Compaction of River Shingle 1

[gortech]

River Shingle is frequently specified for placement below road bases and embankments on weak ground or in wet subgrade conditions. The grading characteristics of river shingle can lead to some difficulty in achieving good compaction in the field or in measuring the actual compaction achieved. Due to the presence of large particles, Laboratory Proctor compaction tests are also difficult to perform on River Shingle or the results are not meaningful. What is the best method to compact River Shingle and how should one measure field compaction?

 

[Ron]

I'm not familiar with the term "River Shingle"....please elaborate.

 

[gortech]

Ron, thanks for your interest. River Shingle is essentially a pit run material typically recovered from the bed of a river or river channel and is comprised mostly of Cobbles, Gravels and Sand with neglegible content of Silt and Clay particles.

 

[Ron]

gortech...kind of what I thought, but wasn't sure.

You might consider getting a scalping screen and running the material across that. It will "scalp" the larger particles so that you get a better distribution.

As for compaction, if the final gradation is not amenable to a laboratory moisture-density relationship, I would simply "proofroll" the material to get uniformity of compaction and not worry too much about the numerical value of that compaction. You can then use conventional materials above it.

One thing you might consider is using a "choker" course of smaller aggregate to fill the larger voids at the surface of the compacted layer, or place a geotextile on it to prevent the overlying structural course from migrating into the voids.