# Formulas

Discussion in 'Landscape Architecture and Design' started by kris, Feb 4, 2005.

1. ### krisLawnSite Bronze Memberfrom nowherePosts: 1,578

It Would Be Great if others could join in with any formulas they might have that are used in construction.

the term gradient means the fall or rise of land per horizontal unit and is usually expressed in percentage.

The one essential mathematical formula for most grading challenges is used to compute gradients.

The formula will allow you to figure out..

* the percentage of slope between two know points and a given distance

* the horizontal distance between points when the gradient and vertical elevations are known.

* the vertical elevation between points when the gradient and distance are known.

G= D divided by L
or
L= D divided by G
or
D= G x L

D=the distance in elevation between two points
L= the horizontal length between two points

2. ### krisLawnSite Bronze Memberfrom nowherePosts: 1,578

Well this thread went over big! LOL :blush:

3. ### D FelixLawnSite Bronze Memberfrom Putnam County, IndianaPosts: 1,898

I just can't think of any right now.

The 3,4,5 triangle that was mentioned in another thread is a way to get a right angle. The 5 is the long side of the triangle, the 3 and 4 are the other two sides. Any multiples of those numbers will work. Doesn't matter whether it's feet, inches or even meters for those of you that measure wrong. Measure down one side 3 feet, the other side 4 feet, then move them so the two marks are 5 feet apart. Viola, you have a right angle. Probably not the best explanation in the world.

A cubic yard of mulch will cover ~100 square feet at 3" thick (for quick estimating purposes).

Your formulas for gradient is fine, but what I don't understand is why a ratio for a slope is given the way it is. When you hear an excavator say a 2:1 or a 5:1 slope means that it has 2 feet or 5 feet of run, to 1 foot of hieght. That is backwards to how slope was taught in high school math class, it was always "rise over run", or 1/2 or 1/5. Anyone have any insight as to why the ratio is given backwards?

I'm sure there's other formulas, etc. that I use, I'll think of this thread the next time I use them.

Dan

4. ### krisLawnSite Bronze Memberfrom nowherePosts: 1,578

I don't have a solid answer for you Dan .... I'll just think out Loud.

I wonder if it has something to do with contours? You know ..its the way you would draw it?
or
maybe it has something to do with expressing it as an angle which I never do because it is difficult ... need a protractor or converted from reading tables.

Really ..I'm guessing.

Your point is a good one and it is worth noting the the ratio is expressed by some with the rise first ...all I can say is if the ratio seems excessive, check to see if it is backwards.

5. ### MarcusLndscpLawnSite Senior Memberfrom New EnglandPosts: 634

Hey guys. Dan is correct....it takes a little thought to come up with these formulas when the project or problem is not right in front of you. One I did come up with is a general rule of thumb when it comes to building stairs.
It should be noted that every situation is different and the following formula can be tweaked to fit your project. With that said, generally, 2 Risers plus one tread should equal 25-27 inches. So, 2R + T = 25-27 inches.

So if you have a 7" riser your tread should be 11-13"
so on and so on

6. ### D FelixLawnSite Bronze Memberfrom Putnam County, IndianaPosts: 1,898

I knew of that formula, and actually thought about it while I was typing my first post, but couldn't remember exactly how it went. Thanks ML!

I'm curious to see if anyone knows why slopes are expressed differently....

Dan

7. ### YardProLawnSite Gold Memberfrom coastal NCPosts: 3,567

e=mcsq.............

lol
that one comes in really handy at work

i have some at my shop that i don't use often like
figuring the volume of a pile by it's dimensions, etc.

also when excavating dirt expands 25% (i think that's the fugure)

to figure the volume needed to make a rounded berm

V=pi(r)squared(legnth) r being 1/2 the width

8. ### D FelixLawnSite Bronze Memberfrom Putnam County, IndianaPosts: 1,898

Nope that's the fIgure.

If you dug a 3' square hole, 3' deep (one cubic yard), that yard "in the ground" would be ~1.25 yards in a pile, depending on soil types. Put that yard back into the hole, compacting as you go, and you will then have ~.95-.97 yards, again, depending on soil type.

Dan

9. ### krisLawnSite Bronze Memberfrom nowherePosts: 1,578

Ya that extra 25% "fluff" rate gets overlooked quite a bit I bet ... need it when your figureing your trucking hours ect.

how to figure cubic ft in a cone ... volume = 1/3 (area base x height) .. can't say I use that much

area and circumference of circles is one I have to use alot in calculating mulch and edging material in tree rings.

circle area.... A = pie r2 pie being 3.14
circle circumference= 2 pie r

10. ### mbellaLawnSite Bronze Memberfrom Gilbertsville, PAPosts: 1,284

Here's a sports formula: E A G L E S= SUPER BOWL CHAMPION. Had to add that. I'll post something serious next week. Good thread Kris.