Full-Scale Accelerated Testing of Multi-axial Geogrid ......(Pavement Analysis and Design, Yang H. Huang) Wheel Loading (plan view) Stresses from wheel loading produce lateral movement

Research Organization

US Army Corps of Engineers

Engineer Research and Development Center

Sections Tested/Compared

4 inches (102 mm) HMA over 8 inches (203 mm) base (control)

3 inches (76 mm) HMA over 6 inches (152 mm) base over TX5

3 inches (76 mm) HMA over 6 inches (152 mm) base over TX8

Testing Conducted

Thickness Validation & Material Characterization

Instrumentation of sections

Pavement Characterization (post construction)

HVS-A Traffic testing, FWD analysis (811,200 ESALs)

Post trafficking forensics (in-field CBR, rutting of layers,…)

Key Findings

After 800,000+ ESALs, thinner TriAx stabilized sections, over stiff subgrade soils, had less than half as much rutting as the control.

Structural benefits of TriAx exceeded SP4Pro design values.

Estimates show TriAx provides ~16% savings in construction costs, ~19-25% improvement in performance (>60% improvement in this testing) and a savings in time of ~5.5 days per lane mile.

Full-Scale Accelerated Testing of Multi-axial Geogrid Stabilized Flexible Pavements Constructed over Very Stiff Soils

Control Section Tensar TriAx TX8 Geogrid

811,200 ESALs74,583 dump trucks132,920 buses689,520,000 cars


US Army Corps of EngineersEngineer Research and Development CenterHanger 2


• Provide performance data of paved sections comparing Tensar TriAx geogrids to conventional methods over very stiff soils.

• Compare a thicker asphalt pavement to thinner stabilized asphalt pavement with a TriAx stabilized base.

• Record pavement response data in order to verify Tensar’s mechanistic models currently available on the market.

• Verify SpectraPave4Pro design values.

Objectives of Testing


Scope

• Construction, instrumentation and trafficking of test sections with TriAx stabilized bases and compare them to a control section.

• Testing to be conducted using highly controlled and monitored Accelerated Pavement Testing (APT) to gather response data, limit the risk of variability and ensure proper comparisons.


Tensar TriAx TX5 GeogridControl Section(Unstabilized)

Tensar TriAx TX8 Geogrid

TriAx Products


Standard Aperture

(Opening) Size

Smaller Aperture Size Designed for D50<= 22mm

Tensar TriAx TX5 Geogrid Tensar TriAx TX8 Geogrid

• Test sections were 10’ wide by 50’ long.

• Sections were developed following guidelines outlined by NCHRP Report 512 – with high Quality Assurance and Quality Control for subgrade prep, base placement, instrumentation, climatic monitoring.

Test Section Development

• To monitor TriAx benefits over more competent subgrade soils, this testing utilized moderate subgrade soils with a CBR of 6%.



http://www.tensarcorp.com/Tensar-Videos/accelerated-pavement-testing


• 20,000 nominal load gear weight – verified with portable scales.

• Tire pressures of 120 psi maintained throughout trafficking

Loading


Monitoring

• Instrumentation installed included earth pressure cells, Single depth deflectometers, asphalt strain gauges, pore water pressure sensors, temperature sensors, and moisture sensors.

• Pavement characterization was monitored though nuclear gauge testing, DCP testing and FWD testing.

• Instrumentation results, surface deformation, and FWD monitoring at specific intervals.

Heavy Vehicle Simulator (HVS-A). Capable of

applying loads between 10,000 and 100,000 lbs.

Uniformly distributed traffic load with typical

wander introduced.


Control

0

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Control


Total Deformation/Rutting

TX5

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Control TX5


Control


TX8

TX5

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Control

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TX8


Control


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Control

TX5

TX8

TX8

TX5

EFWD

EFWD

EFWD


Control

Total Deformation/Rutting Related to FWD Surface Modulus

0

10

20

30

40

50

EFW

D(ksi)

TX8

TX5

EFWD

EFWD

EFWD0

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Control

TX5

TX8


Control

Total Deformation/Rutting Related to FWD Surface Modulus

TX8

TX5

As the wheel passes

DefSG

DefSG

DefSG

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Control

TX5

TX8


Control

Total Deformation/Rutting Related to Subgrade Deflection

0

0.02

0.04

0.06

DEF

SG

(in

)

DefSG

As the wheel passes0

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Control

TX5

TX8


Control


TX8

TX5DefSG

DefSG

0

0.02

0.04

0.06

DEF

SG

(in

)

TX8

TX5

DefSG

As the wheel passes

DefSG

DefSG


Control

“Measured deflections in the stabilized items were approximately ½ of that observed in the unstabilized section. This may be indicative of base stiffening due to aggregate interlock at the geogrid/aggregate interface.”

Corps 2017


TX8

TX5

pSG

pSG

pSG


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Control

TX5

TX8


Control

Total Deformation/Rutting Related to Pressure on the Subgrade

0

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pS

G(p

si)

TX8

TX5


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Control

TX5

TX8


Control

Total Deformation/Rutting Related to Pressure on the Subgrade

pSG

pSG

pSG

0

10

20

30

40

pB

AS

E(p

si)

TX8

TX5

pBASE

pBASE

pBASE

Tyre pressure 120 psi0

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Control

TX5

TX8


Control

Total Deformation/Rutting Related to Pressure on the Base

TX8

TX5

AC

AC

AC


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Control

TX5

TX8


Control

Total Deformation/Rutting Related to Tensile Strain in the Asphalt

0

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AC

()

TX8

TX5

AC

AC

AC


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Control

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TX8


Control


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AC

()

TX8

TX5

AC

AC

AC

Predicted AC

for TX8 & TX5


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Control

TX5

TX8

Control




Total Deformation/Rutting Surface deformation and upheaval at edge of trafficking pattern

Surface deformation Changes in surface elevation along the centerline

Difference between total deformation and surface deformation represents the heave due to lateral spread of pavement materials.

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Control - rut


Control

Total Deformation/Rutting Related to Surface Deformation

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Control - rut

Control - def


Control


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Control - rut

Control - def

0.0

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Heave


Control


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Control - rut

Control - def

TX8 - rut

TX8 - def

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Heave

TX8


Control


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Control - rut

Control - def

TX5 - rut

TX5 - def

0.0

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Heave

TX5


Control


No significant deformation was observed in the subgrade. Accumulated deformation was found in the asphalt and base layers.


TX5 TX8

Control

Orange markers delineate boundaries between asphalt, base and subgrade.

3”

6”3”

6”

4”

8”

“Major Findings from AASHO testing…”

“… About 91% of the rutting occurred in the pavement itself: 32% in the surface, 14% in the base, and 45% in the subbase. Thus, only 9% of the surface rut could be accounted for by rutting of the embankment [subgrade]. Data also showed that changes in thickness of the component layers were caused not by the increase in density, but primarily by lateral movements of the materials.” (Pavement Analysis and Design, Yang H. Huang)

Wheel Loading (plan view)

Stresses from wheel loading produce lateral movement in the pavement materials, allowing for

deformation.


Why does the rutting/ deformation

occur?

Direction of Wheel Travel


Differences in junctionefficiency, aperture size, all impact ability to confine…

(Giroud, 2009)

Geogrid stabilizes aggregate by allowing rock particles to strike

through the openings in the geogrid (apertures). When a

load is applied to an aggregate that is held in place by a

geogrid, less movement occurs.

Interlock

“Visual investigation revealed indentions were present in the subgrade of both test items, indicating aggregate strike-through and inter-lock with the geogrid. Visual inspection indicated the geogrid was intact and no damage was sustained during construction or trafficking.”

Corps 2017


Tensar TriAx TX8 GeogridControl Section

0.50 inches 0.28 inches


TX8Stabilized Pavement500,000 ESALs

45,971 dump trucks81,928 buses425,000,000 cars

Reduction of AC by 1 inch

Decrease in deformation by >44%

Reduction of base by 2 inches

Traffic increase of >62%


~16% in cost savings

Time Savings of ~ 5.5 days per lane mile


TX5Stabilized Pavement

Tensar TriAx TX5 GeogridControl Section

0.50 inches 0.31 inches



Reduction of AC by 1 inch

Decrease in deformation by >38%

Reduction of base by 2 inches

Traffic increase of >62%

~16% in cost savings

Time Savings of ~ 5.5 days per lane mile

Cost/Value (SP4 Modeling)


Asphalt $65/ton

Base $18/cy

Excavation $5/cy

$23.31 per sy

Cost

to C

onstr

uct

495 per lm

Dum

p t

rucks

Life

224,000 ESALs

$19.48 per sy

Cost

to C

onstr

uct

371 per lm

Dum

p t

rucks

Life

266,000 ESALs

$19.63 per sy

Cost

to C

onstr

uct

371 per lm

Dum

p t

rucks

Life

281,000 ESALs

16.4% Reduction

25% Reduction

19% Increase

15.8% Reduction

25% Reduction

25% Increase

Tensar TriAx TX5 GeogridControl Section Tensar TriAx TX8 Geogrid

Tim

e S

avin

gs

5.5 days/lm

Tim

e S

avin

gs

5.5 days/lm

Summary of Testing

• TriAx stabilized sections, constructed with 25% less asphalt and base rock, allowed for significantly greater traffic and less deformation than a thicker control section.

• TriAx stabilized sections apply to pavements constructed over competent subgrades, not only in areas of soft soils.

• Estimates show TriAx provides ~16% savings in construction costs, ~19-25% improvement in performance and a savings in time of ~5.5 days per lane mile.

“…incorporation of a multi-axial geogrid in a flexible pavement base course provides a significant structural benefit.”

-- Corps 2017


Documents

Full-Scale Accelerated Testing of Multi-axial Geogrid ......(Pavement Analysis and Design, Yang H. Huang) Wheel Loading (plan view) Stresses from wheel loading produce lateral movement