Consolidating 3/4 " Gravel
Consolidating 3/4 " Gravel
(OP)
Hello all,
A project we are starting next week requires 95% compaction on a 9" section of 3/4 " crushed aggregate under the pipe as well as thru pipe zone section. The pipe is 24" h20. As a technician, I have never actually tested the rock for density. Usually would just recommend the contractor run a vibratory plate over the bottom rock a few times, back-fill to spring line, hit again and then once more at top of pipe zone. There will be approximately 4 feet of soil cover over top of pipe zone.
Any suggestions as far as testing rock, or for that matter achieving the 95 % requirement ?
Thanks for the help................
BG
A project we are starting next week requires 95% compaction on a 9" section of 3/4 " crushed aggregate under the pipe as well as thru pipe zone section. The pipe is 24" h20. As a technician, I have never actually tested the rock for density. Usually would just recommend the contractor run a vibratory plate over the bottom rock a few times, back-fill to spring line, hit again and then once more at top of pipe zone. There will be approximately 4 feet of soil cover over top of pipe zone.
Any suggestions as far as testing rock, or for that matter achieving the 95 % requirement ?
Thanks for the help................
BG





RE: Consolidating 3/4 " Gravel
Maybe I'm just too practical. . .
f-d
¡papá gordo ain't no madre flaca!
RE: Consolidating 3/4 " Gravel
ASTM has a procedure refered to as "sleeve density" to test such materials. The USBR developed this procedure to be able to reasonably provide some numerical means of assessing relative density in poorly-graded granular trench backfill that were not conducive to sand replacement or nuclear inplace density procedures.
http://www.astm.org/Standards/D4564.htm
The other item is that cohesionless soils are often tied to laboratory compaction procedures more appropriate for fine-grained soils. A poorly-graded granular soil with few fines should really be evaluated by the relative density mehtod, based on the maximum density by vibratory methods (D4253 - Maximum Index Density of Soil).
One approach I've used to communicate with a contractor on the degree of compaction in trench backfill was to use a concrete vibrator. We inserted a concrete vibrator when the backfill was at pipe springline and let it go; the vibrator quickly penetrated the backfill, as well as created a cone of depression around the vibrator. The contractor saw this and recognized that the backfill was not well compacted in the haunch at all (which was significant for the large diameter flexible pipe). Not wanting to revisit the project later, he had two laborers compacting the backfill until it resisted penetration by the vibrator.
Since your degree of compaction (95%) is relatively high, I would not expect a well compacted granular backfill to settle at all under vibration.
Good luck!
RE: Consolidating 3/4 " Gravel
Dirtdelight, you need to verify if proctor or relative methods are to be used. If "relative", than verify they need 95%. If "Proctor", check with the state DOT manual to determine the appropriate test methods for aggregate base.
RE: Consolidating 3/4 " Gravel
i've seen this on plans before and it turned out to be an unknowing civil drafter sticking "95% compaction" everywhere that had some form of fill/backfill. it sounds like the stone is for bedding purposes. the contractor should put in the bedding stone, bed his pipe, then backfill with a very thin layer of soil then compact with a jumping jack/wacky packer. being that thin, they shouldn't have a problem sufficiently densifying it with a jumping jack. if they're using a plate tamp, then they'd probably better put in the 1st 4-6", run the plate over it then put the rest...then throw the pipe in and backfill/compact from there.
RE: Consolidating 3/4 " Gravel
Thanks again
BG
RE: Consolidating 3/4 " Gravel
In this case, I'm inclined to believe that a couple passes with a walk-behind or backhoe vib plate is all you need. After all, it's pipe bedding, not a highway fill or the foundation for a skyscraper.
RE: Consolidating 3/4 " Gravel
RE: Consolidating 3/4 " Gravel
Don't ask me what to do with Modified Proctor data!
Irrespective of the specification, I'd agree witn dgillette, 2-ft lifts and a couple of passes with a vibratory roller would be o.k. by me.
If surface water infiltraiton is not an issue and there is no ground water to speak of, I'm not sure I'd use the separation geotextile.
f-d
¡papá gordo ain't no madre flaca!
RE: Consolidating 3/4 " Gravel
RE: Consolidating 3/4 " Gravel
RE: Consolidating 3/4 " Gravel
RE: Consolidating 3/4 " Gravel
RE: Consolidating 3/4 " Gravel