self compacting #57 stone...again?! 1

[msucog]

this is more of a reminder for those threads that are buried deep in pages that never get seen anymore. #57 stone (or any other aggregate) is NOT self compacting...it is far from it. this topic always manages to come back around and i'm always lost for words at how many people blurt out "it's self compacting and has been for the 15 years i've been doing this". this is one topic that continuously starts a fight because everyone thinks they're right. i have plenty of data to prove that it is not and will put up my pay check in a bet any day of the week. if you think that your project may utilize crushed aggregate, please do a search of threads on eng-tips and read up...there has been many discussions on the topic. better yet, just think about this:
1. is silts/clays self compacting? no
2. is sand self compacting? no
3. is rock fill self compacting? no
4. so why would anything in between be self compacting?

when you do a search, you can actually find threads where i've passed along quick and dirty ways to prove it to yourself. your techs, engineers and company will appreciate the fact that you're not exposing them to ridiculous mistakes. 75% of all forensic investigations i've done related to foundation problems involved #57 stone...

if anyone has formal references, papers, articles, etc that discusses this topic, i surely would appreciate if you could pass along the link. i'll continue looking. maybe i'll write an article for publication backed up with field examples and lab data. this topic comes up on just about every single cmt project.

best regards

 

[Ron]

msucog...always worth repeating....agree completely!

 

[hokie66]

While you are on the subject of self compacting, maybe you can clear up something from the deep recesses of my ever shrinking brain. In the old days, compaction of sand was often specified to be done by "flooding". I never actually witnessed it, but wondered how effective it was. I thought you could compact sand by dumping it into water, but not the other way around. Old wives tale?

 

[msucog]

you can hokie66. you get a lot of compaction by flooding. quick experiment: take 5 gal bucket. fill with clean sand (tamp or not tamp your choice...try both). then add water and see what happened. after you're amazed, gently tap the sides and watch the magic. the water lubes up the sand particle and imparts just enough pressure to allow it to move around and fill the voids. you can 'always' improve compaction depending on the effort put in to the system...the higher the compaction, the more effort you have to put in to see improvement.

sand is not self compacting though so don't misinterpret the term...it's basically liquefaction. liquefaction doesn't "just occur" since there has to be some energy applied. self consolidating grout...you pour it and it's done. it doesn't work that way with soil, sand, silt, clay, aggregate, rock etc.

 

[Ron]

In order for the wet method to work in sand, you have to have permeable material below it. It is the "suction" and lubrication created by the vertical drainage that "compacts" the sand. As msucog notes, you don't get a lot of compaction, just mostly consolidation from re-orientation.

 

[BigH]

We actually used river sand behind retaining walls in Vancouver on Skytrain construction - - used flooding techniques. The Fraser River sand is very free draining and we had some 20 m of head and the water could "escape". Interesting that the Vancouver Specifications forbade flooding for compaction - yet their own crews did it almost everywhere I saw . . .

 

[dgillette]

That was a routine method for embankment dam shells and drains at one time. Makes us a bit nervous, however, when we come back many years later after discovery of new active fault close by, and we start thinking about settlement, excess PWP, and that kind of stuff.

 

[cap4000]

Take a look at the link below. In Nothern NJ with #57 stone the DRW and Unit Weights simply dumped are around 90% compact +/-. Braen Stone and Eastern Concrete are the suppliers. 89/100 and 88/98. Generally a small walk behind plate compactor is used also to increase the compaction.

http://www.state.nj.us/cgi-bin/tran...portation/eng/technology/materials/MATDB.shtm

 

[valleyboy]

This has puzzled me also! If you have a look at the following link to the 'earthworks' section of the UK Specification for Highway Works, Table 6/1 states that for material type 6A that no copmaction is required. I note that the typical use is stated as 'below water'. I assume then that compaction is achieved by the principle of flooding as described above?

Table 6/2 shows the grading for the material is 5mm to fine material?

http://www.standardsforhighways.co.uk/mchw/vol1/pdfs/series_0600.pdf

 

[BigH]

VB - thanks for the link. I've seen this before - this is "fill" dropped into water. Unless one drains the pond/stream muskeg or whatever, you'll never be able to compact anyway - so this is a "base" on which the embankment foundation above the water would be placed - it doesn't have to be, necessarily, select granular material. I don't think that by dropping the 6A through the water will "compact" as in flooding - and they don't expect it too - it is an "expedient".

 

[msucog]

test it in a real field situation and see if you'd feel comfortable stamping your career on it. try the simple rodding experiment i've explained in detail in other threads and see if it doesn't convince you that non-compacted #57 stone is problematic. again, the vast majorities of problems i've seen are related to loose crushed aggregate. hell, build a box 1 foot high and lay it on top of the crushed aggregate fill area then have the trackhoe dribble aggregate until it's filled over the box. then carefully hand remove the stone and see how much it weighs. then do it again with light compaction and see what the difference is. without even getting off in to the strength characteristics of each approach, the unit weight difference should scare you. i've done it...seen it...worried over it...and been bitten by it. if the contractor was placing clean sand, would you let them get away with no compaction? now just scale that up to aggregate size...what's the difference? and if it were self compacting, why do geopier contractors beat the hell out of the aggregate? there's a million examples i can give to compare to the scenario. don't believe my ramblings...try it experimentally yourself and prove it to yourself.

 

[BigH]

From what has been said, as I noted above, is sounds like the embankment will be constructed in a swamp or muskeg or very shallow pond. It is not a matter of putting stone in and not compacting because you don't want to compact - it is impractical to "drain the site" in order to place fill in an engineered manner - i.e., in lifts, compacted, etc. So, as a result, a clear stone or fine (even coarse) rock fill is dropped through the water until it is above the water to form a "better" base onto which to properly construct the above water level embankment. Of course, this is taken into the design of the embankment.

Read the case history by MAJ Matich et. al. on the construction of the Rainy Lake Causeway - at this site they had fairly shallow water but the foundation soils were soft varved clays/silts. The stability of the embankment if placed directly on the material would be suspect so a program of blasting the soils to remould in order to dump rock fill and displace - without compaction - was used. This same technique, known, too, as the rolling surcharge (See Michingan DOT article in 1946) does not compact a road embankment in a swampy portion of the site until the "base" is able to support the compaction efforts.