Workshop on the Mechanistic Design & Evaluation of Unsealed & …€¦ · & Evaluation of Unsealed...

US Army Corpsof Engineers ERDC-Cold Regions Research and Engineering Laboratory

Workshop on the Mechanistic Design & Evaluation of Unsealed & Chip-

Sealed Pavements

University of Canterbury WorkshopNovember 2002


Base Course Deformation & Subgrade Failure Criterion

Dr. Vincent JanooUS Army COEERDC/CRREL

Hanover, NH, USA 03755


Mechanistic Design/Process Process

Stress, StrainDisplacement

Failure Criteria

PerformanceCriteria

MET ?

Pavement Structure

ClimaticEffects

Material Properties

(Elastic,Plastic, Viscous)

Load History

Analytical ToolsMulti-layered,

FEM

EndYesNo


FACTORS AFFECTING FAILURE OF SUB-SURFACE LAYER

• EXCESSIVE LOADING

• SEASONAL FACTORS– Change in material

properties (f (ω))– Drainage


Failure Criteria• Failure Criteria

– Subgrade rutting –limiting the strain on top of the subgrade.

– Asphalt fatigue cracking – limiting the tensile strain (εh) at bottom of AC layer.

AC

Base

Subgrade


Failure Criteria

• Not aware of base course failure criterion


Subgrade Failure Criteria

• Ottawa, Illinois, USA• 1956 to 1960• A – 6 (ML) subgrade• Test speed – 56

km/hr• Channelized traffic• 1,114,000 axle loads

applied over ~ 2 year period.


Subgrade Failure Criteria• PRIMARY

– Provided data for current AASHTO thickness design.

– Basis of design – limit loss of serviceability over design life

• SECONDARY– Failure criteria for

mechanistic pavement design(Shell, Asphalt Institute)


Subgrade Failure Criteria• Subgrade failure

criterion– Based on one soil,

one location– Most failure occurred

in subbase– Most failure occurred

during the spring thaw

– Subbase material properties estimated from CBR


Current Research

Improved Subgrade Failure Criteria for Mechanistic Design

Funded by – Federal Highway Administration – State Department of Transportation

• Pooled Fund Study (17 States)


Frost Effects Research Facility

• 2,700 m2 environmentally controlled building. • Facility is 56 m long by 31 m wide.• 12 test cells, 6.4 m wide.

– 8 cells are 7.6 m long and 2.4 m deep.– 4 cells are 11.3 m long and 3.7 m deep.

• Cells can be made impermeable to simulate the raising and lowering of the water table.

• Ambient air temperature within the facility can be controlled from -4 °C to 24 °C with a ± 2 °C tolerance.

• The temperature can be further reduced or increased using surface panels (- 32 °C to 49 °C).


FERFFERF• Accelerated testing

– Load (HVS)– Climate

• Controlled environments– Temperatures: -37 to 49 °C– Water table– Freeze/thaw (6 cycles/year)

• Full-scale pavement sections– Surface course – Base and subgrade

• Test basins– Flexible, to 30 x 15 x 4 m

• Instrumentation– Temperature– Moisture– Stress– Strain– Profilometer


Construction


75 mm AC75 mm AC

229 mm Base

3 m Subgrade3 m Subgrade


0

10

20

30

40

50

60

70

80

90

100

0.00010.0010.010.1110100

Grain Size (mm)Grain Size (mm)

Perc

ent F

iner

Perc

ent F

iner

A-2-4A-4A-6A-7-6


Heavy Vehicle Simulator

Wheel Load …………………20 – 100 kN roadwayUp to 200 kN airfield

Test Wheel ………………….Single, Dual or AircraftTire Pressure ……………….550 – 757 kPa on roads;

up to 1450 kPa on airfieldsRepetitions,Per Hour …….600 (uni-directional)Trafficked Length ………….Approximately 7 mTrafficked Width ……………Variable up to 1.5 mTrafficked Pattern ………….VariablePower ………………………..Electric


LASER PROFILOMETER FOR SURFACE RUT MEASUREMENTS


InstrumentationInstrumentationInstrumentationStress CellsStress Cells

Coil Gages Coil Gages (Strain)(Strain)

9” (229 mm) diameter,200 psi (1379 kPa)

4” (102 mm) diameter


0.0001

0.001

0.01

0.1

10 100 1000 10000 100000 1000000 10000000

Load Repetition

Failu

re S

trai

n (m

m/m

m)

Asphalt InstituteShell (50% Reliability)A-4 (optimum)A-4 (wet)A-2-4 (optimum)A-2-4 (wet)A-6 (wet)


Base Course Failure


0

20

40

60

80

100

0.010.1110100Diameter (mm)

Perc

ent f

iner

by

wei

ght

GP-GM

Fines were Non-PlasticModified Proctor

γd = 2162 kg/m3

ω = 6 %


AC

BASE

SUBGRADE

76 mm

229 mm

152 mm

LOCATION OF εMU (STRAIN) GAGES

114 mm115 mm


TYPICAL STRESS MEASUREMENTS IN BASE COURSE

0

50

100

150

200

250

0 1 2 3 4Time (seconds)

Load = 63 kN

Tire Pressure = 746 kPa

0

10

20

30

40

50

60

70

0 1 2 3 4

Time (seconds)

-4000-3500-3000-2500-2000-1500-1000-500

0500

1000

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Time (sec)

ACBASE

SUBGRADE

TYPICAL STRAIN MEASUREMENT IN BASE COURSE

Load = 63 kNTire Pressure = 746 kPa

TEST DATA

3.0189521.0164216A-6 (CL)706

198823.016658A-4 (CL)705

3.0216919.917008A-4 (CL)704

3.7213715.418532A-2-4 (SM)703

2.4207115.520718A-4 (CL)702

3.020689.019002A-2-4 (SM)701

ω (%)γ(kg/m3)

ω (%)γ(kg/m3)

BaseSubgradePISubgradeTest

Section

0

10

20

30

40

50

60

70

80

90

100

0 20000 40000 60000 80000 100000 120000

Load Repetition

Stre

ss (k

Pa)

Transverse

Vertical


0500

100015002000250030003500400045005000

0 50000 100000 150000 200000 250000 300000

Load Repetitions

103 kN, 758 kPa

89 kN, 748 kPa

80 kN, 690 kPa

SM subgrade

P k t i i b

0

2000

4000

6000

8000

10000

12000

14000

0 200000 400000 600000 800000 1000000 1200000Load Repetitions

Peak

Ver

tical

Str

ain

(mst

rain

) 81 kN, 707 kPa

CL subgrade

71 kN, 705 kPa63 kN, 746 kPa

61 kN, 787 kPa 54 kN, 737 kPa

0

100

200

300

400

500

600

0 10000 20000 30000 40000 50000 60000

Load Repetitions

Vert

ical

str

ain

( µst

rain

)


Top

Bottom

Bottom strains ~ 30-50% of Top

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0 50000 100000 150000 200000 250000 300000

Load Repetitions

Per

man

ent D

efor

mat

ion

(mm

)

80 kN, 690 kPa89 kN, 748 kPa

SM subgrade

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0 50000 100000 150000 200000Load Repetitions

Per

man

ent D

efor

mat

ion

(mm

)

67 kN, 716 kPa81 kN, 707 kPa63 kN, 746 kPa61 kN, 787 kPa71 kN, 705 kPa

CL subgrade

5

10

15

20

25

30

35

40

45

50

Subg

rade

Pre

ssur

e (k

Pa)

FER

F E

xper

imen

t

AA

SH

TO R

oad

Test

Typi

cal S

tate

Hig

hway

Spe

ed

Case Ratio Stress Reduction Factor

FERF to AASHTO Road (26/41) 0.63 FERF to State Highway (19.5/41) 0.48

1

10

100

1000

10000

100,000 1,000,000 10,000,000ESAL

Vert

ical

Str

ain

( µst

rain

) CL subgrade

SM subgrade

Rut Depth = 25 mmSpeed = 100 km/hour

y = 256583 x –0.363

y = 8148 x –0.236

– We have developed a new subgrade failure criterion as a function of subgrade type.

– Deformation of the base course is a function of the subgrade type.

– Higher percentage of rutting is in the base course

– Preliminary failure criterion for base course as a function of subgrade type is presented.

Conclusions

ANY QUESTIONS????

Workshop on the Mechanistic Design & Evaluation of Unsealed & …€¦ · & Evaluation of Unsealed...

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Transcript of Workshop on the Mechanistic Design & Evaluation of Unsealed & …€¦ · & Evaluation of Unsealed...