analysis of variations of pavement subgrade soil water content 1 andrew g. heydinger, ph.d., p.e....
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Analysis of Variations of Pavement Subgrade Soil Water Content
1Andrew G. Heydinger, Ph.D., P.E.and
2B.O.A. Davies
1Professor and 2Former Graduate Student
Department of Civil EngineeringThe University of Toledo
Toledo, Ohio
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Purpose of Research
• To analyze the long term pavement performance (LTPP) climatic data in the Federal Highway Administration (FHWA) database, DataPave, for the seasonal variations of pavement subgrade soil volumetric water content.
• To infer impacts of the seasonal variations of moisture on pavements by considering the effects of subgrade moisture content on subgrade soil resilient modulus.
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Significance of Research
• Water content or degree of saturation is used to compute resilient modulus for unsaturated subgrade soils in the Mechanistic-Empirical Pavement Design Guide (M-EPDG) that was developed for the FHWA.
• Since a mechanistic approach is taken, it is necessary to know the variations of material properties.
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Resilient Modulus
Empirical equation proposed in the M-EPDG.
Where a, b, and ks are material parameters.
Values for the parameters are recommended in
the M-EDG for coarse and fine-grained soils.
))(exp( log
optsRopt
R
SSka
aba
M
M
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Seasonal Monitoring Program (SMP)
63 Sites with Seasonal Instrumentation
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Four Climatic Regions
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SMP Instrumentation
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TDR Moisture Measurements
Results of laboratory testing on fine-grained soils by Klemunes (1998).
R2 = 0.6841
0
10
20
30
40
50
60
0 10 20 30 40 50 60
Laboratory Volumetric Water Content (%)
Pre
dic
ted
Vo
lum
etr
ic W
ate
r
Co
nte
nt
Pre
dic
ted
by T
op
p's
Eq
uati
on
(%
)
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TDR Moisture Measurements
Field and laboratory tests on a fine-grained soil (Heydinger and Randolph, 1998).
R2 = 0.3716
0
5
10
15
20
25
30
0 5 10 15 20 25 30
Laboratory Gravimetric Water Content (%)1Computed assuming gdry = 108 lb/ft3
1 TD
R G
ravim
etr
ic W
ate
r C
on
ten
t (%
)
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PCC Section in Ohio
28
32
36
40
44
7/1/96 7/1/97 7/1/98 7/1/99 7/1/00 7/1/01 7/1/02Date
Vol
umet
ric W
ater
Con
tent
(%)
-20
0
20
40
60
80
100
Ave
rage
Soi
l Tem
pera
ture
(o C)
Average VWC, TDR 2,3,4 Average Soil Temperature
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AC Section in Ohio
32
36
40
44
7/96 12/96 7/97 12/97 7/98 12/98 7/99 12/99 7/00 12/00 7/01 12/01 7/02
Date
Vol
um
etric W
ater
Con
tent (%
)
-10
10
30
50
70
90
110
130
150
Ave
rage
Soi
l Tem
per
ature
o C
Average TDR 1, 2, 3 Computed Water ContentAverage Soil Temperature
VWC(t) = 37.1 + 1.66 sin[2π/365.25(t-130)
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VWC and Precipitation for AC Section
0
5
10
15
20
25
30
35
40
45
50
07/01/96 07/01/97 07/01/98 07/01/99 07/01/00 07/01/01Date
Vol
umet
ric M
oistur
e C
onte
nt (%
)
0
10
20
30
40
50
60
70
80
90
100
Pre
cipi
tatio
n (m
m)
1 2 3 4 10 Precipitation
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WF Sections, Coarse-Grained Soil
6
10
14
18
22
26
30
7/1/93 7/1/94 7/1/95 6/30/96 7/1/97
Date
Vo
lum
etr
ic W
ate
r C
on
ten
t
91803 231026 251002 271018 271028 404165
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WF Sections, Fine-Grained Soil
20
24
28
32
36
40
44
48
7/1/93 7/1/94 7/1/95 6/30/96 7/1/97 7/1/98 7/1/99 6/30/00 7/1/01
Date
Vo
lum
etr
ic W
ate
r C
on
ten
t
204054 390901 390204 833802
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WNF Sections, Fine-Grained Soil
20
24
28
32
36
40
44
07/01/94 07/01/95 06/30/96 06/30/97 07/01/98 07/01/99 06/30/00 06/30/01 07/01/02
Date
Vo
lum
etr
ic W
ate
r C
on
ten
t
133019 370201 370205 370208 510114
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WF Sections, Coarse-Grained Soil
0
5
10
15
20
25
30
Vo
lum
etr
ic W
ate
r C
on
ten
t
Minimum Maximum
0.0
0.5
1.0
1.5
2.0
MR/M
Ro
pt
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WF Sections, Fine-Grained Soil
0
10
20
30
40
50
Vo
lum
etric
Wa
te
r C
on
te
nt
Minimum Maximum
0.0
0.5
1.0
1.5
2.0
2.5
MR/M
Ro
pt
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WNF Sections, Coarse-Grained Soil
0
10
20
30
40
50
Vo
lum
etric
Wa
te
r C
on
te
nt
Minimum Maximum
0.0
0.5
1.0
1.5
2.0
MR/M
Ro
pt
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DNF Sections, Coarse-Grained Soil
0
10
20
30
Vo
lum
etric
Wa
te
r C
on
te
nt
Min. Max.
0.0
0.5
1.0
1.5
2.0
2.5
MR/M
Ro
pt
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Summary
• TDR volumetric water content data from the LTPP database DataPave (Release 19) were analyzed in order to investigate volumetric water content variations in subgrade soils.
• Variations in resilient moduli were computed as a function of degree of saturation using soils data in DataPave and an empirical equation from the Mechanistic-Empirical Pavement Design Guide (M-EPDG).
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Conclusions
• Seasonal variations of volumetric water content were observed in some of the sections, with some sections having insufficient data.
• The variations between the maximum and minimum volumetric water content are typically 3% or higher and can be as high as 9% so it is concluded that moisture variations do occur in subgrade soils.
• Using moisture content variations, resilient moduli of subgrade soils vary by as much as a factor of 2 but the variations are typically lower.