Gravel under outdoor concrete flume?
Gravel under outdoor concrete flume?
(OP)
Hi,
I have a follow-up question about a flume I am designing to carry stormwater outside. It is to be of reinforced concrete in a U-shape, with #3 bars in a single mat through the U-shape, with the bars both horizontally and vertically. The depth is to be only about 1.42 ft (1 ft 5 inches) including the floor depth. The walls and floor are to be fairly thin (due to site constraints), at 0.42 ft (5 inches). The flume is to be dug into previously placed fill material outside a house with a fairly deep foundation. Should there be something like 4" depth of gravel underneath the concrete? The job site is not in an area subject to freeze-thaw conditions (a far southern state). If needed, what size of gravel is recommended? What is the purpose of such gravel? And, lastly, in the area of the project, "flexible base" is often used for roadway base material. Could such be used under the flume? Gradation requirements for flexible base are as follow: 1-3/4" 0% retained; 7/8" 10%-35% retained; 3/8" 35%-50% retained; #4 sieve 45%-65% retained; #40 sieve 70% - 85% retained. Or, would it be recommended to just forget about the potential use of flexible base, and just call out for 3/4" gravel under the flume (if it is needed at all).
Thanks!
I have a follow-up question about a flume I am designing to carry stormwater outside. It is to be of reinforced concrete in a U-shape, with #3 bars in a single mat through the U-shape, with the bars both horizontally and vertically. The depth is to be only about 1.42 ft (1 ft 5 inches) including the floor depth. The walls and floor are to be fairly thin (due to site constraints), at 0.42 ft (5 inches). The flume is to be dug into previously placed fill material outside a house with a fairly deep foundation. Should there be something like 4" depth of gravel underneath the concrete? The job site is not in an area subject to freeze-thaw conditions (a far southern state). If needed, what size of gravel is recommended? What is the purpose of such gravel? And, lastly, in the area of the project, "flexible base" is often used for roadway base material. Could such be used under the flume? Gradation requirements for flexible base are as follow: 1-3/4" 0% retained; 7/8" 10%-35% retained; 3/8" 35%-50% retained; #4 sieve 45%-65% retained; #40 sieve 70% - 85% retained. Or, would it be recommended to just forget about the potential use of flexible base, and just call out for 3/4" gravel under the flume (if it is needed at all).
Thanks!





RE: Gravel under outdoor concrete flume?
RE: Gravel under outdoor concrete flume?
Dik
RE: Gravel under outdoor concrete flume?
RE: Gravel under outdoor concrete flume?
I am not sure what size "A" base is, and I searched online and nothing came up. From what grading/rating system does such base sizing come?
Thanks.
RE: Gravel under outdoor concrete flume?
https://www.google.com/search?q=aggregate+base+cou...
RE: Gravel under outdoor concrete flume?
RE: Gravel under outdoor concrete flume?
CRUSHED ROCK COMPOSED OF HARD DURABLE UNCOATED FRACTURED FRAGMENTS PRODUCED FROM ROCK FORMATIONS OR BOULDERS OF UNIFORM QUALITY, OR A MIXTURE OF CRUSHED GRAVEL, SAND AND FINES COMPOSED FROM NATURALLY FORMED DEPOSITS ONFORMING TO THE PROVINCE OF MANITOBA SPECIFICATIONS FOR AGGREGATE FOR GRANULAR BASE COURSE FOR CLASS A
FILL SHALL CONFORM TO:
SIEVE SIZE (ASTM) PERCENT PASSING
3/4 INCH 100
5/8 INCH 80-100
NO 4 40-70
NO 10 25-55
NO 40 15-30
NO 200 8-15
It's a common gradation here and elsewhere...
Dik
RE: Gravel under outdoor concrete flume?
SIEVE SIZE (ASTM) PERCENT PASSING
1.75 INCH- 100% passing (compared to no callout for Granular A)
7/8 INCH- 65-90% passing (compared to no callout for Granular A)
3/4 INCH- not specified (compared to 100% passing for Granular A)
5/8 INCH- not specified (compared to 80-100% passing for Granular A)
3/8 INCH- 50-65% passing (compared to no callout for Granular A)
NO 4 35-55% passing (compared to 40-70% passing for Granular A)
NO 10- not specified (compared to 25-55% passing for Granular A)
NO 40 15-30% passing (equal to 15-30% passing for Granular A)
NO 200- not specified (compared to 8-15% passing for Granular A)
Until I hear back from the gravel/stone supplier, do you have any thoughts about the suitability of the above shown "flexible base" for the base below the flume, in comparison to the suitability of the Granular A?
Thanks!
RE: Gravel under outdoor concrete flume?
RE: Gravel under outdoor concrete flume?
RE: Gravel under outdoor concrete flume?
Dik
RE: Gravel under outdoor concrete flume?
Thanks.
RE: Gravel under outdoor concrete flume?
local spec here is:
sieve % passing
1-1/2" 100
1" 90 - 100
no. 4 38 - 65
no. 8 25 - 60
no. 30 10 - 40
no. 200 3 - 12
PI 5 max
RE: Gravel under outdoor concrete flume?
RE: Gravel under outdoor concrete flume?
in order to get good compaction and a smooth working surface with largeer rock you need two things: 1) a thicker lift (thicker than 4 inches as you suggested) and 2) heavier compaction equipment. For a small trench, thin lift and light compaction, stick with smaller size aggregate.
RE: Gravel under outdoor concrete flume?