Discussion: View Thread

Designing Sustainable Pavement

  • 1.  Designing Sustainable Pavement

    Posted 01-05-2019 10:56 AM
    Edited by Tirza Austin 01-05-2019 10:55 AM

    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? 



    ------------------------------
    Ejaz Khan S.M.ASCE
    Director
    Pakhtunkhawa Highways Authority
    Islamabad
    ------------------------------


  • 2.  RE: Designing Sustainable Pavement

    Posted 01-06-2019 10:01 PM
    Edited by Tirza Austin 01-06-2019 10:01 PM
    That question is within a broad topic of pavement design and performance.  More specific information might generate some productive responses.  When you refer to "failure," are we talking about asphalt fatigue cracking?  Asphalt oxidation?  Rutting of asphalt pavement?  Cracking of concrete pavement?  What is the sub-grade soil type?  Are you familiar with the USA AASHTO pavement design method for highways and arterial roadways?  Do you perform traffic counts in Pakistan to attempt to estimate traffic loads (truck loads and truck sizes and truck frequency)?  I know nothing about Pakistan pavement construction, maybe you can indicate to everyone here what materials you typically use and what a typical commercial traffic roadway pavement section might consist of in terms of local materials and thickness.

    ------------------------------
    Nicholas Kauffman P.E., M.ASCE
    Geotechnical Engineer
    Capital Geotechnical Services PLLC
    Austin, Texas, USA
    ------------------------------



  • 3.  RE: Designing Sustainable Pavement

    Posted 01-06-2019 10:03 PM
    Edited by Tirza Austin 01-06-2019 10:02 PM
    The first thing you need to do is to work with law enforcement to get an overweight vehicle enforcement program.  And also work with the courts to be sure that the prosecutors and judges impose substantial fines against the illegal truckers.

    In our State of Colorado, the truckers have an organization called the Colorado Motor Carriers Association.  They work to improve truck safety among their members and to protect themselves from harmful legislation at the State capitol.  The support weight enforcement programs, because it is "fly-by-night" illegal operators that drive overweight and unsafe trucks.  The good trucking companies want everyone to compete on a level playing field.  It is clear that illegal operators profit at the expense of the rest of society!

    You can't afford to build all of the pavements sufficiently thick to distribute the overweight loads without causing damage to the pavement sections.  It is in your country's interest to enforce the weight limit laws!

    ------------------------------
    Stephen Mueller P.E., M.ASCE
    President and Owner
    The Stephen Mueller Consultancy
    Littleton, Colorado, USA

    ------------------------------



  • 4.  RE: Designing Sustainable Pavement

    Posted 01-07-2019 08:03 AM
    Edited by Tirza Austin 01-07-2019 02:34 PM
    The first thing you need with any construction is a proper soil investigation; then see what materials and techniques may be locally available to improve the subgrade and keep it drained.

    ------------------------------
    Hans H. Coucheron-Aamot
    [Retired]
    Albuquerque NM
    (505) 897-2554
    ------------------------------



  • 5.  RE: Designing Sustainable Pavement

    Posted 01-09-2019 11:26 PM
    Edited by Tirza Austin 01-09-2019 11:25 PM
    The last thing any pavement engineer wants to do is outlaw all cars and trucks.

    Pavement design is based on several factors - but every factor has certain limitations. When the actual loading greatly exceeds the normal design parameters on a system-wide basis, as our colleague from Pakistan has described, there are two approaches to solve the issue:
    1) upgrade the entire roadway network to accommodate the excessive loads from a limited number of heavy vehicles. OR
    2) stop the super heavy vehicles from driving on the pubic roads.

    In the USA, we know that 2) is a more cost effective approach. When you run the numbers to upgrade the entire network, you will become a believer and support improved overweight vehicle enforcement programs. 

    As an engineer, I can design a pavement to accommodate a heavy load - but my professional ethics also demand that I offer the most cost effective method for solving my clients problem. In this case, the most cost effective method doesn’t involve an engineering solution for a system-wide issue.




  • 6.  RE: Designing Sustainable Pavement

    Posted 01-10-2019 10:03 AM
    Edited by Tirza Austin 01-10-2019 10:03 AM
    I suspect that the trucks Mr. Khan is talking about are those hauling supplies and munitions up into Afghanistan and he is in no position to enforce weight limits on those.

    What he is asking for is help in providing designs that will hold up under these trucks on those routes.

    ------------------------------
    Hans H. Coucheron-Aamot
    [Retired]
    Albuquerque NM
    (505) 897-2554
    ------------------------------



  • 7.  RE: Designing Sustainable Pavement

    Posted 01-11-2019 08:07 AM
    Edited by Tirza Austin 01-11-2019 08:07 AM
    Yes Sir, you are absolutely right if some expert guides me to design by giving emphasis on the pavement layer or strengthen the sub-grade to take the axle load up-to 30 tons instead of standard axle load of 8.2 tons and tire pressure up to 150 PSI to make my country pavement sustainable 
    I am grateful Sir for your kind interest.  
    Regards, 

    Ejaz Ahmad Khan 





  • 8.  RE: Designing Sustainable Pavement

    Posted 01-08-2019 08:05 AM
    Edited by Tirza Austin 01-08-2019 08:04 AM
    As I see that overloading is a phenomenon which happens almost everywhere. This results in failure of pavement, then reconstructing and then again failure whch goes on. But why truckers generally overload - because of more profit or because of taxes and levies imposed by Government which renders legal weight limit uneconomic or because of limit of carrying due to less trucks available in any particular area or route. 
    Overdesigned pavement is not a solution as the road will still fail over a period of time due to constant overloading.
    I throw the question open to the experts.

    ------------------------------
    Partha Aich M.ASCE
    Senior Vice President
    Delhi East ND
    9111 42402011
    ------------------------------



  • 9.  RE: Designing Sustainable Pavement

    Posted 01-08-2019 10:52 PM
    Edited by Tirza Austin 01-08-2019 10:51 PM
    I would agree with all the comments and suggestions and only have this to add, enforcement will go a long way towards leveling the playing field, however, with a shortage of enforcement staff and in many instances a lack of will-- the solution lies in technology.  I propose a utility fee on each mile traveled, the "life taken" assessment would be based on the load supported, the fees collected would be reimbursed to the construction fund and put toward the future reconstruction of the same mile. The fee would be audited and adjusted much as water, waste water and other utilities are set. Now the only hold up is political, and if the recent past is any indicator there is little political will to address the problem.

    ------------------------------
    Barry Anderson P.E., M.ASCE
    Granite Falls MN
    (320) 564-4500
    ------------------------------



  • 10.  RE: Designing Sustainable Pavement

    Posted 01-07-2019 09:44 AM
    Edited by Tirza Austin 01-07-2019 09:44 AM
    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
    ------------------------------



  • 11.  RE: Designing Sustainable Pavement

    Posted 01-08-2019 08:06 AM
    Edited by Tirza Austin 01-08-2019 08:06 AM
    I find this discussion very interesting and technically informative.
    I understand now how significant are tire pressure, axle load and overloading factors are for pavement design! Thanks Mr. Gerhard Du Toit.

    ------------------------------
    Peter Singh M.ASCE
    Managing Director
    Kingdom Designers
    Birganj
    9779855020043
    ------------------------------



  • 12.  RE: Designing Sustainable Pavement

    Posted 01-09-2019 12:16 PM
    Edited by Tirza Austin 01-09-2019 12:15 PM
    This is as much a social engineering as a civil engineering challenge. The social engineering element will be solved when the population as a whole comes to grips with the need for sustainable and affordable roadways - to which a bit of enforcement for limiting weights is the encouragement. Taxation could be a partial solution as could the prohibition of the importation or manufacturing of tires beyond certain inflation pressures. Other solutions could include truck lanes that are reinforced to handle the loads. Perhaps geotechnical conditions in certain limited areas could handle these high loads - such as areas where the sub-grade is composed of sufficiently stout material.

    Putting aside flagrant violators, subsistence living standards may be pushing these owners & drivers to load up their vehicles to these extents.

    ------------------------------
    Christian Steinbrecher P.E., M.ASCE
    President
    Ukiah Engineering, Inc.
    PORTLAND OR
    (503)292-2165
    ------------------------------



  • 13.  RE: Designing Sustainable Pavement

    Posted 01-10-2019 11:22 AM
    Edited by Tirza Austin 01-10-2019 11:22 AM
    In Pakistan, we are designing pavement structure by using AASHTO empirical method of pavement thicknesses design. First we worked out the traffic rather classified traffic then convert it to ESAL by multiplying it with the equivalency number as you all are aware that each classified vehicle has its specific equivalency no. Then we worked out commutative ESAL for 10 years. These are then the design ESALs which the pavement will be experiencing through the design life of 10 years. After this we explore the soil properties specially the sub-grade and it's classification plasticity index CBR and Modulus of resilient are worked out. Then according to the AASHTO equation by sitting the reliability serviceability and other parameter the structure no is worked out and then the respective thicknesses. The usual design are as follows:

    Soil is usually A4 with passing no 200 usually up to 85 percent and CBR is 8 to 15 percent PI is usually 8 to 10 percent.  

    Sub-base 25 CM. Waterbound macadam is 30 CM asphaltic base course is 8 cm and ACWC is 5 cm.  

    Still rutting specially pavement rutting and fatigue cracks are the usual phenomenon in the wheel track after 2 to 3 years. 

    ------------------------------
    Ejaz Khan S.M.ASCE
    Director
    Pakhtunkhawa Highways Authority
    Islamabad
    ------------------------------



  • 14.  RE: Designing Sustainable Pavement

    Posted 01-11-2019 05:28 PM
    Edited by Tirza Austin 01-11-2019 05:27 PM
    Assuming adequate subsurface drainage, perhaps the sub-grade is pumping into the base course. This could be prevented by using fabric under the base course.

    ------------------------------
    Daniel Clark P.E., M.ASCE
    Consulting Civil Engineer
    Auburn CA
    ------------------------------



  • 15.  RE: Designing Sustainable Pavement

    Posted 01-13-2019 09:35 AM
    Edited by Tirza Austin 01-13-2019 09:35 AM
    Earth Science Products Corp manufacturers Condor SS a liquid soil stabilization product that chemically treats fine soils (>30% passing #200). Eliminates pumping and improves compaction ​​​of sub-grade soil reducing amount of subbase aggregate requirements. Saves construction and maintenance costs.

    ------------------------------
    Jeffrey Jensen Aff.M.ASCE
    President
    Earth Science Products Corp
    Wilsonville OR
    ------------------------------



  • 16.  RE: Designing Sustainable Pavement

    Posted 01-13-2019 10:53 AM
    Edited by Tirza Austin 01-13-2019 10:52 AM
    How is the availability of fly ash in Pakistan?

    There should be a lot of information on the internet these days about how to stabilize sub-grade and/or base courses with fly ash.

    ------------------------------
    Hans H. Coucheron-Aamot
    [Retired]
    Albuquerque NM
    (505) 897-2554
    ------------------------------



  • 17.  RE: Designing Sustainable Pavement

    Posted 01-14-2019 03:16 PM
    Edited by Tirza Austin 01-14-2019 03:15 PM
    Here, the main issue is overloading which is about 4 times the standard load, and it would be uneconomical to increase the thickness.  I would suggest that first focus on sub-grade stabilization, a professor at NUST Islamabad has conducted tests on sub-grade stabilization using sugarcane Bagasse Ash. You may contact him in this regard. Also, I have observed that sometimes the <g class="gr_ gr_704 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling ins-del" id="704" data-gr-id="704">rutting</g> is due to weather conditions especially hot summer in Pakistan. On some sections of highways in the mountain areas (high grades), you can use rigid pavement on outer lanes for trucks (also paved on M-2 near Salt range).

    ------------------------------
    Sajid Raza, Registered Engineer
    Graduate Research Assistant
    University of Alaska Anchorage
    Anchorage, Alaska
    sraza@...
    907-223-5720
    ------------------------------



  • 18.  RE: Designing Sustainable Pavement

    Posted 01-20-2019 09:17 AM
    Edited by Tirza Austin 01-20-2019 09:17 AM
    Dear Sajid Raza, 

    You are right Sir, but It's not only the subgrade we need to work on tests protocol of various layers to sustain the overloading of axle above 8.2 tons or in Pakistan we called it legal weight per axle which is 12 tons. I am of the opinion that we should work out the stress on top of subgrade for overloaded axle and also work out the depth below subgrade to which the stress propagates for replacing the weak soil from that depth. Then we need to replace or improve the soil for taking the real or actual axle load which the subgrade will experience. Moreover we also need to check the state of compaction and strength of pavement layers like sub-base ' base and bound layers to resist the overloaded stresses that will be experiencing by the structure layers. I will give you one example. Take the case of standard and modified proctor compaction, AASHTO has switched over to modified proctor because the compaction of standard proctor was become insufficient to resist. Based on this analogy we need to move forward. 

    Thanks and regards, 

    ------------------------------
    Ejaz Khan S.M.ASCE
    Director
    Pakhtunkhawa Highways Authority
    Islamabad
    ------------------------------



  • 19.  RE: Designing Sustainable Pavement

    Posted 01-20-2019 01:32 PM
    Edited by Tirza Austin 01-20-2019 01:32 PM
    The single most important thing in asphalt pavements is the gradation. On a 0.45 power chart it should run in as straight a line as possible with a slight break at the No. 4 screen to allow room for adequate asphalt content. As for the "forbidden zone," go under, not above.

    (I have had an asphalt plant operator and a soils lab principal volubly thank me for insisting that they work with 0.45 gradation charts., both for designing mixes and daily field testing. I don't quite understand it, but they both said it was the best thing I ever did for them.)

    As for testing, my inspectors would insist on getting the initial lab results phoned back to them within the hour, or they would find another lab to do the testing. Likewise continual testing with nuclear devices for density. If there is a problem with asphalt, it needs to be fixed while the mat is still hot if at all possible.

    When calibrating densometers, take the densometer reading first, then draw around it with chalk and take the core sample in the center. 3 samples, and they will correlate remarkably well. 12 inches away, not so good. Neither asphalt nor concrete are homogeneous materials.

    ------------------------------
    Hans H. Coucheron-Aamot
    [Retired]
    Albuquerque NM
    (505) 897-2554
    ------------------------------



  • 20.  RE: Designing Sustainable Pavement

    Posted 01-20-2019 05:00 PM
    Edited by Tirza Austin 01-20-2019 05:00 PM
    Dear Ejaz Khan,
    Yes, you are right that we should not only focus on subgrade. If you want to analyze the stresses and depth of stress in subgrade, you may use any pavement design/analysis software and work this out. Then you can proceed to the next steps. But another suggestion is that the construction of pavement is also one of the main components. In Pakistan, some contractors may not be following the mix design protocols very strictly, i.e. asphalt content, and mixing and paving temperature etc. so also you should think about that. Thank you for asking the international community regarding this issue in Pakistan. I hope you would get valuable input from international pavement experts in the community.

    ------------------------------
    Sajid Raza, Registered Engineer
    Graduate Research Assistant
    University of Alaska Anchorage
    Anchorage, Alaska
    sraza@...
    907-223-5720
    ------------------------------



  • 21.  RE: Designing Sustainable Pavement

    Posted 01-21-2019 09:58 AM
    Edited by Tirza Austin 01-21-2019 09:58 AM
    ​Ejaz,

    In following the comments and suggestions made by all in the group regarding this issue, I found the comments interesting, and very valuable, and most of all, encouraging that so many pavement engineers were willing to participate. However, coming back to your original question of can we as design engineers, and subsequently, how should we, account for effects of overloading, and also the concomitant trend of significantly higher tire pressures, in order to mitigate the detrimental effects? Now one can debate the fact that it should be a law enforcement responsibility to curtail overloading, and should not be the responsibility of us as design engineers, but that in my opinion, is a matter for a separate discussion all together. To keep in mind, the primary purpose of asphalt wearing courses, and subsequent pavement layers such as base course, and/or subbase layers, is to protect the subgrade, by sufficiently reducing the stresses imposed by traffic loads. While we can only "improve" the load bearing capacity of the in situ subgrade to some extent for practical, and for economical reasons, the most effective way is to "add" layers. Hence, we should be designing the pavement as a "system," and consider each layer as a component within this system. The first, and most important input parameter is imposed traffic loading. All expected traffic loads needs to be converted to ESALs, i.e. 8.2 ton (80 kN/18kip) single axle, dual wheel tires, and future traffic loading in terms of expected number of these loads that the pavement needs to withstand, needs to be calculated. Expected "overloaded," or axle loads in excess of the standard, will also need to be expressed in terms of ESALs. In addition, the effect of such a wheel load should also be evaluated in terms of the stresses and strains it will cause in the respective pavement layers, in order to ensure that it will not exceed the allowable limits for that material, within that particular layer, i.e. evaluate the point load effects. Then, pavement structure needs to be evaluated and analyzed to determine appropriate material type selection, and thicknesses.

    ------------------------------
    Gerhard du Toit, PE (TX), Pr-Eng (SA)
    Pavement Engineer, 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
    ------------------------------



  • 22.  RE: Designing Sustainable Pavement

    Posted 01-22-2019 08:08 AM
    Edited by Tirza Austin 01-22-2019 08:07 AM
    Thank you.You have  explained the issue in a proper way, however, I am going to add we should calculate the stresses for 25 tons axle load instead of 8.2 tons and for tire pressure of 150 PSI and then check the resistance of materials right up to one meter below subgrade top then subgrade followed by sub base and unbound base. Maybe we need to improve the testing mechanism, for example, the modified proctor test will be needing further improvement on the same analogy as it had been upgraded from standard proctor to modified proctor. It will make the pavement layer stronger to resist the overloading. Similarly the capacity of equipment may also need upgradation. Because the compaction effort will be more. Similarly, the strength test of asphalt concrete may also need to be reviewed for withstanding to the excess loading conditions. I think you may have got my points. 
    I am again thankful to you for taking so much interest in my country's issue. I am really glad to see the interest of great pavement experts across the globe or resolving this important issue of developing countries. 
    Thanks and with best regards, 

    Ejaz Ahmad Khan 





  • 23.  RE: Designing Sustainable Pavement

    Posted 01-22-2019 09:48 AM
    Edited by Tirza Austin 01-22-2019 09:48 AM
    Fighter aircraft carry 400 PSI tire pressures.

    As for modified vs. standard Proctor, I agree that for "normal" soils, there is no need to let the contractor know there is such a thing as Standard Proctor, but if you are on muck in the valley, Standard Proctor is actually better for the existing soil. You are just going to have to stabilize the subgrade with flyash/lime/cement or bring in and place competent material to create a foundation to build on.

    ------------------------------
    Hans H. Coucheron-Aamot
    [Retired]
    Albuquerque NM
    (505) 897-2554
    ------------------------------



  • 24.  RE: Designing Sustainable Pavement

    Posted 01-14-2019 12:15 PM
    Edited by Tirza Austin 01-14-2019 12:14 PM
    You are experiencing the same issue that our county engineers in Iowa, USA experience.  Here the weight limits are "waived" during harvest allowing grain trucks to haul as much as they can hold and "farm wagons" have no limit.  My guess is that you will want to explore triage options on spot failures.  Design new pavements to be rehabilitation friendly.  Establish a strong foundation using local materials, geo-synthetics, chemical stabilization.. etc...etc.  so that when you have failures you don't need to start from square one.  Add structure to existing roadways if you have the ability to go "up". I don't think there is a magic bullet for this demon.
    I don't envy your challenge

    ------------------------------
    DeWayne Heintz EI, A.M.ASCE
    Project Manager
    L.L. Pelling Company
    North Liberty IA
    (319)626-4600
    ------------------------------



  • 25.  RE: Designing Sustainable Pavement

    Posted 01-14-2019 09:01 PM
    Edited by Tirza Austin 01-14-2019 09:01 PM
    The design that I have used for earth movers would involve fabric over plastic soils and then 3 to 6 feet of aggregate. Start with 3 feet and allow traffic to "test" and compact it. Then add aggregate in areas that rut or suffer distress.  The fabric should be placed to a width that will allow up to 6 foot of aggregate plus slopes on each side.  I would not pave until circumstances indicate a probable chance of load limits and enforcement of the same.  It is unfortunate that no credit is given to the road agency for providing a transportation route, traversing these areas by traveling cross country would be far more expensive, time consuming and dangerous.

    Fine sugar sand and non-plastic sands may require additional fabric at 1 foot intervals.


    ------------------------------
    Barry Anderson P.E., M.ASCE Retired
    Granite Falls MN

    ------------------------------



  • 26.  RE: Designing Sustainable Pavement

    Posted 02-08-2019 12:00 PM
    Edited by Tirza Austin 02-08-2019 11:59 AM
      |   view attached
    Dear Director Khan,

    Attached please find a relevant publication.  After reviewing it, you may contact me if I can be of any further assistance.  Thanks.

    K. Wayne Lee, Ph.D., P.E., F. ASCE

    ------------------------------
    Kang-Won Lee Ph.D., P.E., F.ASCE
    PROFESSOR III & RITRC DIR
    University Of Rhode Island
    Kingston RI
    (401) 874-2695
    ------------------------------

    Attachment(s)



  • 27.  RE: Designing Sustainable Pavement

    Posted 02-08-2019 10:42 PM
    Edited by Tirza Austin 02-08-2019 10:41 PM
    Thank you so much for your kind guidance and help. 

    Regards, 

    Ejaz Ahmad Khan