Statistical Compaction Acceptance 3

[Grouser]

With all this discussion of 95% compaction going on in the other forums, I would like to grind a personal axe and suggest that acceptance of compaction should be done using statistical methods rather than the pass/fail technique commonly used. If the mean of the test values met or exceeded the "specified" value, and contained no outliers more than x deviations, then the compaction would be acceptable. X can be defined as standard deviation units or as deviation from the "specified" value.

With the advent of nuclear testing devices, an adequate number of density results can be quickly obtained thus establishing sufficient population for the statistical procedure to apply.

Comments and alternative viewpoints welomed.

 

[l2grant]

AVG COMP >= Spec. + (1.65 -1.65/n^1/2)*STD. DEV.

I was just curious as to where this formula for the statistical method comes from. I am new to this field and am not to familiar with the statistical method of compaction testing. If anyone has any idea where this formula came from that would be great!

 

[BigH]

It comes from Ministry of Surface Transport (Roads Wing), Specifications for Road and Bridge Works, India. As to the "validity" - I am sure it has to do with ensuring that 98% (or some such percent) of the tests will have a relative compaction of 95% or more.

The one thing that I would also like to say - in big jobs and small - the most effective tool is still the two little round or oval objects each side of the nose! I find that it is not the "big stretch" say where material is laid in a 200 to 300m length for full width and compacted uniformly by a big roller - it is the little areas where, say, new fill butts up against older fill - or where the big roller can't go - or where the taper of a ramp meets with the main carriageway and the "end of taper" is hard to construct or where the grader operator has pushed material out over poor material that should be removed but the inspector misses it and the poor material is "left in place" as the tests show good results - but none were done in this last 5m or so. These are the areas that cause the problems. The more straight-forward no obstruction/no hindrance areas are a piece of cake. So . . . as my esteemed colleague Focht3 says, "Tests are not sufficient." This is why you have eyes!