field validation of geogrid mechanically stabilized layers ... · ev1 and ev2 strain modulus...
TRANSCRIPT
Field Validation of Geogrid Mechanically Stabilized Layers to Improve Pavement Performance
Joe Heintz, [email protected]
OTEC 2018October 3, 2018Columbus, OH
Fixing America’s Surface Transportation Act (2015)
Geogrid Performance MechanismsLateral Restraint & Improved Bearing
USACOE, Tingle & Webster (2003)
AASHTO R50-09
• Benefit of including geosynthetics in pavement is recognized to:• Improve life• Reduce thickness
• Benefits cannot be derived theoretically
• Designs not easily translated to other geosynthetics
• Test sections are necessary to obtain benefit quantification
• Users are encouraged to affirm their designs with field verification
AASHTO R50-09
• Benefit of including geosynthetics in pavement is recognized to:• Improve life• Reduce thickness
• Benefits cannot be derived theoretically
• Designs not easily translated to other geosynthetics
• Test sections are necessary to obtain benefit quantification
• Users are encouraged to affirm their designs with field verification
SN = 3.080 SN = 3.990 SN = 3.088 SN = 3.446
Pavement SectionCost / Benefit Analysis
7”
$28.12 / SY $31.89 / SY $24.44 / SY $27.64 / SY
AASHTO R50-09
• Benefit of including geosynthetics in pavement is recognized to:• Improve life• Reduce thickness
• Benefits cannot be derived theoretically
• Designs not easily translated to other geosynthetics
• Test sections are necessary to obtain benefit quantification
• Users are encouraged to affirm their designs with field verification
Research OrganizationUS Army Corps of EngineersEngineer Research and Development Center
Sections Tested/Compared4 inches (102 mm) HMA over 8 inches (203 mm) base (control)3 inches (76 mm) HMA over 6 inches (152 mm) base over TX53 inches (76 mm) HMA over 6 inches (152 mm) base over TX8
Testing ConductedThickness Validation & Material CharacterizationInstrumentation of sectionsPavement Characterization (post construction)HVS-A Traffic testing, FWD analysis (811,200 ESALs)Post trafficking forensics (in-field CBR, rutting of layers,…)
Key FindingsAfter 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
Control Section Tensar TriAx TX8 Geogrid
811,200 ESALs74,583 dump trucks132,920 buses689,520,000 cars
500,000 ESALs45,971 dump trucks81,928 buses425,000,000 cars
Testing StandardsNCHRP Report 512
• Accelerated Pavement Testing (APT) following NCHRP guidelines allows for isolating the performance of a geosynthetic
• APT should follow strict QA/QC standards and documentation so that the results can be analyzed and repeated
AASHTO R50-09
• Benefit of including geosynthetics in pavement is recognized to:• Improve life• Reduce thickness
• Benefits cannot be derived theoretically
• Designs not easily translated to other geosynthetics
• Test sections are necessary to obtain benefit quantification
• Users are encouraged to affirm their designs with field verification
Field ValidationCyclic Plate Load Testing
Benefits:
In situ stiffness modulus (k) values In situ resilient modulus and
permanent deformation response (Mr) values
Automation reduces testing time Simulate exact service loading
conditions to validate pavement foundation design values
Key Observations:
Resilient modulus is not constant until 100 to 1000 cycles have been achieved.
Resilient modulus is sensitive applied stress conditions - In-situ resilient modulus testing should be linked to the in-service stress conditions.
Reliability is increased when at least 5 to 7 similar tests are performed on a given test section.
10,000 cycle APLT can be used for deformation performance predictions.
Field ValidationCyclic Plate Load Testing
Research OrganizationIngios Geotechics, Inc.
Section Tested6-inches of base over TX5
Testing ConductedMr of the mechanically stabilized base courseMr of the subgradeMr composite modulusModulus of subgrade reaction (k)ev1 and ev2 strain modulus testingResilient deflections (scaling exponent)
Field Performance ValidationHunt Highway, Arizona
0.12
0.22
0.31
UnstabilizedValue
SP4 MSL DesignValue
Verified MSLValue
Laye
r C
oeff
icie
nt
Tensar TX5 Geogrid APLT Field Validation
$118,000 in savings
113% life extension
Mr (Ave) base 155,694 psi
Mr (Ave) subgrade 16,144 psi
Mr (Ave) composite 34,251 psi
Ev2 (top of stabilized base)
15.23 ksi
Ev2/Ev1 Ratio 1.60
K-value (stabilized) 392 pci
Research OrganizationIngios Geotechics, Inc.
Section Tested6-inches of Base Rock over Cement Stabilized Subgrade (CSS) (Control)6-inches of Base Rock over TX5 over CSS6-inches of Base Rock over TX130S over CSS* All sections were capped with a chip seal
Testing ConductedMr of the mechanically stabilized Base RockMr of the control section Base RockMr of the subgradeMr composite modulusResilient deflections (scaling exponent)
Automated Plate Load Testing SummaryCabeza Road, Dewitt County, Texas
Key Findings2014 APLT testing found no structural benefit in the TriAx sections immediately after construction.
2015 APLT testing, after a year of heavytraffic and precipitation, TriAx sections were found to be significantly outperforming the control section.
Research OrganizationIngios Geotechics, Inc.
Section Tested7.9–inches (200 mm)of base (control)7.9-inches (200 mm) of base over TX515.8-inches (400 mm) of base over TX5
Testing ConductedMr of the mechanically stabilized base courseMr of the subgradeMr composite modulusPermanent deformation @ 1,000 cycles
Automated Plate Load Testing SummaryHighway 63, Alberta, Canada
In-situ testing of 10 locations
Average Mr for 7.9” (200 mm) TX5 stabilized base from 950-1000 cycles
495,474 psi(a2 = 0.44)
Average Mr for 15.9” (400 mm) TX5 stabilized base from 950-1000 cycles
143,033 psi(a2 = 0.30)
Average subgrade Mr forthe TX5 stabilized sections 47,385 psi
0.0767in
0.0409 in
Control (CP_4) overSubgrade Mr 91,330 psi
TX5 (TX5_8) overSubgrade Mr 39,700 psi
Permanent Deformation of Aggregate Base @ 1000 cycles
Research OrganizationIngios Geotechics, Inc.
Automated Plate Load Testing SummaryHighway 104, Antigonish, NS, Canada
In-situ testing at 3 locations
Design Mr for TX7 stabilized base 12,330 psi (85 MPa)
Mr for TX7 stabilized base from 1000-1100 cycles
19,579 – 32,577 psi (135-225 MPa)
Mr of the subgrade 8,807 – 22,252 psi (60-116 MPa)
200 mm Agg.
480mm Agg.
Testing ConductedMr of the mechanically stabilized base courseMr of the subgradeMr composite modulusPermanent deformation @ 10,000 cycles
Intent of testing: Verify that the TX7 geogrid stabilized aggregate layer met the design value of 12,330psi (85MPa)
Section Tested19 inches (480 mm) thick aggregate base over layer of TX7 underlain by 8 inches (200 mm) aggregate base over clay
Provides full review of testing, methodology and validation of performance values
Discusses relevant mechanisms of stabilization
Confirms compliance with AASHTO R50-09 for the specific geogrids reviewed
Compliance with AASHTO R50-09Expert Review
