NCMA SRW spec question.

[forestfireguy]

Let me start off by saying I've been meaning to go to the NCMA class for a couple years now. My boss is certified but forgot the answer to this question. When backfilling a SRW what do you use, 3/4 crushed or 3/4 (clean) crushed washed ? I ordered washed for our stock for use as backfill, thinking that not having the fines present was the whole idea behind using stone and fabric when backfilling. Anyone know for sure?

[Captains Landscape]

3/4" crushed angular is fine. I was told by an engeneer that the fines will just blow through the stone. In this particular case it was better to use no geotex to separate the stone from the retained soil because there were so many fines in the soil, the geotex would clog (putting hydraulic pressure on the wall). It was better to let the fines wash through the face of the wall.

I'm not suggesting you do this on your wall...just giving an example

[Grn Mtn]

page 9 of my NCMA installation manual states that: "...The drainage aggregate shall be a clean 1 inch (25.4mm) minus crushed stone or granular fill meeting the following gradation.

Sieve Size / Percent Passing

1 inch --------------------100
3/4inch ------------------- 75-100
No.4 ---------------------- 0-60
No.40 -------------------- 0-50
No.200 -------------------0-5"

[Captains Landscape]

correct me if I'm wrong but where I get my aggregate, 3/4'' meets that gradation. A clean one inch MINUS is not the term my suppliers like to use, but according to the gradation report given to me 3/4" washed is what I should use.

[cgland]

correct me if I'm wrong but where I get my aggregate, 3/4'' meets that gradation. A clean one inch MINUS is not the term my suppliers like to use, but according to the gradation report given to me 3/4" washed is what I should use.


You are correct. Your drainage zone should always be a "clean" stone. Your infill material can be modified, but....$$$$$$$$

Chris