Uhmm, NO!

Proof roll should be done just prior to proceeding with the next step in the process.

unless you want to prove that the surface is not ready for the next process.

to expand, earthwork and QA/QC testing should generally not be done in the rain or when the ground is saturated.

You could do it to prove that it's not suitable.

Has anyone ever seen a spec or method detailing how a proper proof roll should be done?  

I was taught by watching some of my superiors and listening to their recommendations - so I guess I've always thought of proof rolls not being very scientific, but based almost solely on the engineers judgement.  

For example, if it did rain recently and the base stone for a roadway moves a little bit, I will be willing to let it go if there is 9" of asphalt going on top since it may be bridged by the BBC, but would be much more weary about it if there are brick pavers placed directly on top for a brick roadway.

Also, if there is a very small area that moves a good bit and it is surrounded by base that does not move at all, how do you correct that?  In the past I have the contractor dig it up and replace with a section of 3" rock, but then after you measure the quantity for unsuitable material removal and replacement, I always realize that there is no way the contractor is making any money from having to do that with such a small area [not that I feel bad for them making all that profit :) ]  Usually this may be near some small utility repair which needs less than a truckload to remove materials and bring in 3".

I found several specs for proof rolling for various conditions.

1) To identify limits of pumping subgrade
If pumping subgrade should become evident at any time prior to paving, the Engineer may require proof rolling with a pneumatic-tire roller or other approved equipment in order to identify the limits of the unacceptable area. The proof rolling will be performed at no additional cost to the Contracting Agency.

2) For reinforced earth fill construction
Foundation soil shall be excavated to the lines and grades shown on the drawings or as requested by the Engineer.  Over excavated areas shall be filled with compacted backfill material.  As a minimum, foundation soil shall be proof rolled prior to backfill and geogrid placement.

3) County road spec
Proof roll prepared subbase surface to check for unstable areas and areas requiring additional compaction.  Notify Engineer of unsatisfactory conditions.  Do not begin paving work until deficient subbase areas have been corrected and are ready to receive paving.

4) Design Build spec at an airport
Material exceeding the gradation requirements of ASTM D 1557 shall be compacted to non-movement with equipment specified for proof rolling. Proof rolling of subgrade shall be performed with a pneumatic-tired rolling equipment, developing, a load of 30 to 50 tons. Proof rolling shall only be performed in the presence of the Engineer. In a systematic manner acceptable to the Engineer, the equipment shall perform a minimum of three (3) passes over the designated areas(s). When proof rolling of the subgrade shows an area to be unstable as determined by the Engineer, the unstable material shall be removed and replaced to the limits designated by the Engineer.  

5) For a flood control channel
The channel bottom shall be proof rolled using rubber tire equipment with a gross vehicle weight of no less than 30,000 pounds. Proof rolling shall be conducted with no less than two passes with overlapping tire path and shall be witnessed by the Engineer.

6) For checking of subgrade conditions in cut areas
In lieu of recompaction of the subgrade in cut areas, the CONTRACTOR may proof roll the subgrade with pneumatic-tired rolling equipment developing a load of 30 to 50 tons.  In a systematic manner the equipment shall perform a minimum of three (3) passes over the designated areas.   When proof rolling of the subgrade shows an area to be unstable as determined by the OWNER, the unstable material shall be removed and replaced to the limits designated by the OWNER.  Removal and replacement shall be in accordance with Section 2.2D.

Thank you for the spec reply cvg.  Those all make sense for each application.

However, I guess I was looking for a more detailed answer on what specifically you look for in a proof roll to determine the subgrade as being unacceptable?  I know that you typically look for rutting, pumping, movement at soft areas... but what about if you proof roll an area of sandy clay that doesn't really move, but still creates ruts from the semi tires that you used for the proof roll?  At what point do you decide that it needs to be removed or just needs to be dried out and recompacted?

I'm wondering if there are any guidelines or charts that you could reference and give to someone that is just starting.

My recommendations usually are a combination of the soil boring logs data/undercut recommendations and knowledge of what I've seen in the field in regards to the type of soil, moisture content, and rut depths.  I feel lucky to not have needed to cut out more areas after the subbase has been capped with a base layer of stone and proof rolled with a fully loaded truck.

Also, I've never heard of proof rolling subbase with an empty truck until I read it somewhere on these boards.  Has anyone had success with doing this, then placing base stone, and proof rolling with a loaded truck?  Again, I would hope to not have to do undercuts twice, so I guess that when I use a fully loaded truck on subbase, I'm being pretty conservative...

skillz,

See the following links:

http://www.dot.state.oh.us/construction/OCA/Specs/2005CMS/200/204.htm

http://www.michigan.gov/documents/MDOT_ProofRolling_61181_7.rtf

Ruts should be limited to about 1/2 inch or less and should not get progressively deeper with increased number of passes(otherwise indicates punching shear failure through soft material, right?). Pumping is trickier, as it indicates that a buried layer is overwet or oversoft. It can be difficult to determine the lateral and depth limits of overexcavation and replacement.

Jeff

Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com