A little math help please?

[P Dubya]

I'm trying to figure out about how much rock I would need to bed a 24'' pipe in a ditch 30 inches wide and 100 feet long.... I need to have 5 inches of rock under the pipe and rock up the walls of the ditch to the top of the pipe. Just enough to leave the very top visible for inspection.... I figure the bottom 5'' of rock would add up to about 5 cubic yards over the width and distance of the ditch but I'm stumped on how to figure the rest.... Any ideas or formulas? Thanks!!

 

[raddksn]

I'm thinking after inspection you need to cover over the top?
Just figure that pipe as a 24" square 100' long that would be pretty darn close!

 

[wnstwolf]

235 cubic yards (I used 30" deep so you can cover pipe after inspector leaves) for #5 stone looking at 40ton or so?

 

[Trucksold]

I calculated 10 3/4 yards. To get this I found out how much rock it would take to fill a 30" wide by 29" deep ditch and then subtracted the volume of the pipe. The 29" depth would be 5" below the pipe plus the 24" pipe. If your wanted a little bit more of the pipe exposed, you could calculate it at a little less than 29".

 

[Rookie2]

I get 10.75 also but what trench is exactly 30" wide so figure on several extra yards, you pay for trucking one time.

 

[P Dubya]

raddksn... No more rock needs to go in after inspection. I only have to be able to show inspector that the joints on each pipe are fully seated.

wnstwolf... How did you come to that figure? Not questioning whether it is right or wrong just want to know how you arrived at it? 235 cubic yards of 1'' roadstone (Not sure what the #5 stone is where you are) would weigh in at about 36 tons....

 

[P Dubya]

Two more replies while I was typing my last reply....

Trucksold.... That makes perfect sense the way you explained it, how did you figure the volume of the pipe? Is that one of those Pi/R/squared things I forgot long ago?

Rookie.... I fully agree on the trucking. A few extra tons of rock would be cheap insurance....

 

[DenisG]

For simplicity, make the trench 30" wide by 30" deep or 2.5ft x 2.5ft.
The volume of this empty trench 100ft long = 2.5 x 2.5 x100 = 625 cu ft.

The volume of 100 ft of 2 ft diameter pipe is pi * r^2 x 100 = 314 cu ft.

When you put the pipe in the trench, that's less stone that you have to put in. 625 - 314 = 311 cu ft. You'll need 311 cu ft of stone or since 27 cu ft = 1 cu yd, 311/27= 11.5 cubic yards. Round up to 12 yards to be safe.

 

[Jim in Wis]

The area of a circle is pi * radius squared - volume is area times length
3.14 times 1 squared is 3.14
3.14 times 100 is 314 cubic feet for the pipe
volume for the ditch is height times width times length
2.5 times 2.5 times 100 is 625 cubic feet
625 cubic feet minus 314 cubic feet is 311
there are 9 cubic feet in a cubic yard
311 divided by 9 is 34.5 cubic yards
at least that's how it looks to me

oops you guys are right, 27 cubic feet in a yard, not 9
11 or 12 yards is right

 

[ahab]

30 inch wide ditch filled 24 inches deep - area displaced by 24 inch pipe) = (30*24)-pi24^2 = volume of rock for 1 inch

volume of rock for 1 inch * length of pipe (in inches) = total volume

then convert to whatever units the rock company wants.

 

[Trucksold]

P Dubya

DenisG has it almost right on the volume of the pipe. Its actually the radius instead of the diameter squared. He used the radius when he made his calculation, but wrote diameter instead.

 

[Angelfire]

Jim, there are 27cf in a cy, not 9. Otherwise, your math is correct.

 

[P Dubya]

Jim in Wis... I agree up to the 9 cubic feet in a cubic yard point.... 3x3x3 is 27... 27 cubic feet in a cubic yard. Looks like the 12-15 yard point is where I want to be on this project.

 

[DenisG]

P Dubya

DenisG has it almost right on the volume of the pipe. Its actually the radius instead of the diameter squared. He used the radius when he made his calculation, but wrote diameter instead.

You're right, I corrected myself. Transcription error from my scratch note!

 

[Always_Thinkin]

If your 1" roadstone has fines in it like I am thinking there are two conversions you use to get your cubic yards into tons of rock. In Illinois/ Missouri where I live (limestone product) a "compacted" road stone would yield 1.5 tons per cubic yard and "loose or dumped" road stone would yield 1.3 tons per cubic yard. When you order the rock they will ask how many tons you need so this should help.

 

[Strouty]

235 cubic yards (I used 30" deep so you can cover pipe after inspector leaves) for #5 stone looking at 40ton or so?

Do you realize how much stone that is?

 

[rlitman]

235 cubic yards (I used 30" deep so you can cover pipe after inspector leaves) for #5 stone looking at 40ton or so?

I didn't do the math, but your number looks like it is in cubic feet, not yards.

 

[nehog]

312 cu ft.

 

[tomroblee]

I'm just curious. What kind of pipe are you bedding in rock??? I always thought that pipes were generally bedded in sand to protect them from rocks.

 

[LS6 Tommy]

1+1= 2?

Tommy

 

[lynnbilodeau]

I was told there would be no math.

 

[P Dubya]

tomroblee... It is a 24'' storm sewer. Dual wall plastic HDPE gasketed pipe.

 

[wnstwolf]

woops.. yeah failed to account for that huge thing in the middle of the hole! doofuss Rlitman spot on cubic ft..

dumbazzz I will stick to reading the pots. ;-)

 

[Brad Beam]

11.37cy