Ejaz,
Overloading, and subsequently the detrimental effects that has on pavement life, is a common problem in many developing countries. From experience in many African countries, excessive overloading is a reality one has to take cognizance of. Yes, the ultimate solution is effective law enforcement, but again, from my experience, not always a practical solution. As you know, high tire pressures induce substantial surface stresses in AC surface layers, and based on the information given in your example, an axle load of 30 tons, as opposed to the standard 8.2 tons, will effectively result in 179.15 ESAL loads. With simple linear elastic based pavement modeling software, the combined effect (in terms of equivalent single axle loads) can be quantified. So yes, while one can to some extent "design" for these conditions, the effect on costs to build roads to withstand these conditions will also be astronomical.
Factors to take into account to model higher loads and tire pressures , will need to include:
- Axle load and axle configuration (single, dual, tandem, etc.)
- Wheel configuration (single wheel, dual wheels, super singles, etc.) as well as spacing
- Tire pressures
This should then allow you to calculate the "design load equivalency factor" to in turn, calculate design traffic.
PS. I used ELSYM 5, or CHEV 15 in the past for calculating load equivalency factors, but there are many similar software programs available on the market that can be used.
Regards
Gerhard du Toit, PE (TX), Pr-Eng (SA), M.ASCE
Pavement Engineering Group Manager, Transportation, Northeast, USA
Gerhard.DuToit@... ------------------------------
Gerhard du Toit, PE (TX), Pr-Eng (SA)
Pavement Engineering Group Manager, Transportation, Northeast
D +1-978-905-2496
M +1-512-915-2332
Gerhard.DuToit@...AECOM
250 Apollo Drive
Chelmsford, MA, USA
T +1-978-905-2100
aecom.com
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Original Message:
Sent: 01-05-2019 10:54
From: Ejaz Khan
Subject: Designing Sustainable Pavement
In Pakistan, we are suffering from axle overloading of commercial vehicles which are the main cause of premature failure of highway pavements. The usual axle loadings experienced on highways are up to 30 tons against the standard axle loading of 8.2 tons also termed as ESAL in pavement design terminology. The tire pressure is up to 150 PSI.
Can some expert guide me what factors should be to be taken into account while designing a sustainable pavement structure for the above mentioned loading and tire pressure conditions?
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Ejaz Khan S.M.ASCE
Director
Pakhtunkhawa Highways Authority
Islamabad
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