Proof Rolling.....What? When? and How much? 1

[jsullivan52]

As part of the new city codes the city is requiring proof roll test on all new streets that are to be later dedicated to the city by the developer. On top of our normal QC/QA testing produceres. My question is what are some of the acceptable practices.

1) At what distance from the road surface should you be able to see movement? And is any movement allowable?


(We usually use a binder 19.5 mm asphalt mix then come back later into the development after construction loads have settled to lay a surface mix.)

2) Does a little movement (by little I mean you need to be on your knees and have the truck pull up and back up in order to notice it) in the sub-base material (limestone) matter in the long run?

3) Does movement automatically mean sub-grade failure? How can you tell if the problem is in the sub-grade pumping or just not enough compaction in the sub-base granular material? I understand the large movement pretty much means sub-grade, I am wondering more on the specifics of small non-yeilding movements.

Thanks for the advise!!

 

[LCruiser]

A lot of times immediate pumping is due to excess pore pressure - especially if proofrolling is done without giving that pressure time to disperse. Each soil is different. So, no, I would not necessarily say pumping means failure, but it's definitely close...

Distance out to movement varies with the soil strata.

 

[msucog]

1) movement is not good...but not definitely "failing"
2) "little" movement may not be a big deal depending on what it is due to. "in the long run", a pavement's performance is dependent on many factors beyond whether it holds up one or two passes with a LTADT
3) in some soils, a LTADT on the subgrade may cause surficial failure because it's so crappy as subgrade material...even if it is well compacted...but that same soil does "ok" if base course aggregate can be placed on the undisturbed material. pumping usually means not good subgrade soils...if the base course aggregate needs additional compaction, it will usually leave small ruts with no pumping.

proofrolls are subjective and almost always variable due to the different soil conditions that can exist. proofrolls are also difficult to fully explain...especially when considering all the factors at play to make a long lasting pavement section. have a trained geotechnical (or other qualified) engineer show you good, bad, ugly, perfect, etc...then have them explain how each of these situations can change dramatically based purely on the people involved in the project and everyone's expectations. i suggest that you always stay of the side of caution because a mistake or unidentified problem costs lots of money to fix. where ever possible, perform testing to design the pavement and to check in-place field conditions.

check the state DOT websites since they quite often have manuals on pavements. good luck.

 

[fattdad]

Here are my thoughts on proofrolling a binder surface. You have no idea how much surface water infiltrates binder asphalt. I did a simple-simon permeability test on binder asphalt and got a permeability of about 1E10-2 cm/sec. That's high. A properly-prepared soil subgrade (i.e., proofrolled/compacted structural fill or native ground) and the overlaying aggregate base, can become fully saturated by this infiltration. If you then proofroll, when these materials are saturated, you can bring on your own construction-related disturbance and failure of the otherwise suitable (partial) pavement section. I always feel that the practice of using the base-mix asphalt for the benefit of the contractor is an uncessary risk to the specified materials to the owner.

On the matter of rutting, pumping, weaving, etc. judgement is required, but none is great!

f-d

¡papá gordo ain’t no madre flaca!

 

[jsullivan52]

Fattdad,

We aren't proof rolling the binder. I just stated that because that is what will being going over the sub-base material and then we will wait for the constrution traffic to settle before applying the surface. We proof rolled the sub-base material and the city inspector noticed some movement and so now the contractor has to fixed the problem. I am wondering at what point do you decide to "fail" a proof roll. The area that was failed was about 3' by 6' and movement, if i had to put a number on it, was about a quarter to one half inch in the vertical direction and spread out maybe a foot. (not sure if thats how you measure or not)

Sorry about the confusion

Thanks!

 

[civilperson]

Easy fix is to over excavate the failing area 24" below the base course and replace with 8" lifts of crushed rock compacted with vibrating steel wheel roller or jumping jack tamper. Repave and retest with front wheel of water truck to proof roll. Works every time in my experience.

 

[fattdad]

We aren't proof rolling the binder

Yeah, I guess it may not make sense why I said that - sorry. We were working a project where the binder was used to support construction traffic. I mean the binder got really messed up from all the LULLs and construction staging. So the owner had the entire binder proofrolled and in the process, cracked up the entire parking area. The original damage (i.e., from construction) too place in the winter and the proofrolling also took place when the binder/base aggretate was completly saturated. It was a huge mess!

front wheel of water truck to proof roll

I'd use the back wheel of a water truck. But, I'm always looking for trouble. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[civilperson]

Usually, the front wheel tire pressure is highest and the weight per wheel is also highest on the front. If axle weight is your criteria, then rear dual wheels can be heaviest per axle.

 

[LCruiser]

Depends on the depth in question. The point load a a single front tire may be greater at the surface, but if you're looking for a problem at a foot or two or more down then the back wheels will be the more substantial load. Best to use both.

 

[fattdad]

What LCruiser said.

f-d

¡papá gordo ain’t no madre flaca!

 

[jsullivan52]

I have another question pertaining to this. The Proof Roll failed and now the contractor is to repair the fail areas which is most of the Cul-de-sac of a residential subdivision. Would it be best to place the whole Cul-de-sac area since it is the majority of the area? The contractor claims the soil below the subgrade was saturated with water from an water leak. What would be the best way to repair the situation. If we took out 2' of material and backfilled with clay gravel does density need to be obtained at the 2' depth? What are the best compaction methods in these situations?

Thanks!

 

[cvg]

you need to get your geotech out there to evaluate the new subgrade (2 feet below) after you excavate. have him evaluate the in place density of the material as well as moisture content. don't begin until it has dried out. you may be able to use the native as backfill if it is dry and deemed "suitable" by the geotech.

 

[msucog]

maybe have the geotech take a look at it before the repair if the contractor isn't picking up the tab to undercut and replace the area. it might turn out to be a 6" problem but the contractor wants to get paid for 2'. it might also turn out that it's obviously poorly compacted fill instead of a water leak. there again, it's very possible that the cause cannot be definitely determined so you're stuck taking the contractor's word for it (which i know not to do if i can help it...sometimes, you're just stuck if there's nothing to prove otherwise).

and yes, whatever goes back in needs to be placed in thin lifts and thoroughly compacted (my idea of thoroughly is certainly different than contractor's idea of the word). consult with a geotech if the contractor isn't paying to fix the area. if they're fixing it at their expense/headache, i'd consider not getting a geotech until the next time it fails proofroll.

 

[jsullivan52]

Its one of those deals where the contractor is the owner. So they are paying for it either way. They undercut three foot and found some pretty bad clay about 1'-1.5' below top of our subgrade and extremely wet.... There is some good sandy soil, with a proctor that ran 111 pcf and optimum moisture around 15%. I got some samples of the clay and are in the process of running some test. What should I look for in the clay tests to see if the clay is fine to fill in the three foot with onsite select fill and 1' of clay gravel?

Thanks