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OCR for page 407
APPENDIX H
MULTI-LA13 VALIDATION STUDY
.
H-1
OCR for page 408
APPENDIX H: MULTI-LAB VALIDATION STI)DY
INTRODUCTION
A multi-laboratory validation study was conducted as a part of the NCHRP I-28 study.
The primary purpose of the multi-lab validation program was to evaluate the proposed resilient
modulus calibration and test methods, given in NCHRP Interim Report No. 2 [Ho-, for asphalt
concrete, aggregate base and subgrade soils. Another benefit from the validation phase of the
study was a preliminary examination of the variation in resilient moduli obtained between
laboratories for similar materials. Because of tone and budget limitations, a full round-robin multi-
laboratory investigation, as described In ASTM E691-92 [H-2], was not conducted. A full round-
robin study would have involved 30 or more laboratories. Instead a more modest program was
undertaken involving a total of 10 laboratories.
ASPHALT CONCRETE
Introduction
The validation study for asphaltic mixtures was composed of (~) calibration of the testing
system using Free synthetic specimens and (2) resilient modulus testing of laboratory compacted
specimens provided by the reference laboratory. The two synthetic specimens had resilient moduli
of 145,000 psi and 556,000 psi. Both the MTS loading device and the new measurement system
developed in this study were used.
The following is a summary of the results from the three laboratories participating
In the study. These laboratories are designated as Lab I, Lab 2 and Lab 3. Lab ~ is considered
as the reference lab since they had considerably more experience performing diametral tests than
the other labs.
Analysis of Results
Figure H-! shows the graphical comparison of the mean values of resilient moduli
determined from the three laboratories. MR! and MR2 were obtained using calculated and assumed
Poisson's ratios, respectively. The use of the measured Poisson's ratio results in greater mean
resilient moduli values than those calculated using an assumed Poisson's ratio. A statistical
analysis was performed on the resilient modulus data, and Heir coefficient of variation are plotted
in Figure H-2. As shown on these two figures, the moduli determined from the calculated
Poisson's ratios show greater differences between the laboratories than those from the assumed
Poisson's ratio. Also, when the calculated Poisson's ratios were used in the computation, the
coefficients of variation from Lab 2 and Lab 3 are usually higher than those from Lab ~ (the
reference laboratory). These observations suggest that although the recommended testing system
and protocol yields better estimates of Poisson's ratio, the use of assumed Poisson's ratios gives
more consistent moduli. Figures H-1 and H-2 also show that He difference in resilient moduli for
calculated versus assumed Poisson's ratios is much smaller for the Lab ~ data than the Lab 2 and
Lab 3 data. This trend is probably due to the fact that the Lab ~ operator is much more
experienced In the resilient modulus testing of asphalt concrete using the proposed testing system.
H-2
OCR for page 409
5.0E+06
~4.0E+06
cn ~
_
o' ~
~ 3.0E+06
Cal
o
2.06~06
J
In
1.0E+06
O.OE+OG
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~4.0E+06
a,
_
, 3.0E+06
o
2.0E+06
u,
Al
1.0E+06
O.OE+OO
BASED ON MEASURED POISONS RATIO
_
_'
_]
D
_
Lab 1
Lab2
Labs
~ 1
104
41
77
TEMPERATURE (F)
BASED ON ASSUMED POISONS RATIO
41
Lab 1
Lab 2
Lab 3
h: , _: .
77
TEMPERATURE (F)
104
Figure H- 1. Comparl8On of Resilient ~o~lul1 for Different Labs
~-3
OCR for page 410
1.0
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RESILIENT MODULUS BASED ON
TESTED POISSONS RATIO
Or
.. . ~
.~
~ ,,ss
...~s
_~
~ .
..... .
. ...
.:
' ''"
, ~
Lab 1
_~
O_
Lab 2
Labs
41
77
TEIUPERATURE (F)
104
RESILIENT MODULUS BASED ON
ASSUMED POISSONS RATIO
Lab 1
rum
Lab 2
1 - -]
it_ - '1
Labs
.
I-..,'''-. 1
1 -
t:C;Xi~R
104
41
77
TEMPERATURE (F)
Figure H - 2. Comparison of Coofflcients of Variation for Different [08
H-4
OCR for page 411
Mean values of Poisson's ratio obtained from the three laboratories are given in Figure
H-3. In addition, their coefficients of variation are also plotted in Figure H-3. Lab ~ has the
smallest coefficient of variation among the three laboratories, again ProbablY due to the greater
level of experience of the Lab ~ technician.
r
o
Tables H-~(a), H-~(b) and H-~(c) provides a detailed summary of He resilient modulus and
Poisson's ratio for each lab at the temperatures of 41°F, 77°F and 104°F, respectively. Their
mean values, standard deviations and coefficients of variation are all given. Table H-2 gives a
summary of mean resilient modulus, Poisson's ratio and coefficient of variation for each lab at
three temperatures. hn general, the data from Lab 2 and Lab 3 show greater variation than those
from Lab 1. Regardless of the laboratory and the type of Poisson's ratio used, the coefficient of
variation at 104°F was the greatest, suggesting that greater caution has to be exercised when
interpreting the MR values determined from the indirect tensile test at high temperatures.
It is important to recognize in Table H-2 that the coefficient of variation in the Lab ~ data
was not affected much by using the calculated Poisson's ratios instead of the assumed values.
However, greater differences can be found with the Lab 2 and Lab 3 data. This finding suggests
that an experienced operator can produce equally or even more consistent MR values using
Poisson's ratios calculated from measured displacements. All the observations made earlier from
the graphical comparison were supported by the statistical analysis. Standard deviation of the MR]
values, based on calculated Possion's ratio values, was usually greater Han that of He MR2 values,
based on assumed Poisson's ratios. Again suggesting the importance of the operator's experience
on obtaining consistent resilient moduli values.
Statistical Comparisons. The findings from the graphical comparison were further checked by
performing the analysis of variance (ANOVA) tests with generalized linear models. The ANOVA
test procedure employs the F-value as the test static to test the null hypothesis that the resilient
modulus values at different temperatures are the same. The level of significance (p-value) for this
test is the probability of having F-value larger than the calculated F-vatue from a data set for the
~ . . .. . .. . ~ , . . . . . . .
factor in question. A smaller value ot tills probablllty unpiles the heavier weight of the sample
evidence for rejecting the null hypothesis, and thus, in this investigation, more likely that the
resilient moduli are different. A typical criterion of using a critical p-value of 0.05 was employed
in this study.
Table H-3 summarizes the statistical results on the possible effect of operator-to-operator
variation, as well as the effect of fresh and re-tested specimens. Specimens TI, T2,..., T6 were
tested first In Lab I. Then, specimens TI, T2 and T3 were tested again at Lab 2, and specimens
T4, T5, T6 at Lab 3. Table H-3(a) compares results obtained by Lab ~ with Lab 2 and Lab 3.
For the same group of specimens, the p-values of resilient moduli obtained from the assumed
Poisson's ratios are usually higher than those from the calculated Poisson's ratios, which indicates
that the calculated Poisson's ratio signifies the lab-to-lab variation.
Tables H-3(b) and H-3(c) compare the results between fresh specimens (i.e., TI, T2, ....
T6 at Lab ~ vs. TI, T2, ..., T6 at Lab 2 and Lab 3, respectively. These tables, indicate that p-
values are higher for fresh specimens than revested specimens. This implies possible damage of
the re-tested specimens regardless of the variation between operators. Therefore, structural
changes during the proposed MR tests are more significant than the lab-to-lab variation.
The statistical analysis was performed on a very limited number of samples, making the
interpretation of the statistical results less reliable. An extensive validation study is recommended
to obtain better evaluations on sample-to-sample and lab-to-lab variations.
H-S
OCR for page 412
1.5
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labs
Labs
1 _e_
41
77
TEMPERATURE (F)
104
POISONS RATIO
__
-
Id:=
...
'."'." :
~ . .
~ ,..2.',.:...
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eel 1 i1 ~
41
77
TEIYIPERATURE (F)
Lab1
Lab 2
Cod
Lab 3
104
Figure H - 3. Co~arison of poisson's Ratios for Different Lobe
H-6
OCR for page 413
Table H-~. Comparison of Resilient Moduli and Poisson's Ratio for the Different Labs
(a) 4IoF
Spec~nen
Tl
T2
T3
T4
TS
T6
Ul
~2
U3
U4
US
U6
Avcragc
Std. dev.
Coef. Var.
Speci~ er
T1
-T2
T3
T4
T5
T6
U1
U2
U3
U4
U5
U6
Ave~gc
Std. dev.
Coef. Var.
Specimcn
T1
T2
T3
T4
TS
T6
Ul
U2 .
U3 .
U4
US
U6
Averagc
Std. dcv.
Coef. Var.
Poi~n's Ratio
(c) 1040 F
,
Poisson's Ratio
Lab 1 ~ Lab 2 ~ Lab 3 Lab 1
0.72 0.18 2.94E+S
. .
0.68 0.39 4.69E+5
.
0.56 0.28 2.43E+S
0.70 0.86 2.79E+S
0.56 1.02 392E+5
0.57 ~1.4S 2.28E+5
0.41
0.30
. .
0.37
1.29
1.11
1.15
0.63 1.15 0.32 3.18E+S
0.07 0.19 0.08 8.56E+4
.
0.11 O.t6 0.24 0.27 _
Resilient Modulus (~t')
Lab 1
2.02E+6
2.13E+6
2.11E+6
2.00E+6
2.21E+6
2.25E+6
2.12E+6
9.08E+4
0.04
:
(b) 770 F
Lab2
4.26E+6
4.78E+6
2.61E+6
8.63E+6
2.68E+6
1.25E+6
4.04E+6
2.36E+6
0.58
Lab3
1.62E+6
1.13E+6
1.83E+6
.
1.39E+6
9.32E+S
1.19E+6
1.35E+6
3.03E+S
0.22
Resilicnt Modulus (M, )
Lab 2
.
1.31E+6
2.30E+6
1.26E+6
1.96~+6
1.23E+6
l.l9E+6
1.54E+6
4.30E+S
0.28
Lab3
6.22E+5
5.67E+S
5.64E+5
6.62E+5
5.28E+5
5.29E+S
S.79E+S
4.88E+4
0.08
Resilient Modulus (~t')
_ Lab 2
3.50E+S
8.07E+S
6.18E+S
5.26E+5
S.4SE+5
4.67E+5
S.52E+S
1.40E+S
0.25 .
H-7
.
Lab3
1.85E+5
5.03E+5
3.97E+S
2.58E+S
1.71E+S
1.63E+5
2.80E+S
1.28E+5
0.46
Lab I _
1.44E+6
1.55E+6
1.42E+6
1.57E+6
I.85E+6
1.59E+6
1.57E+6
1.40E+S
0.09
- ~;~
Lab 2 | Lab 3
1
1 l.41E+6
1
1 1.45E+6
T l.25E+6
1
1.94E+6 1
. _- 1 -
1.64E+6
1.S4E+6 |
~3iE~
11
1.13E+6
~ 1 1.23E+6
1.93E+6
1.65E+6
1 - 1
1 2.09E+6 1
1 1.BOE+6 1 1.31E+6
1 1
1 2.00E+S 1 1.13E+5
1 011 1 o.og
Rcsil~ent Modulus OM`~) |
Lab I I Lab2 I Lab3 1
1 1 1
8.17E+5 1 1 6.71 E+S 1
1 1 ~
~.1 IE+S~
7.95E+S 1 T 5.8BE+~
7.15E+5 1 5.20E+S 1 1
1 1 . ~
8.91E+5 1 9.70E+5 1 1
~1 -~
8.47E+S 1 5.21 E+S 1
| 1 6.17E+S
I 1 5.48E+5
1 1 5.84E+5
1 ~
- 1 6.08E+S
~1 5.30E+5
T | S.80E+S 1
1 8.23E+5 1 6.21 E+S 1 6.20E+S
~1
1 5~82E+4 1 1.59E+S I 5.53E+4
1 1 1
L 007 1 026 1 o.og
Resilient Modulus (M' )
Labl
2.32E+5
3.83E+5
1
2.26E+5
2.21E+5
3.63E+5
2.09E+5
l
l
2.72E+S
7.17E+4
0.26 _
Lab 2__~
1
1
2.40E+5
4.91F,+S
2.75E+5~
1
1
2.60Eff
3.06E+5
2.54E+S
3.04E+5
8.60E+4
0.28
Lab3 |
3.16E+S
5.87E+S
5.60
1
l
2.61 E+S~
1
2.33E+5 1
. ~
1.96E+5 1
1
1
1
_3.64E+S - |
1.53E+S
0.42
OCR for page 414
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OCR for page 415
UNSTABILIZED AGGREGATE BASE EXPERIMENT
Introduction
The aggregate base multi-laboratory resilient modulus validation testing program involved
4 different laboratories. A fifth laboratory was to have participated in the experiment, but their
testing equipment could not be set up in time. The validation study consisted of two parts: (1)
system calibration, including using aluminum and polymer specimens, and (2) the testing of 3
different aggregate base materials. The specimen preparation and testing procedures used in the
experiment are given in NCHRP 1-28 Interim Report No. 2. The tentative test procedure required
the use of two EVDTs mounted outside He biaxial cell to measure axial deformation. The testing
procedures, except as noted, were reasonably similar to those given in the SHRP P46 (November,
1989 procedure).
The resilient modulus mode} used in the multi-laboratory study is as follows:
M =KI ~K2 oK3
R d
where MR
_ _ _
K1,K2,K3
= resilient modulus
= bulk stress (~ 02 03)
= deviator stress
= model constants
(H-1)
Mode! constants were evaluated by multiple regression analysis techniques. The statistical analyses
employed in this study were performed using the general techniques described in Chapter 2 for the
aggregate base study.
Materials and Notation
Base Materials. The 3 different nonplastic aggregate materials tested in the multi-laboratory study
are described as follow:
Base Notation Description
Base ~ B!
Base 2 B2
Base 3 C4
Well graded, nonplastic fines, I.5 in. maximum size,
subangular to angular crushed stone. Four percent fines.
Specimen compacted to 100 percent T-~80 density.
Well graded, nonplastic, 1.25 in. maximum size,
subangular to angular crushed stone. Ten percent fines.
Specimen compacted to 100 percent T-~80 density.
Well graded, nonplastic Minnesota DOT Class 4 base
material with partial crushing of faces.
H-9
OCR for page 416
Representative samples of aggregate for specimen preparation were thoroughly mixed to
a homogenous condition, and then split into the required quantities following accepted sampling
practices. Sufficient material for two extra labs were prepared at the same time and held in
reserve. The samples sent to each laboratory were selected using a random number procedures.
The samples were placed in 5 gal. buckets, labeled, sealed and shipped to each laboratory.
System Calibration. Preliminary system calibration consisted of evaluating the testing system
alignment and extraneous deformation in the testing system. Extraneous system deformation was
evaluated using an aluminum cylinder 12 in. high and 6 in. diameter which simulated a specimen
of essentially rigid material. Preliminary calibration procedure used is given in Appendix D.
Final calibration was achieved using a stiff and a soft synthetic polymer specimen. These
reference specimens were shipped to each lab. The two synthetic specimens used have a known,
nominal resilient modulus of 8,000 psi and 50,000 psi. These specimens are the same synthetic
specimens as used in the laboratory base study described in Chapter 2 of this study. The specimen
having a stiffness of 50,000 psi is representative of an unbound aggregate base subjected to a
relatively high bulk stress (~) of about 45 to 55 psi. The soft specimen with a resilient modulus
of 8,000 psi is representative of a typical unbound aggregate base subjected to a low bulk stress
of about ~ to 10 psi.
Steel top and bottom plates were epoxy glued to the ends of the 50,000 psi synthetic
specimen to avoid cupping of the ends with use of the specimen. Cupping of the end of the
synthetic Type ~ base specimens used in the SHRP program was a serious problem. Unfortunatelv.
One steel end cap was knocked off the specimen as it was moved between labs.
_ _ ,,
Notation. The notation described here is used on the tables and figures given in subsequent
sections. The four laboratories included in the study are indicated as Ll, L2, L3 and L4. Lab ~
was used as the reference laboratory since good agreement In resilient moduli values was obtained
from axial displacement measurements made using external EVDTs and inside clamp supported
EVDTs. The three bases tested, which are described above, are designated as BI, B2 and C4.
The two replicate specimens of the same material prepared and tested by the same lab are indicated
by A and B. Therefore, the notation "DEBRA" on a figure or table indicates (Base 2 (i.e., B2)
which was tested by Lab 2 (i.e., L2) and the results are for the "A" specimen. The notation
"~3BlAB" indicates lab 3 (i.e., L3) tested Base ~ (i.e., Bl) and the data for both the A and B
specimens have been combined and the results presented.
Resilient Modulus Test Results
Within Lab Reproducibility of Test Results. To perform reliable resilient modulus tests, the test
results for a specific laboratory (and a single test apparatus and operator) must be reproducible for
replicate specimens of the same material and the same method of specimen preparation. Figures
H-4 and H-5 illustrate the typical variability observed between replicate specimens of the same
material prepared and tested by the same lab. As shown on the figures, 3 different values of
deviator stress were applied in the resilient modulus test for each of the 5 values of confining
pressure used. The 95 % upper (UL`) and lower (Lid) confidence intervals for the replicate pair of
tests are shown on the figure in addition to the actual test points for each of the two tests.
The consistency comparisons for replicate specimens given in Table HA are for a 90%
confidence level and are based on a comparison of the individual model constants KI, K2 and K3.
H-10
OCR for page 417
1oo
go
80
~0
60
~0
~0
30
20
10
o
=
_
LEGEb D
A: L1 B2A
+ L1 B2B
o LID
~ UL
: =
_
_
_ , +x ~
_+~.
.
LL = Lamer 95 °~6 Confidence Umits
UL = Upper 95°h Confidence Um~ts
0 20 40 60 80 100 120
Bulk Stress, ~ (psi)
Figure H4. Companson of Resilient Moduli for Replicate Specimens- Lab
do
3S
._
tax
~ 26
-
o
c
-
30
20
16
10
o
LEGEND
S L2B1A
~ L2BiB
-O- LL
- ~ UL
B ~'
4'. I'
:
o
ALL 1 1 ~
C
pit $.
I. O
l iaA~
. ~ \,rO~.~
,0-'~ ,#0'
' O'
U = Lower 95 % Confidence Umits
UL = Upper 95% Confidenoo Umits
_
0 20 40 60
Bulk Stress, 8. (psi)
80 100
Figure H-S. Compar~son of Resilient Moduti for Replicate Specimens- Lab
H-11
A: a3 - 3 PSI
B.: CT3 ~ S PSI
C: ~3 2 10 PSI
D: CS3 - IS PSI
E: O3 ~ 20 PSI
A: CS3 = 3 PS]
B: CT3 3 S PSI
C: O3 = 10 PSI
D:~3= lSPSI
E: a3 - 20 PSI
OCR for page 424
80
70
60
, 60
g 40
E 30
-
o
20
10
0 20 lo
Q
LEGEb D
~ L282
O LL(L1 B2)
- +U4L1Bz}
D
E
~:
IAF
LL - LaNot 95 * Confidenos Um~
UL = Upper 85% Confidence Limits
- 1- ~ 1- 1
60 80 t 00 120
Bulk Stress, 8, (psi)
A: CI3 ~ 3 PSI
B.: O3 ~ S PSI
C: O3 ~ 10 PSI
D:~3~1SPSI
E: O3 ~ 20 PSI
Figure H-6. Compar~son of 95% Conf~dence L~mit Mode! Fit of Lab ~ MR Results with
Lab 2: Base B2
120
~o
~oo
^ 90
E 80
, 70
60
0
-
._
~0
40
30
20
10
O
0 20
.
. _
_
LEGEND
· ~ - - L4B2
O LL(L1 B2)
O UL(L1 B2)
l
je:
1' 1
1
.11
. 1
1 _
r.,.
..,~
1 ~
Lab L4
1
u
Rcferencc Lab L1
LL = Lower BS % Confidence
Limits
1
1 1 1 1
40 60 80
Bulk Stress, 8, (psI)
100 120
|A CI3 = 3 PSI
B: O3=SPSI
;C:CS3 5IO PSI
D: CT3 = IS PSI
E: O3=20PS!
Figure H-7. Companson of 95% Conf~dence L~mit Mode! Fit of Lab ~ MR Results with
Lab 4: Base B2
H-18
OCR for page 425
80
70
~ 60
x
-
~ 50
-
E 4o
-
~ 30
-
20
10
o
LEGEND
- L3B2
LL(L1 El2)
U4L1 B2)
Reference
L1
Lab
B
lAB
L3
Ma
LL = L DW" 95 % Confidence Limil s
UL = Upper 85% Confidence Limits
.! ~ ~
0 20 40 60
Bulk Stress, 8, (psi)
A: tS3 = 3 PSI
B: C,3 - S PSI
C: O3 = 10 PSI
D:~3= Is PSI
E: c53 = 20 PSI
80 100 120
Figure H-8. Comparison of 95% Confidence Limit Model Fit of Lab 1 MR Results with
Lab3:BaseB2
H-19
OCR for page 426
Not all laboratories carefully follow calibration and/or testing procedures. This
error in several instances In the multi-lab study lead to inaccurate resilient modulus
test results.
For the same operator and test equipment, reproducible resilient moduli for
replicate specimens can be obtained using the aggregate base specimen preparation
and testing procedures.
When axial deformations are measured outside of the biaxial cell, equipment
calibration becomes a dominating factor in obtaining reliable resilient modulus
results. The required {eve! of equipment calibration is complicated and time
consuming. The results of this multi-lab study, although admittedly of limited
scope, cast serious doubt as to whether most production type labs (or even
research labs) have the required expertise and are able to expend the necessary
time and effort to achieve accurate resilient modulus results using externally
mounted EVDTs.
5.
REFERENCES
The multi-laboratory study shows the need for measuring axial deformation, which
is used to calculate the resilient modulus, directly on the specimen rather than
outside of the biaxial cell. Measurement of axial deformation on the specimen
makes the measured resilient modulus considerably less sensitive to sysem
calibration than when externally mounted EVDTs are used.
Hal. Barksdale, R. D., Alba, I., Khosla, P. N., Kim, R., Lambe, P. C., and Rahman, M. S.,
(1993), Laboratory Determination of Resilient Modulus for Flexible Pavement Design,
Interim Report No. 2, Prepared for NCHRP Project I-28, Georgia Tech Project E20-634,
Atlanta, GA, 445p.
H-2. ASTM, (1992), "Standard Practice for Conducting an InterIaboratory Study to Determine
the Precision for Test", Designation E691-92, American Society for Testing and Materials.
H-20
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SUBGRADE COHESIVE SOIL EXPERIMENT
Introduction
The subgrade cohesive soil multi-laboratory validation resilient modulus testing program
involves! 3 different laboratories. A fourth laboratory was to have participates] but the laboratory
director resigned before the tests could be completed; without him the lab could not perform the tests.
The participating laboratories measured cyclic deformations using LVDTs located inside the biaxial
cell ant! therefore did not complete the detailed calibration program described in Appendix D. Each of
the labs used the loading schedule proposed in Interim Report No. 1 for NCHRP I-28; they used their
own specimen preparation procedure and equipment setup. Since eventually resilient modulus tests will
be performed on unclisturbed samples, it was expected that experimenters could obtain He most
consistent specimens by using their own well developed laboratory compaction procedures.
Materials and Notation
Cohesive Soils. Samples of two air dried North Carolina subgrade soils were supplied to the 3
laboratories in 5 gallon white plastic buckets at the end of summer, 1994. Figure H-9 shows the T-99
compaction curves along with the Atterberg limits for each of these soil samples. Sample No. 13
classifies as an A-5 and sample No. 14 classifies as an A-7-5. Based upon the T-99~curves the
laboratories were directed to prepare specimens at the optimum water contents ant! maximum dry
densities as shown in Table H-8; reported results indicate that the No.13 specimens dried by up to
1.3% and that the No. 14 specimens ciriecl by up to 4.3% cluring compaction.
Table H-8. Specimens Tested
Lab Specimen w SO ad, pcf
Specified 13 18 ~96.9
L1 ~13A 17.4 98.2
13B 17.4 98.2
13C 17.4 98.2
L2 13 17.5 92.8
L3 13A 16.9
13B 16.7
Specified - 14 25 93.8
L1 14A 25.4 94.3
14B 25.5 95.6
14C 25.5 95.6
L2 14 24.2 92.3
L3 14A 20.7
_ 14B 23.5
H-21
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Notation. The three laboratories are called Ll, L2, and L3 and the specimens are referenced by soil
sample number and a following letter. For example Ll-13A represents the first test performed on soil
sample No. 13 by laboratory L1. Laboratory Ll ran three tests on both soil samples No.13 and No.
14, laboratory L2 ran only one test on each soil sample and laboratory L3 ran two tests on each soil
sample.
In contrast to the aggregate base experiment, He laboratories participating in the subgrade soil
experiment did not perform a calibration testing program. While requested to perform such testing He
technicians were unprepared and when testing fell well behind schedule they completed just He
requested tests.
Resilient Modulus Test Results
Figures M-IO, H-~! and H-12 portray the test results measured by the three laboratories
plotted as resilient modulus in ksi versus deviator stress in psi. Each test involved 15 load sequences of
100 cycles at all the combinations of five different deviator stresses and three different confining
stresses. Figure H-IOa shows that with the exception of a confining stress equal to 4 psi on specimen
13B confining stress had little influence on the measured resilient moduli for No. 13. Figure H-IOb
also shows no dependence of resilient modulus on confining stress for No. 14 but has an unexpected
rising resilient modulus with confining stress at ~ and 2 psi confining stress. The No. 14 specimens had
much higher resilient moduli than the No. 13 specimens so the vertical scales had to be increaser! by a
factor of S. Figure H-} ~ shows the test results for laboratory L2 with similar qualitative patterns but
resilient moduli for No. 13 about 2 times larger than L1 and for No. 14 about 1/2 as large as Ll.
Figure H-12 shows that L3 measured resilient moduli 10 to 20 times smaller than either Ll or L2. It
appears L3 has some systematic error which should have been discovered during a calibration test
program.
Table H-9 summarizes the statistics for the subgracle testing program baser! upon the model:
MR = K ~ by,] O
These results suggest poor agreement Motif within each lab and for lab versus lab. Variability in tested
specimens, and not just the testing procedure, contributed to the observed variability. An effective
calibration program using synthetic specimens would help identify tl~e source of errors.
General Findings
Poor resilient modulus results were obtained while specifying soil compaction at the optimum
water content which should produce the most consistent specimens. Problems getting the tests performed
indicated that each of the three laboratories were experiencing significant trouble just getting the test
equipment operational. The sophistication of the electronics and the difficulty to visually observe tile
behavior mean tint a greater level of care is required to obtain meaningful values. Because the subgrade
soil specimens are softer than tile other pavement materials, they can be damaged while setting up the
specimen for testing. Before actually testing subgrade specimens, tile participating laboratories need to
subunit to a well planned and supervised calibration program using synthetic specimens. In addition some
of the equipment used by these laboratories does not uncork as advertised, an] their technicians have too
little experience to identify the source of problems.
H-22
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Table H - 9. Summary of Statistics for Subgrade Soil Testing
Lab Specimen K1 K2 K3 R2 s Avg. CV%
. .
L1 1 L1-13 1 1.737 ~.114 0.177 1 0.877 0.078
L1 -13B 0.725 -0.586 0.769 0.89S 0.134
L1 -13C 1.946 -0.293 0.162 0.874 0.082
Average 1.469 4.331 0.369
~ 0.653 0.238 0.346
CV~ 44.442 72.054 93.666 70.0S4
L1 -14A 30.399 0.091 -0.009 0.378 0.09
L1-14B 39.615 -0.084 0.011 0.241 0.09
L1 -1 4C 30.122 0~085 ~OeO01 0.289 0.089
Average 33.379 0.031 0.000
~ 5~403 0.099 0.010
CV% 16e 186 322~868 5076~662 1 80S.239
LZ 4 1 1~448 -0~241 0~483 T 0~928 0~058 1
~ 1 30~517 -0~269 0~002 1 0.791 ~ 0.11 1 ~
.
L3 L3-13A 0~307 -0~456 -0.112 0~911 0.1 31
L3-t 3B 0~288 -0~446 -0~089 0~866 0.159
Average 0.297 ~.451 -0.100
~ 0~013 0~006 0~016
CV% 4~474 1~427 15~870 7~257
0~790 -0~017 0~105 1 0~133 0~118 |
L3-1 4B 0~576 -0~249 0~459 0~612 0.163
Average 0.683 -0. 133 0.282
~ 0.151 0.164 0.250
CV% 22e 147 123~239 88~611 77~999
H-23
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Sam le LL -#40, % -#200, % G
#13 45 5 87 44 2.77
#14 58 25 82 63 2.67
'°°T~ At- ~ ------ ~
- ~ ' 1 - 1 " 1 \\ 1 G = 2 72
;=Sample#~] ~ p
90 1 ~ ~ | ~ it Sample#14 ~ ~ l
1 ''-''-'''''''---1-'''-''''-':'--- ''- - ''''1''''- '''-''' /' ·1'''''---'' -'-'-'-' ''--1'''''--'-' ' ''-' -'' 1 ''''\\'~"''-'- '
1 '- '-'''''"'''''---''''''-- -'1 '--'''''-''-''-'-' '-"'''-''''''-"1 "--'--''''/ i''''-''' '' '1'-'' ''-''' -:---'2'' '"'"'''' ' '1"' ' ' ' '''' ' -'''' '''1' '''' '\'''' '' -'-''
1 ' ' ' -'''' - ----' - '-1 '"' " '''--I ''--- ''"'-'-'I 1 1 ~ - 1 ~' ' '1' ' ' - '"' -~''i' ""----'''' '- 1
. . I ., :
85
5 1 0 1 5 20 25 30 35
Water Content, oh
Figure H - 9. Cohesive Soil Samples used for Subgrade Tests
H-24
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6- ~
~ -
cO
4-
in
o3
- 2
_
a)
a:
1
o
50
40
.
co
x
in
~5 30 _
O
ID 20-
e_
co
~ 10
-
~0
~ 0~
-
-
O
o
, . . .
.
.
*
· ·,
O 4 psi (A)
~ 2 psi (A)
0 1 PA (A)
4 psi (B)
2 pal (B)
1 psi (B)
x 4 psi (C)
+ 2 psi (C)
* 1 psi (C)
_ ~I l I ~ I ~ r I T I I 1
0 5 10 15
Deviator Stress (psi)
(a) Results for L1-13
0 4 psi (A)
~ 2 pSi (A)
0 1 PA (A)
4 psi (B)
2 pSi (B)
1 psi (B)
4 psi (C)
2 pSi (C)
*
l
5 . 10 15
Deviator Stress (psi)
(b) Results for L1-14
Figure H - 10. Subgrade Soil Test Results for Lab 1
H-25
OCR for page 432
6
5-
.^
ye
_,
AL _
an ~
~3
a)
._ ~
_ ~ _
·_ _
a)
a:
1
O
50
40
._ .
_
an
~5 30
0
20
t
a)
·_
._
tar:
10
O O
~O
O 4 psi
~ 2 psi
0 1 psi
O O 0
A
O ~
r I I I T
I - 1 1-- 1 -
0 5 10 15
Deviator Stress (psi)
(a) Results for L2-13
-
O 4 psi
~ 2 psi
0 1 pad
1~
10 15
-
O-
o
5
Deviator Stress (psi)
(b) Results for L2-14
Figure H - 1 1. Subgrade Soil Test Results for Lab 2
H-26
OCR for page 433
0.6 - l
0.5
_`
in .
,,, 0.4
0.3
:-0.2
~n
A:
0.1
O- ,
o
to
18
I\ A
IF ~-
O 4 psi (A)
2 psi (A)
1 psi (A)
4 psi (B)
2 psi (B)
1 psi (B)
. ~
5 10 15
Deviator Stress (psi)
(a) Results for L3-13
4
· _
_'
in
:,3
O
~
~ 2
a)
._
._
In
tr:
1- .
o
_ _
~ ~ -e
-
,- l l l
o
r I I 1
O 4 psi (A)
~ 2 psi (A)
0 1 psi (A)
4 psi (B)
2 psi (B)
1 psi (B)
1 1 1
() 5 10 15
Deviator Stress (psi)
(b) Results for L3-14
Figure H - i2. Subgrade Soil Test Results for Lab 3
H-27
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Representative terms from entire chapter:
resilient moduli
