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.