Backfill for Buried Pipe
Backfill for Buried Pipe
(OP)
I'm installing about 200 feet of 6" & 8" FBE coated steel pipe in a private unpaved lot. The design calls for a typical backfill for unpaved areas with native soil or sand per our company standards if native soil is unsuitable. Well the contractor discovered that the native soil was unsuitable for backfill and asked if he could backfill the 7-8 ft deep trench with wet sand slurry/ zero sack. According to the contractor, the slurry will flow alot better and will cover the pipe better compared to sand. Also, the issue with sand is shoring concerns in the future. Zero sack is basically just water and sand right? I asked some of the folks in the office and they were concerned about corrosion. Also they were concerned about the possibility of a sink hole without at least a 1 foot of sand on top of the pipe. The few that said no to zero sack had a hunch that the contractor was just trying to get out of labor intensive work of filling sand and compacting.
Since I'm still relatively new to the oil& gas industry, I really just don't know enough about the different types of backfills other than native soil and sand. From my research, there are several types of backfills that we use such as zero sack, 1 sack (contains cement), 2 sack, A & B (aggregate base), and popcorn. Can anyone be so kind as to explain these types of backfill, such as pros and cons or possibily direct me to a good resource. Thank You
Since I'm still relatively new to the oil& gas industry, I really just don't know enough about the different types of backfills other than native soil and sand. From my research, there are several types of backfills that we use such as zero sack, 1 sack (contains cement), 2 sack, A & B (aggregate base), and popcorn. Can anyone be so kind as to explain these types of backfill, such as pros and cons or possibily direct me to a good resource. Thank You





RE: Backfill for Buried Pipe
Independent events are seldomly independent.
RE: Backfill for Buried Pipe
addition of more than 1 sack of cement per yard is not generally necessary and may be detrimental since it makes it very difficult to inspect or repair a pipe encased in a high strength concrete.
sand bedding with jetting or flooding can be used, if the trench will drain out and if the contractor has the experience to do it right. It can be a suitable method of consolidating sand around the haunches of the pipe.
have never used AB for pipe bedding, sandy bedding material is generally easy to find, cheaper and easier to work with.
not sure what popcorn is. around here we have "chips" which is essentially pea gravel or pea size crushed rock and is a waste product when producing sand and gravel. It is a poor choice for bedding.
RE: Backfill for Buried Pipe
I've seen dry backfill watered to aid compaction so this is just a variation of that so long as the mixture is fairly stiff and only has the minimum amount of water to make it flow slowly.
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RE: Backfill for Buried Pipe
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RE: Backfill for Buried Pipe
Flowable fill is granular soil, usually native, with enough fines that it can be ixed into a slurry. Flowable fill reduces or eliminates problems such as uneven bedding, ring deflection, non-uniform embedment support, and voids under the haunches.
Flowable fill does not have to have concrete in it.
Here is a design document:
http://www.steeltank.com/Portals/0/pubs/Welded%20S...
RE: Backfill for Buried Pipe
With regard to your question, "Zero sack is basically just water and sand right"?, if you go to page 62 you will see that "flowable fill" is supposed to contain Portland cement and/or appropriate class fly ash etc. binder as well as sand aggregate to come up with the desired properties.
In conclusion I believe wet or slurried sand by itself and without working and/or good drainage may well not have a compressive strength of 40 psi i.e. 5,760 psf. While there are many sites that provide information regarding flowable fill backfill, as I suspect you have found there are not a lot yet that specifically elaborate on standard definitions of "zero-sack" or such mixes, and my only purpose with this further response here is to make sure it is understood at least some kind of further specification and "cement" (at least pozzolanic flyash) as well as properly controlled placement of the fill as others have noted may need to be provided in the mix for good pipe laying practice/support. It should probably also be further understood a flowable fill with only flyash and sand may develop its cemented strength generally at a somewhat slower rate than one that contains Portland cement as well.