Laval Universitys experience with the widebase single tires
Laval University’s experience with the wide-base single tires Guy Doré
Project background • Trucking industry pushing for unrestricted use of WBST • Highway administrations concerned about possible damage to pavement networks • Decision to conduct experimental work to try to quantify impact of WBST on pavement performance
Project partners • • Quebec ministry of transportation (MTQ) Transport Robert Michelin Canada Laval University
Project outline • State of the art • Field testing – Spring time – Summer time
Test site • Laval University Road Experimental Site (SERUL) • Test section of vehicle-pavement interaction • « Typical » pavement structure: – 100 mm HMAC – 200 mm DGAB – 450 mm GSB – Relatively stiff subgrade soil (silty till)
The heavy vehicle – pavement interaction section at the SERUL
Pavement instrumentation • Pavement condition – Temperature sensors – Moisture sensors • Pavement response – Vertical strain in pavement layers (MDD - ez) – Horizontal strains at base of bound layer (eh) – X-Y-Z strains at shallow depth in bound layer (es)
Epoxy/aggregates plate Strain gauges Multi-level deflectometre 7, 60 m 100 mm Travel direction # 4 #5 0, 30 m #6 #7 Strain gauges 0, 30 m Instrumentation layout # 3 300 mm 800 mm # 2 1100 mm # 1 2500 mm
Multi-depth deflectometer
Fibre optic horizontal strain sensors
Test plate including an array of 60 strain sensors at shallow depth in epoxy concrete L 45 TR 30 V 4 V 21 V 20 V 19 V 18 V 3 V 2 V 1 T 1 L 44 L 43 TR 36 TR 35 V 17 V 16 V 15 TR 34 L 42 L 41 TR 33 TR 32 TR 31 V 14 V 13 V 12 V 11 V 10 V 9 V 8 V 7 T 2 T 3 T 4 V 6 L 40 V 5
Testing protocol • General: – Semi-trailer with tandem axle – Tests done under a moving load (50 km/h) for er and ez • One test = average of 5 valid passes (within 50 mm of target) – Test done under static loading for es – All tests conducted relative to a standard load (BB truck)
Testing protocol • Specific factors – Type of tyre • Dual 11 R 22, 5 & 12 R 22, 5 • Single 385 & 455 – 5 levels of loading • 3000 – 7000 kg – 3 levels of tyre pressure • 560 – 730 – 900 k. Pa
Test vehicles
Typical results Characteristics of tire contact area Vertical displacements of pavement interfaces – Vertical strains in pavement layers
Typical results Horizontal strains at the base of the HMAC layer Vertical and shear strains at shallow depth in test plate
Results highlights: Vertical strains on SS (structural rutting) • For same load level: no significant effect of tyre type or tire pressure (as expected)
Results highlights Horizontal strains (spring) at the base of the HMAC layer (Fatigue cracking) Longitudinal Transversal WBST 25% - 65% more damaging during spring time
Results highlights: Horizontal strains (summer) at the base of the HMAC layer (Fatigue cracking) Longitudinal Transversal WBST from 55% less to 50% more damaging during summer time
Results highlights Horizontal strains at the base of the HMAC layer (Fatigue cracking) • Horizontal strains at base of bound layer (Fatigue cracking) – WBST more damaging than dual tyres during spring thaw – WBST slightly more damaging than dual tyres during summer
Results highlights: Strains at shallow depth in bound material (stability rutting – TD cracking) 11 R 22, 5 455 33% reduction in vertical strains 30% reduction in shear strains
Results highlights • Strains at shallow depth in bound layer (stability rutting – TD cracking) – WBST less damaging than dual tyres
Conclusion • Systematic investigation on the effect of WBST on pavements based on experimental results • Tests valid for mid-class roads for results based on ev and eh • Test valid for mid to high class roads for results based on es
Conclusion • Experimental results suggest: – Based on structural rutting criteria: no significant difference between WBST and dual tires – Based on a fatigue cracking criteria: WBST appear to cause more damage than dual tires and more specifically during spring time – Based on stability rutting criteria: WBST appear to cause less damage than dual tires
Future research activities • CTI • Effects of WBST on low volume roads – Thin HMAC – Surface treatment • i 3 C industrial research chair
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