Engineering Analysis Report (EAR)

[geomane]

My firm has been requested to perform an EAR for an FDOT project.

Project Info: the contractor has installed 27 drainage structures and has no compaction data. Here in Florida, drainage structures are required to be backfilled in 6 inch lifts and compacted to 100% pf the standard proctor. Pipe backfill is required to be 95% of the standard.

I was thinking performing hand auger borings with DCP testing at 6 inch intervals im the structure backfill as well as in the pipe backfill, and comparing relative densities. This has been accepted by the FDOT on our past projects. However, the problem here may be the difference in compaction requirements (i.e. comparing material compacted to 95% with material that is supposed to be 100%). I don't think tubes or drive sleeves would work. SPT's may be more economical than DCP testing due to the amount of tests that will be required.

Anyone have any recommendations for alternatives? Contractor wants to avoid digging down in 6 inch increments and testing with a nuke gage if at all possible.

 

[geomane]

Another option we may present is to construct 2 test pads (1 compacted to 95% and 1 compacted to 100%) 3 to 4 fee tall, test each lift with a nuke gage, and perform SPT's. Then develop a correlation between relative density and relative compaction. There is information in the FHWA Soils and Foundation Design Manual with similar graphs.

 

[oldestguy]

What are you doing about the lab Proctor tests? One point on each site sample?

 

[geomane]

Yeah, we would need to run some 1 point proctors at the structure areas to verify materials.

 

[Ron]

jmcc3265....you can use your approach. The FDOT does accept engineering judgment in most evaluative endeavors. I would correlate the DCP to actual compaction in the same material....do drive sleeves in the material near the surface adjacent to DCP and develop a curve. This will satisfy your premise development and meet the standard of care for such evaluations.

 

[EireChch]

My experience with DCPs in compacted backfill is that refusal will be met within the first 150mm approx? That was using a 7kg hammer with 550mm drop height. We classed practical refusal as 30 blows over 150mm (i.e. 10 blows per 50mm mark on the rod).

What method would you use to correlate the DCP results to relative density or MDD? I would interested to see the outcome of this, if you wouldnt mind sharing.

 

[geomane]

FDOT approved my work plan. In a couple of weeks I should have some data.

 

[geomane]

Here are the graphs we have created. 1 of 2.

 

[geomane]

2 of 2.

Unfortunately for the contractor, all of the storwater structure backfill has failed miserably with DCP blows of 3 to 5 on most everything we have tested.

As an alternative to digging around all 29 structures and replacing in 6 inch compacted lifts, I'm thinking some sort of grouting may be cheaper. Anyone use grouting for a project similar to this one? Of course it will ultimately be up to the DOT as to how the contractor corrects the deficiencies.

 

[geomane]

The graph for 1 of 1 should intersect the red (100%) line and the green (15 blows) line. I'm not sure why the best fit line moved when I posted the file.

 

[EireChch]

How did you develop that 15 blows = 100% compaction?

What are your blows, blows per 50mm or blows per 100mm.

Not sure if grouting would be my first choice. Low mobility grout and the likes expand, could this damage the pipe due to the increse in pressure.

If not too deep it may be easier to excavate and recompact?

 

[geomane]

EireChch - we pushed tubes and calculated unit weights then compared to the proctor value to get % compaction. We then performed DCP's adjacent to the the tube locations and plotted the DCP blows and % compaction at 6 inch intervals and then inserted a best fit line. None of the areas tested reached 15 blows, so the best fit line may slightly change if we had more data on the high side of compaction. But this is all the data we could get.

 

[geomane]

All the blows on the graph are blows required to drive the DCP cone 1 3/4 inch. We performed 3 sets of blows, each at 1 3/4 inch, and then used the 2nd set for our graph.