the
conventional CBR and DSM methods for AC pavements and by the Westergaard
and DSM methods for rigid pavements. Tables 4-12 and Figures 19-22 show
the results.
In Tables 4-12, the allowable load is expressed in terms of total
gross aircraft load and the load on one wheel of each aircraft. Figure
19 presents comparisons of the allowable load on a single wheel with
contact area of 254 sq in. This contact area corresponds to the contact
area of the 18-in.-diam load plate of the 16-kip vibrator. Figure 20
makes similar comparisons for the allowable gross load of a DC-8 aircraft.
Figures 23 and 24 show the effect of varying the elastic proper-
ties of the pavement layers on the resulting allowable load in the
layered elastic theory. These figures give the preliminary results of a
sensitivity study for AC pavements, which shows the dependence of the
predicted allowable load-carrying capacity on the values of the Young's
32
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120
100-@
so 0o 00
_9 4 ROALAND (AC)
"o0 60 6 ,; ,'
0.-
j 40 2 0 s ALBUQERQU (AC
8 0 II0 ROCKLAD AC)
I I _ I I L I I
O0 20 ,40 60 80 100 120 140
ALLOWABLE LOAD, KIPSDS?, METHOD
120
LA
100 0
sao -06
0 60
~60 S
-J 40 0-c 0 ALBUQUERQUE (AC)
o 0 ALBUQUERQUE (PCC)
20 0 ag 13 ROCKLAND (ACIA MINNEAPOLIS-ST. PAUL IPCCI
00
0 20 40 so so 100 120 140ALLOWABLE LOAD, KIPS
LAYERED ELASTIC THEORY
Figure 19. Comparisons o~f allowable load on single wheelby PAVEVAL, DSM, and CER methods
1~00
CC 0A A
uJ U
400 *
I *O ~ 0 ALBUQUERQUE (AC)_3 0 ALBUQUERQUE (PCC)
4 200 0 ROCKLAND (AC)0 & MINNEAPOLIS-ST. PAUL (PCC)
000
ALLOWABLE GROSS LOAD. KIPS
DSM METHOD
a8 00C;A
td
0 r ;.j oz..:_o.
'uW 00- 2O 4O 6O 10
39 0 ALBUQUERQUE (AC)E A 0 ALB3UQUERQUE (PCC)
aqc 20 9 a ROCKLAND (AC)0A MINNEAPOLIS-ST. PAUL (PCC)
00 200 400 600 Soo 1000
ALLOWABLE GROSS LOAD. KIPSLAYERED ELASTIC THEORY
Figure 20. Comparison of allowable gross load onDC-8 aircraft by PAVEVAL, DSM, and CBR methods
43
O4
0ALBUQUERQUE (AC)JimU s 0 ALBUQUERQUE (PCC)
~~ ~~0 ROCKLAND(AC)
0 0
00
0 -2 4 6 8 10 12REQUIRED AC OVERLAY THICKNESS, IN.
DSM METHOD
10
z
00
01C * ALBUQUERQUE (AC)> 0 ALBUQUERQUE (PCC)
0 ROCKLAND (AC)a0 A MINNEAPOLIS-ST. PAUL (PCC)
2 --
0 2 4 10 12
REQUIRED AC OVERLAY THICKNESS. IN.LAYERED ELASTIC THEORY
Figure 21. Comparisons of required overlay thickness for
single wheel by PAVEVAL, DSM, and CBR methods44
. ..... .. .. ......
20-2O
81x -
1,- 9.
&SM MEO
12-
>Q
0 w ALBUQUERQUER(AC)
ALBUQUERQUE PE C)
13 ROCK LAND JAC)
0 6 a MINNEAPOLIS-ST. PAUL (PCCIge 00 000
a 0-wl 00
U/
0-0
0 II II
0 4 9 12 16 20 24REQUIRED AC OVERLAY THICKNESS, IN.
DSM METHOD
20-
0 w
X Z 0 ALBUQUERQUE (AC)
Ul 0 ALBUQUERQUE IPCC)
L RE120 ROCKLAND AC)SMINNEAPOLIS-ST. PAUL (PCCI
> 0
U A
3'5
0 0
0
0 4 8 12 16 20 24REQUIRED AC OVERLAY THICKNESS, IN.
LAYERED ELASTIC THEORY
Figure 22. Comparisons of required overlay thickness forDC-8 aircraft by PAVEVAL, DSM, and CB methods
45
E2 IS VARIEDEE, IS VARIED
EIS VARIED
'UU E, VARVIED
/ ,,,vWW PAVEMENT STRUCTURE/ / / ,ABOT WHCH VARITOS OF
1, h!"4 IN. E, - 460.000 PSI u, - 0.3
h2 . 10 IN.. E2 - 460.000 PSi v, - 0.3h3 i IN. E3 32000 PSI V3 -035
* E4 " 26.000 PSI 14 " 0.35
E. i,0p pi
Figure 23. Sensitivity study of allowable load
for AC pavement (case of strong base)
II I 1
8 o/ eu~c mE, IS VARIED
If IS VARIED BASIC PAVEMENT STRUCTURE40 ABOUT WHICH VARIATIONS OF
ELASTIC CNSTANTS ARE MADE
h, . 4 IN El .4 U.G PSI u1 - 03IS VARIED - 10 IN E, - 50MO PSI V2 -03 5
h3 IIN. E3 - 32001) PSI L, 035
Ed .26SOO PSi 4 -0 35
1 .t, P
Figure 2!.. Sensitivity study of allowable load
for AC pavements (case of weak base)
46/
moduli of the pavement layers. The layered elastic theory approach to
pavement evaluation predicts a very complicated dependence of the allow-
able load on the layered elastic structure of the pavement. Figure 23
shows the results for the case of an AC layer over a relatively strong
base layer, while Figure 24 illustrates the results for the case of ,3n
AC layer over a relatively weak base layer. The results for these two
cases are quite different because the limiting vertical strain in the
subgrade is manifested for the case of a strong base, while the limiting
tensile strain at the bottom of the AC layer tends to control for the
case of an AC layer over a relatively weak base.
The results of Figures 23 and 24 indicate that the layered
elastic theory and the prescribed limiting strain and stress conditions
produce a predicted allowable load-carrying capacity that is very sensi-
tive to the elastic properties of the pavement. In particular, under
some conditions the predicted allowable load may be a decreasing func-
tion of the Young's moduli of the pavement layers. This is due in some
cases to the fact that the limiting tensile strain at the bottom of the
AC layer is a decreasing function of the AC Young's modulus.14 ,1 8 For
instance, in Figure 24 the allowable load increases with the AC Young's
modulus up to a point where the decrease in the value of the limiting
tensile strain at the bottom of the AC layer begins to lower the allow-
able load.
47
Aimom
SUM4ARY AND CONCLUSIONS
SUMMARY
The capability of determining the load-carrying capacity of a
pavement and the overlay thickness required to upgrade a pavement is of
much importance to pavement engineers. A simple method of pavement
evaluation combining vibratory nondestructive field tests with a theo-
retical layered elastic formalism was developed to satisfy the needs of
the pavement engineer.7 The pavement evaluation and overlay design is
based on the subgrade Young's modulus value determined from vibratory
nondestructive testing and the subgrade Young's modulus value used in a
layered elastic theory computer program to calculate the allowable load-
carrying capacity and the required overlay thickness of a pavement.
Two computer programs, SUBE and PAVEVAL, are used to evaluate a
pavement based on the combined layered elastic theory and vibratory non-
destructive test approach. The computer program SUBE predicts the value
of the subgrade Young's modulus from the measured dynamic load-deflection
curves and the known values of the elastic moduli and thicknesses of the
pavement layers. The computer program PAVEVAL calculates the allowable
load-carrying capacity and the required overlay thickness based on the
layered elastic theory by relating the limiting stress and strain values
at points in the pavement or subgrade to the magnitude of the static
load applied to the pavement surface.
The validation of the results of the combined predictions of the
computer programs SUBE and PAVEVAL was obtained at three airport sites
and included AC and PCC pavements.
CONCLUSIONS
The theoretical and experimental work done fc, the validation
of the procedure of using the combined methods of vibratory nondestruc-
tive testing and layered elastic theory for calculating the allowable
load-carrying capacity and the required overlay tbickness of a Pnvement
yielded the following conclusions:
. ....
a. For the sites considered, generally poor agreement is obtainedbetween the values of the subgrade Young's modulus predictedby the computer program SUBE and the formula Es = 1500 CBR,and by extraction of the Young's modulus from the laboratoryresilient modulus measurements.
b. Although there is some scattering of data in comparing allow-able loads from PAVEVAL with the standard CBR method, thereis generally good agreement. As a matter of fact, the agree-ment between the PAVEVAL results and the CBR method is betterthan between the DSM method and the CBR method. The greatestscatter occurred with the AC pavements at Albuquerque andsome PCC pavements at Minneapolis-St. Paul.
c. Results from the overlay comparisons were not as encouragingas the allowable load comparisons. The PAVEVAL analysistended to predict thicker overlays than did the CBR method.
4~9
REFERENCES
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2. Green, J. L., "Literature Review - Elastic Constants for AirportPavement Materials," Report No. FAA-RD-76-138, Department of Trans-portation, Federal Aviation Administration, Washington, D. C.,1978.
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50
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