Pavement Construction QA · Pavement Construction QA ... (deflections, moduli, stresses and...

Pavement Construction QAPredicting Finished Surface Parameters (deflections,

moduli, stresses and strains) from in situ testing duringconstruction at subgrade and/or subbase level

FSP ProjectComparisons and calibration of a pavement model that will correctly

predict performance in materials that have non-linearcharacteristics. (Stress-dependent properties).

Regional and site specific calibration

Programme - completed to Stage 5

Stage 1. FWD Tests on SIL (subgrade improvement layer) preferably subgrade alsoStage 2. Establish alternative models to predict performance of the pavement aftereach overlying layer is place. (Stresses, strains, moduli and deflections.)Stage 3. Tests on subbase to refine predictionsStage 4. Tests on basecourse to verify predictions for the “green” condition.Stage 5. Develop a simple spreadsheet to predict (1) properties after each layer isplaced (green), and (2) after bedding in from trafficking, and (3) hence predictexpected life.Stage 6. Tests after 20,000 ESA to establish bedding in.Stage 7. Refinement then validation of spreadsheet modelsStage 8. Reporting

Candidate pavements for study

• Minimal response with suitable case histories.• One site from NZTA, but no funding available, and a very lengthy task.• NZTA prefer empirical deflection based approach• However mechanistic approach will encompass a wider field of variables.

More insight provided by layer moduli, stresses/strains• Both empirical and mechanistic have been accommodated, and 3 models

used so far• Lengthy process to develop a universal model, but making progress

• Would appreciate more case histories, but must be from someone who hasdetailed knowledge of what happened during construction.

FWD testing on top of SIL layerAll runs have been modelled with SIL on infinite subgrade. Non-linearity of subgrade modulus calculated usingtraditional method (ELMOD). This package models only subgrades that are stress softening. ELMOD indicates thissubgrade varies from linear elastic to slightly stress softening. No FWD indication of any stress hardening.Conflicts with RLT, or is this just the criterion used, ELMOD equation for stress softening is Es= C0 (sv/100 kPa)^n

Method : Austroads deflection (linearelastic similar)

ELMOD ELMOD plus regional calibration.

ModulusDependence

Constant Deviator Stress Deviator Stress plus Confinement

Comments Inclusion of psuedo rigidlayer at depth, cangenerate any lesserdeflection that is desiredbut vertical strain at top ofsubgrade will be wrong.

Traditional method, goodwhen the totalincrement in pavementthickness is minimal, sayless than 100 mm.Otherwise result variessignificantly from reality.

Uses regional database ofstructural analyses to provide areality check adjustment forconfinement, after ELMOD’sdeviator stress model has beenapplied.

Non-linear Moduli

First site tested: Subgrade non-linearity at the site studied ranges from 0 to -0.35but most tests are around -0.1 to -0.2 and that is only slight non-linearity. (Fromcomparisons with national LTPP sites, less than -0.6 is strongly non linear)

Note: Two thirds of NZ pavements have non-linear subgrades (much greaterthan in Australia). A solution is essential for meaningful predictions.

Using the ELMOD solution for stress dependent moduli, (subgrade modulusdependent on deviator stress) the worst test point would need additional goodquality granular layers totalling 390 mm.

Using the ELMOD solution with stress dependent moduli, then correcting thatusing subgrade characteristic improvement for confinement, the requirementfor good quality granular layer totals 320 mm

Precedent Performance Design Spreadsheet

Spreadsheet now adapted to automate the iterative procedure for calculating non-linear moduli and strains

(Increasing the subgrade modulus results in increases in moduli of overlying granular layers, which in turn providesbetter loadspread ie less stress at top of subgrade and hence greater subgrade modulus. The process is then iteratedand essentially converges after 3 or 4 iterations.

Precedent Performance Design Spreadsheet Input cells in yellowfrom FWD testELMOD output (Es,nes, LDE, kn, kc)

Input cellsSubgrade modulus at 100 kPa referencestressELMOD non-linearity exponentStrain at top of subgrade at FWD stressLoad damage exponentCalibration constants from precedentperformance.

Precedent Performance Design Spreadsheet

Cumulative damage factor for proposed design is0.47 for subgrade strain, <1 so design is OK (butbasecourse life will govern as CDF is 0.56)

Conclusion from FWD testing on top of SIL layer

Requiredsubbase plusbasecoursethickness(mm)

0

100

200

300

400

500Overlying Granular Layer Thickness (mm)

Method Austroads deflection(linear elastic similar)

ELMOD ELMOD plus regionalcalibration.

ModulusDependence

Constant Deviator Stress Deviator Stress plusConfinement

Function C f ( 1/s1) f (1/s1, s3)

End of main presentation.

• Attachments

FWD Analysis NGARUAWAHIA SIL

0102030405060708090

100

0 0.5 1 1.5 2 2.5

Perc

enta

geof

sam

ples

<X

Standard Central Deflection (mm)

All runs

NB_L1_6960_7080-Cement Stabilised SB on Brown Rock (25/08/2014) NB_L1_7820_8140-Cement Stabilised SB on Sand SIL (25/08/2014)


SB_L1_6680_6840-Subbase not stabilised on Sand SIL (25/08/2014) SB_L1_7760_8800-Brown Rock SIL (22/08/2014)


Composite Plot

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5

Curv

atur

eFu

nctio

n(m

m)


-0.5

-0.45

-0.4

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

10 100

Subg

rade

Mod

ulus

Expo

nent

Subgrade Modulus (100kPa Loading)

Non-linearity (Exponent <0)

FWD testing on top of SIL layerThe initial subgrademoduli range by anorder of magnitude.

And so does SILmodulus (includesstabilised soils).

However , modularratio between top ofSIL and top ofsubgrade is one totwo orders ofmagnitude

0

10

20

30

40

50

60

70

80

90

100

10 100

Perc

enta

geof

sam

ples

<X

Subgrade Modulus (MPa)

All runs – Cumulative Distribution of Subgrade Modulus (MPa)





Composite Plot

0

10

20

30

40

50

60

70

80

90

100

-0.44 -0.39 -0.34 -0.29 -0.24 -0.19 -0.14 -0.09 -0.04

Perc

enta

geof

sam

ples

<X

Subgrade Modulus Exponent

All runs – Cumulative Distribution of Subgrade Modulus Exponent





Composite Plot

0

10

20

30

40

50

60

70

80

90

100

100 1000

Perc

enta

geof

sam

ples

<X

Top 100 mm of SIL, Modulus (MPa)

All Runs – Modulus of top 100 mm of SIL (MPa)





Composite Plot

0102030405060708090

100

0 50 100 150 200 250 300 350 400 450 500

Perc

enta

geof

sam

ples

<X

Granular Overlay (mm) - Austroads 2011 (Part 5)

All runs- Granular Overlay (mm) - Austroads 2011 (Part 5)





Composite Plot

Austroadsdeflection basedmethod (similarto results oflinear elasticmodel?)

Up to 500 mm ofadditionalgranular layersindicated.

0102030405060708090

100

0 100 200 300 400 500

Perc

enta

geof

sam

ples

<X

Granular Overlay (mm) - Austroads (GMP-Rigorous) All Layers

All Runs Granular Overlay (mm) - Austroads (GMP-Rigorous NL) All Layers





Composite Plot

Austroads subgradestrain criterion (iso)and using ELMODstress dependenceof subgrade modulus

Up to 390 mm ofadditional granularlayers indicated.

0102030405060708090

100

0 100 200 300 400 500

Perc

enta

geof

sam

ples

<X

Granular Overlay (mm) - GMP Method, adjusted for Stress/StrainDependence

All Runs - Granular Overlay (mm) - GMP, adjusted for Stress/StrainDependence





Composite Plot

Austroads subgradestrain criterion (iso)and using ELMODstress dependenceof subgrade modulusplus calibration toconfinement ofsurcharge layers

Up to 320 mm ofadditional granularlayers indicated.

0

50

100

150

200

250

300

350

400

450

0 0.5 1 1.5 2 2.5

Gra

nula

rOve

rlay

(mm

)-A

ustr

oads

(GM

P-Ri

goro

us)A

llLa

yers

Standard Central Deflection on SIL (mm)

All Runs

0

50

100

150

200

250

300

350

0 0.5 1 1.5 2 2.5

Gra

nula

rOve

rlay

(mm

)-G

MP

Met

hod,

adju

sted

for

Stre

ss/S

trai

nDe

pend

ence


All Runs

-0.5

-0.45

-0.4

-0.35

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

0

0 0.5 1 1.5 2 2.5

Subg

rade

Mod

ulus

Expo

nent


All Runs

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300 350

Gra

nula

rOve

rlay

(mm

)-G

MP

Met

hod,

adju

sted

forS

tres

s/St

rain

Depe

nden

ce


All tests on SIL

0

100

200

300

400

500

600

7.7 7.8 7.9 8 8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8

Gra

nula

rOve

rlay

(mm

)

Chainage (km)

SB_L1_7760_8800-Brown Rock SIL (22/08/2014)


Granular Overlay (mm) - Austroads 2011 (Part 5)

Granular Overlay (mm) - GMP Method, adjusted for Stress/Strain Dependence

Big differences in overlayrequirements, usingdifferent methods.

Hence, possible solutionmay be 30 m long trialpad at weakest point,Ch 8.15 Southbound inLane 1.

Construct 180 mmsubbase and 180 mmtemporary subbase, with30 FWD tests at 1 mintervals on each layer

Pavement Construction QAPredicting Finished Surface Parameters (deflections,

moduli, stresses and strains) from in situ testing duringconstruction at subgrade and/or subbase level

FSP Project

Comparisons and calibration of a pavement model that will correctlypredict performance in materials that have non-linear

characteristics. (Stress-dependent properties).

Regional and site specific calibration

Pavement Construction QA · Pavement Construction QA ... (deflections, moduli, stresses and...

Documents

Transcript of Pavement Construction QA · Pavement Construction QA ... (deflections, moduli, stresses and...