self-compacting gravel? really?

[benirvine]

I am preparing an interlocking paver driveway and have filled 6-10 inches with 1 1/2 inch down to 1/2 inch washed but angular gravel with no fines. From what I have heard on the forum and elsewhere, this approaches a "self-compacting" gravel. Can that be true? I understand how rounded gravel self-compacts (the marble story), but I would think that vibrating the angled pieces to interlock and perhaps adding 1/4 inch minus crushed gravel would fill voids and lock it in tight. Any opinions?

 

[boffintech]

The use of plate compactor in this instance will greatly help “lock in” the angular pieces. The addition of fines will inhibit drainage so if this is a concern, don’t do that. Additionally, a plate compactor is typically run over the pavers after you put the sand on them and that would be a heck of time to find out that the #57 stone could in fact be more densified. Run the plate compactor over the stone now while you have the chance.

 

[emmgjld]

boffintech has some very good advice.

In some localities, the # 57 Stone and other poorly graded (geologist-well sorted)gravels and sands have been utilized as 'self compacting' stabilizing aggregates with an excellant track record. In some other parts of the world, disasters have resulted. I recommend you approach 'self compacting' aggregates with care. I recommend keeping the materials as thin as possible. Moisture conditiong and compacting should occur when ever possible.

My own experience is quite negative. In my part of this globe, 'self compacting materials' is a Faerie Tale. But is widely belived. The excuses for the obvious and not so obvious failures are numerous.

For those who want a little background, the disciplines of Sedimentary Geology and Petroleum Geology deal with the particle 'packing' and organization. It can be a real eye-opener to discover the wide range for particle packing in 'nature'.

 

[MPENN]

I have consulted (never a fee) to a childhood friend for nearly 35 years. His business does very well. About twenty years ago he installed a sixty foot truck scale. The foundation height was about four feet. His contractor, (also a PE), suggested using crushed stone (minus 2") as a backfill around the foundation, it would interlock and not need compacting (saving time and effort). I advised using gravels place in well compacted lifts or at the very least, please compact the crushed stone. Notfornothing, the crushed stone compacted "over time" from wheel loads and vibration. Each time I stop by and visit I am visually reminded of his contractor's advice.

 

[dicksewerrat]

to those of you that believe that material will compact by the force of gravity, don't design foundations or trenchwork in the road.

 

[RCEJD]

Gravel when dumped does not self compact. It is just that under most applications it is not subject to excess settlement due to arching or the in place density.

As dickwewerrat correctly alludes to, if the gravel is subjected to dynamic loading (or larger static loads) it will settle (i.e. thinks of why you compacted aggregate base for roadways).