1290
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
5 CONCLUSIONS
analysis (Ishikawa et al. 2012), at an actual Japanese pavement
structure. The elastic moduli (
E
2(FWD)
) for subbase course layer
calculated from FWD test results using the static back-analysis
program BALM (Matsui et al. 1998) are also plotted against the
volumetric water content (
θ
) measured at the long-term field
measurement (Figure 7).
2010/09/01
2010/12/01
2011/03/01
2011/06/01
2011/09/01
0
5
10
15
thawing
regular
freezing
regular
Amount of precipitation (mm)
Volumetric water content,
Date (day)
r0
=9.13%
Subbase course
D
c
= 94.2%
0
30
60
90
120
150
Figure 7. Results of long-term field measurement
0 5 10 15 20 25 30
0
50
100
150
200
250
300
opt
CBR test results
withAASHTO(2008):
:
N
f
=0 cycle
:
N
f
=1 cycle
:
N
f
=2 cycle
Resilient modulus,
M
r(CBR)
(MPa)
Volumetric water content,
r
Figure 8. Resilient modulus estimated from CBR test results.
The following findings can be mainly obtained:
–
Two new test apparatuses have high applicability in the
evaluation of the deformation-strength characteristics of
granular base course materials exposed to repeated freeze-
thaw and concurrent seasonal fluctuations in water content.
–
A dominant effect for mechanical behavior of base course
materials in cold regions is a decrease in the CBR and the
resilient modulus with increasing water content and freeze-
thaw action, and with decreasing confining pressure.
–
Empirical formulas adopted in AASHTO standards have
sufficient applicability in evaluation of resilient modulus of
subbase course layer in Japanese pavement structures.
–
Decreasing tendencies of resilient modulus against water
content derived from MR tests, CBR tests, and FWD tests
qualitatively and quantitatively agree well with each other.
These indicate that when developing a theoretical model for
predicting the mechanical behavior of pavement structures in
cold regions, it is important to give a special consideration to
the degradation in the bearing capacity and resilient modulus
caused by cyclic freeze-thaw actions even in non-frost
susceptible granular base, in addition to the effects of an
increase in water content during the thawing season. However,
further examination of the validity, limitation of application and
so forth needs to be conducted in the future in order for the
outcomes of this research to be practically applicable.
6 ACKNOWLEDGEMENTS
This research was supported in part by Grant-in-Aid for
Scientific Research (B) (20360206 & 23360201) from Japan
Society for the Promotion of Science (JSPS) KAKENHI.
7 REFERENCES
M
r
=17.6·CBR
0.64
(AASHTO 2008)
(2)
The decreasing tendencies of all types of
M
r
with increasing
water content are in fair agreement with each other, irrespective
of the calculation method. Though
M
r(MR)
noticeably depends on
σ
c
'
in case of the same water content,
M
r(MR)
estimated at
σ
c
'
of
10 kPa closest to the in-situ overburden pressure is almost equal
to the upper limit of
E
2(FWD)
. Besides,
M
r(CBR)
approximately
coincides with
M
r(MR)
when the principal stress ratio (
σ
'
1
/
σ
'
3
) is 4
under the
σ
'
c
of 10.0 kPa, irrespective of
θ
. Accordingly, it
seems reasonable to conclude that the suction-controlled MR
test results in this research quantitatively match those in
previous laboratory element tests and field measurement, and
that Eq. 1 adopted in the AASHTO standard has high
applicability in the evaluation of the resilient modulus of
subbase course layer in Japanese pavement structures.
AASTHO. 2003. Standard Method of Test for Determining the Resilient
Modulus of Soils and Aggregate Materials. AASTHO Designation
T 307-99.
Standard Specifications for Transportation Materials
and Methods of Sampling and Testing
, T307-1-T-307-41.
AASHTO. 2008.
Mechanistic-Empirical Pavement Design Guide: A
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Ishikawa, T., Kawabata, S., Kameyama, S., Abe, R., and Ono, T. 2012.
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Figure 8 shows the relationships between
M
r(CBR)
and initial
volumetric water content (
θ
) under different
N
f
. Note that the
range from residual volumetric water content (
θ
r
) to
θ
opt
correspond to optimum water content obtained from a water
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2012) is indicated in the figure. The overall tendency is
identical to that observed in Figure 4. When being focused on
the range, a decrease in
M
r(CBR)
due to the increase in the
number of freeze-thaw process cycles is severe as compared
with a decrease in
M
r(CBR)
due to the increase in water content.
Besides, according to results of long-term field measurement
(Figure 7), it is expected that the resilient modulus of subbase
layer at the actual pavement structure deteriorates along the path
shown by the arrows in Figure 8 when it is exposed to repeated
freeze-thaw and the concurrent seasonal fluctuations in water
content. Therefore, freeze-thaw action seriously influences the
resilient deformation characteristics of granular base course
materials and hence it also affects the fatigue life of pavement
structures in cold regions.
Japanese Geotechnical Society. 2003. Test method for frost
susceptibility of soils (JGS 0172-2003).
Standards of Japanese
Geotechnical Society for Laboratory Soil Testing Methods
, 45-50.
Japanese Standards Association. 2009. Test Method for the California
Bearing Ratio (CBR) of Soils in Laboratory (JIS A 1211: 2009).
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. (in Japanese).
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