Specifying compaction testing
Specifying compaction testing
(OP)
I have a project where I'm being asked to specify compaction testing - type, when, where and how many for the backfill over a newly installed sewer (10-16' deep). We need to insure 95% compaction. What is the best/practical way to do this?
Thanks for any input.
Thanks for any input.





RE: Specifying compaction testing
are you responsible for quality control or quality assurance? ie: are you working for the contractor or the owner?
also, is this in right of way, existing or new street, what type of soils and what type of bedding and backfill material? what type of pavement? installed in trench or posative projecting? what type of equipment is doing the compaction? is this a local street or a highway? what country? what type of pipe? what does your permit require?
RE: Specifying compaction testing
Project is in Northeastern USA.
Installation is new sewer under existing local street (private). The testing agency is responsible for quality assurance and will be hired by the contractor who is responsible for quality control. My spec. is for the contractor with the purpose of giving the owner what they want. The pipe used will be 10" SDR-35, bedding material is 3/8" stone, backfill material will be the excavated material which is sand w/ trace to little silt. Compaction equipment is up to the contractor.
Hope this helps.
RE: Specifying compaction testing
RE: Specifying compaction testing
RE: Specifying compaction testing
Also, the lift of trench backfill thickness (Backfill above pipe zone, pipe zone backfill being separate) we have dependent upon the class of backfill (ie Class A, C, D and E). They seem to vary from 6" to 8" lift thickness max.
Don't allow free fall of backfill into trench until at least 2 feet of backfill has been placed.
Do not allow power driven impact type compactors for compaction unless at least 4 feet of backfill is placed over pipe.
Anyway, there are a whole slew of considerations in the trench backfill specifications that I didn't include, but here were just a few.
RE: Specifying compaction testing
Backfill after that point with native material, 1 test per 1000 sf, every 6". Sand cone every day is excessive, but it's up to you.
RE: Specifying compaction testing
if you're really concerned about compaction, the testing should accompany onsite observations of the fill placement procedures. and contractors being the "fine" folks they are (i.e. sneaky), i'd suggest having someone onsite full time. some budgets don't allow for this so part time testing is all you get. so if the tech is onsite say 2 hours per day, then you've got test results to make someone feel good about what is there. in reality, you're most likely not seeing the less than desireable stuff going in place.
for part time testing, i suggest budgeting for half a day each day at a minimum. again, i suggest full time testing. either way, make sure it is in the specs that the contractor is responsible for scheduling the testing firm as needed and that evaluation/testing should be performed at least every 2' vertical lifts for every 150' or so. lifts using small mechanical hand tamps should be 4" thick max and lifts using larger equipment can be 6"-8". you might get by with slightly thicker lifts as mentioned by others but i personally wouldn't spec thicker (the contractor will always manage to sneak a few extra inches in to each lift unless you've got a someone standing on top of him watching). i'd also suggest including a remark about moisture content (generally +/- 3% of optimum typically works well but might needs adjusting depending on your specific soil conditions). also note that safety and means and methods are the sole responsibility of the contractor. i quite often seen deep trenchs with no trench box so how the heck is anyone going to compact much less test such a scenario? even if they have a compactor attachment for their trackhoe, someone still has to test the stuff so safe access is essential.
good luck
RE: Specifying compaction testing
About a 2-3 sack mix, +- 150psi sets up in a couple of hours, look at the batch tickets, done! Pave!
Yes, you will pay a bunch of $$ for the mix, especially since this is a sewer and it is deep. But, run the numbers, you may be better of financially this way. As a side benefit, you will get to know your local concrete producer very well.
RE: Specifying compaction testing
A common spec for trench fill in streets is something like 90 % up until the last 5 feet and then 95 %, and it may be difficult to get, especially if Modified Proctor is your standard.
No one said anything about how many lab Proctors to do? One? One per ten FDT?
I'd sit back and see what you really need for the site. Is there some guarantee of filling of depressed pavement in case the testing is skimpy?
If it is sand fill, some communities have done jetting of the backfill and no tests and it has worked out fairly economically, with some subsequent pavement settlement. But who is paying the bill. A lot of items need to be considered.
RE: Specifying compaction testing