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
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.
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.
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
Seasonal Monitoring Program (SMP)
63 Sites with Seasonal Instrumentation
Four Climatic Regions
SMP Instrumentation
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
(%
)
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 (%
)
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
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)
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
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
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
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
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
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
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
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
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).
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.