Roadway Pavement Section Change Frequency

[LCruiser]

Hopefully I can get some input here. I'm wondering what the accepted minimum length of a pavement section change is. For example, the first half of a contract is in a valley with low R-Value subgrade and the second half is in the mountains with a more competent subgrade. Rather than design the road with a consistent section (say 5" HMA / 8" AB) how frequently (e.g. every no less than one mile) do you change the roadway section, to take advantage of the mountain subgrade and enhance the section in the valley?

 

[BigH]

Several questions, my friend. If, as you indicate, you have two distinct sections, I think it is pretty obvious. If you go from one to the other and back again and again, it is a different story. In the valley, are you going to be putting in a small embankment for the roadway (even for a metre or so)? If so, then it would be the R value of your embankment material, not the valley bottom that you would use for design. I would never build a section 'at grade' in a valley - drainage would dictate a small embankment.
But to get back to the change frequency, keep in mind that someone has to build this - and to change from one section to another over short distances can lead to many headaches for all involved with the on-the-ground construction. For a new road, I would have an absolute minimum of 200m sections and even 500m lengths would be better. This gives the contractor a good 'length' to build of similar materials. Too, you will also need to think about transition zones. For a reconstructed roadway - I would probably use 1000m lengths for pavement sections as a minimum.

 

[LCruiser]

I was thinking 1 mile sections, and the contractors I've talked to say it's not a problem. Sounds more like lazy or overpushed designers or surveyors. There is a lot of money to be saved for the extra "work".

 

[emmgjld]

Depending upon the size and complexity of the project, my 'break point' ranges from 100 to 500 ft. This depends upon:
--The amount of change. 2" vs 6" of grade difference may represent very different economies.
--The quality and capabilities of the Contractor. Some contractors create more trouble than the effort is worth.
--The project complexity. Lots of utilities, manholes, drainage plans, etc. may result in more problems than is worthy.
--Last, but sadly, not least. The quality of the Civil Engineer and Surveyor.

 

[civilperson]

The frequency of the soil tests should be at least every 500 feet and the the worst case design section should be used until the soil strength test is surpassed by double the standard deviation of the "weak type of soil". Alternate bids could be entertained for soil improvement methods to be used with the less expensive section of pavement.