Hilf density ratio report vs SDD requirement 2

[bakal28]

Hello everyone.

Our project requires subbase courses to be compacted to not less than 100% standard compaction. The contractor's compaction report submits a test report as Hilf density ratio being 102%. Can this be intepreted as compliant having exceeded the requirement by 2%? So for subgrade compaction requirement of 97%, the same interpretation applies.

Thanks for replying.

 

[Ron]

The Hilf method is a rapid determination which may vary from the standard method because of moisture content variations. I would require that the laboratory comply with the project specifications and perform the test in accordance with such specifications.

 

[bakal28]

Thanks for the response Ron.

Does that mean, the contractor used a different method of compaction testing? Is there a way of converting the 102% to standard compaction so I can check how much percentage achieved against the 100% standard compaction requirement.

 

[Ron]

The contractor's lab used a different method to determine the "standard" laboratory compaction. This method, though based on the Proctor method of determining the moisture-density relationship, is not the "standard" method of determining such a relationship and can present a difference in the comparision standard. For that reason, you could be comparing "apples and oranges", though the differences would likely be small. Unfortunately the small difference could mean the difference between passing and failing.

 

[bakal28]

Last one Ron. I've come across this practice before. What is the reason behind. Is it cheaper? Quicker?

 

[Ron]

Both!

 

[bakal28]

Thanks Ron.

Hats off!

 

[emmgjld]

Hilf Method is good for quick checking, used in addition to 'the Standard or Specified' method. I use it for fills that are going in quickly and questionable areas could be buried by the time x-checks are completed. Also good to identify minor changes in borrow material, which may involve changes of 1-3 lbs (oftentimes the difference between in or out of spec).
Like the entire practice of Engineering, knowing when something is being used or misused vital.

 

[bakal28]

Thanks emmgjld. When you say it is used for quick checking and used in addition to Standard compaction, does that mean, the result cannot be accepted as official if used as stand alone reference of compaction test outcome? How much margin of error are we expecting if we compare these results to Standard compaction test?

 

[emmgjld]

"does that mean, the result cannot be accepted as official if used as stand alone reference of compaction test outcome?" If the project specifications do not mention the test - It can't be official. My use of non-standard methods for checking or verifying are just that, a means of checking or verifying.
"How much margin of error are we expecting if we compare these results to Standard compaction test?" performed properly the Hilf method can be very similar to the Standard test. My experience, with soils in my area have been favorable.

 

[bakal28]

Thanks emmgjld. Big help.