Options to remedy low MC backfill

[cr1973]

Our contractor completed a small pipeline project, backfilling the trench with a predominantly sand material which also included some stone as well. Upon having several compaction tests taken, the material was seen to fall in the 90 to 95 percent range, failing our required 95% modified min, which I believe was due to a very low MC.

Aside from tearing up the backfill, replacing with suitable material, and re-compacting, are there any other options? Would flooding the trench cause more harm than good?

 

[oldestguy]

For one thing using the term "compaction tests" probably meaning field density tests, brings up some questions. Regardless, what is this job for? Why 95 percent any way? Are there buildings to be placed on it? If the nuc meter is used, is it calibrated for this material? A common problem for nuc's is they may not truly give correct results. Does the laboratory test truthfully apply to the site material? For sands, moisture content sometimes may or may not be critical. I'd look at each factor in the evaluation and make sure it is correct. Before getting too nasty, bring out the calibrated sand cone equipment and run some tests.

 

[cr1973]

oldestguy:

The trench is located within the road right of way which is to be paved in asphalt. The testing tech took a proctor from the stockpile for comparison, so we believe the material in the field matches closely to the proctor. Some of the results were in the mid 80%s as well.

 

[Ron]

To be that far off in field density, even with moderate compactive effort, implies that your Proctor value varies from the field condition. Take a sample from the field and run a check point on the Proctor curve. It should match closely. If not, run another Proctor from the field material, not the stockpile.

What are your Proctor values and what are your field moist contents?

If you are using a nuclear density gauge, make sure your technician knows to compensate for the trench sides. Also, make sure you do a moisture content by a supplementary method as a check against the nuke.

 

[cvg]

first of all, every lift should have been tested. testing after the final backfill is complete is inadequate. 80% is totally inadequate. in our region we would require 100% for the top 2 feet. So how do you now check compaction in the haunching and initial backfill zone? Flooding may or may not work depending on how clean the sand is and how deep the trench. jetting might possibly be better. but not sure how you will perform the QA. If this is in Right of Way, I would suspect that you need to satisfy the city inspector and it will probably get ripped out and redone.