Field Density Test after 6 Months

[tttmm]

Does any one heard about preforming a field density test to a compacted subbase after 6 months?
I couldn't find any thing on the net for a procedure.

 

[Ron]

A field density test can be performed any time. Why after 6 months? Are there other layers above the subbase? If so, the area that will have to be carefully removed to run and in-place density test can be quite large. Next, if using a nuclear density gage, you might have to compensate for trench effects.

As for the actual procedure to run the test, it is no different than that which would have been used at placement. There are several "indirect" measures of density that could be employed, with the clear understanding that they should be correlated to actual in place density. These would be effective if you had to run a lot of tests and could not expose large area for each of those tests. The most common of these would be cone penetrometer testing, either static or dynamic.

 

[dBasement]

Just keep in mind that the dry density won't change, but the moisture content will be a long way from optimum, so if there is any need for recompaction, you will need to get that moisture content back to the optimum range.

 

[AussieGeoEng]

I disagree with dBasement... if the soil swells or shrinks then your dry density will change. For example, if you have an expansive clay and it was placed dry of optimum and there was a wet period, then chances are that you dry density will have reduced (swelling), on the other hand if you have experienced a dry period then the material could have a higher dry density (shrinkage).

If this is a contractual issue then be very careful.

 

[dBasement]

He said compacted subbase, so I assumed granular. I agree that all the rules change with expansive soils.

 

[fattdad]

Just a comment to aussiegeoengineer: If it is a contractual issue and irrespective of the points about swelling and shrinking from moisture, compliance to the specifications is a contract requirement at the time the project is turned over to the owner. If testing is performed 6 months prior to substantial completion (passed) and in the week prior to substantial completion the owner retests and the material failed, the contract would require a fix by the contractor, not by the owner.

Otherwise all points seem to make sense to me. Granular soil should remain as tested (other than compaction moisture) and fine-grained soils could suffer, depending on the contractor's abililty to control the site.

f-d

¡papá gordo ain’t no madre flaca!

 

[oldestguy]

What sort of weather? If it is in an area that can have freezing temps and with some silts in the gradation, frost heaving can be large. In Wisconsin it is not unusual to find in the spring that what was compacted last fall is now very loose.

Of course test methods also can be wrong (not unusual for beginners).