Backfilling corrugated pipe {caisson}
Backfilling corrugated pipe {caisson}
(OP)
In loose sand and gravel {5-8-5 blows per six} we are advancing 42” steel pipe to 15 or 16 feet. After steel pipe is set permanent 36” corrugated pipe {CMP} is set. After 36” CMP is backfilled with existing drilled spoils, the 42” casing is extracted. A steel plate is set on the 36” CMP and vibrated with a plate tamper for approx 5 min. After vibrating any annular space is filled and CMP vibrated again. I have used this method on other projects with similar conditions, but I need to convince the field engineer this is a viable alternative to flow able fill. Any comments or suggestions appreciated.





RE: Backfilling corrugated pipe {caisson}
Zambo
RE: Backfilling corrugated pipe {caisson}
Hypothetically, your technique should be able to achieve the desired result under certain conditions. But I suspect that the amount of "brain damage" to the field engineer - over a fairly small (trivial?) cost - doesn't seem worth it to him. After all, if he approves it then he could be expected to help pay for any repairs should it be unsuccessful. I don't blame him - in most situations I'd probably do the same thing.
RE: Backfilling corrugated pipe {caisson}
RE: Backfilling corrugated pipe {caisson}
Perhaps you could do a SPT in the backfill and compare to adjacent material?
RE: Backfilling corrugated pipe {caisson}
That's a lot of 36" CMP! Are these footings? Are they filled with concrete?
Anyway, back to your problem. There are flowable fill purveyors that can provide a mix that's completely set in only 3 or 4 hours, and is "hard" in an hour. They custom mix on site in whatever quantity you need for that location, so there's no waiting for a truck from the batch plant. (It's a self-contained batch plant on wheels.) And the material will achieve a minimum strength of over 100 psi, which will be as strong (or stronger) than a granular backfill. Stronger mixes are available if you need the extra strength.
Give the engineer notice that you intend to begin work on a date certain, with placements every working day until {whenever you think you will be finished}. This really will be faster than your compaction technique - and cheaper in the long run.
RE: Backfilling corrugated pipe {caisson}
Interested to know what these are. Access chambers?
Zambo