If you’ve been around construction, you MUST know that extra dirt just always seems to generate! It seems as if any time a John Deere or CAT equipment touches the ground, dirt spoils just appear! This happens for almost every trade in land development. From pipeline installation, retaining wall footings, planting trees, and more. And if you’re not prepared for it, you’ll be spending more and more money to continuously haul that dirt off your project. So, here are a few tips that can help you anticipate these spoils. And better yet, prepare a place to lose more dirt ON SITE!
Firstly, one of the common areas to lose more dirt is, well as a matter of fact, the COMMON AREAS! Typically, your finish grader will be doing some fine grading here prior to the softscape and hardscape (even though it’s already been rough graded at the beginning of the project). Since that’s the case, just have your finish grader spread that dirt around at the same time.
EXAMPLE 1 – Lose Dirt in Common Areas
As an example, for one project we had quite a bit of trenching for the off-site electrical conduit. The trench was 2 ft wide x 4.5 ft deep (2 ft x 4.5 ft = 9 sq ft).
Now, most of the dirt would be used as backfill in the same trench, but not all. We estimated about half would be left over, due to bulking as well as other conduits that might get thrown in there (9 sq ft / 2 = 4.5 sq ft). And the total length of this new line was about 1,289 ft, thus totaling about 5,801 cubic feet of extra dirt spoils (4.5 sq ft x 1,289 ft = 5,801 cu ft).
And the size of the common area within this project was 39,029 sq ft. Obviously, we did not have a depth yet, but we knew that we wanted it to accommodate 5,801 cu ft of spoils. So, we can write this equation as:
39,029 sq ft x (unknown depth) ft = 5,801 cu ft
Or, in order to isolate the unknown variable, we can write it as:
5,801 cu ft / 39,029 sq ft = (unknown depth) ft
Now after solving for the unknown, we get a desired depth of about 0.14 ft (or 1 ¾”). So theoretically, if the grader leaves the common area low by about 1 ¾”, then it can accommodate most of the off-site dry utility trench spoils.
However, you must keep in mind that the finish grade might also need to be left low for the landscaper. The landscaper may have to place mulch, woodchips, or some sort of other softscape fill. So, if the landscaper needs about an inch for mulch, then you will have to leave it 2 ¾” low (1 ¾” + 1”).
DON’T FORGET ABOUT TREES!
For an added bonus, you can also figure the spoils from the planting of new trees! For instance, for a 24” boxed tree you can figure about 6 cubic yards of dirt to be removed. So, depending on how many trees you have, you can account for this dirt in your common areas and lose more dirt here as well!
EXAMPLE 2 – Lose Dirt in Streets
If your new development calls for a large storm drain, then that, too, will also produce a lot of dirt. And one trick you can do to lose your storm drain dirt spoils is to keep the street section low (the “gut section”).
In this scenario, for a 24-in diameter storm drain, we estimated that about 10 sq ft of dirt would be left over for every lineal foot. The storm drain run was about 1,144 ft, which calculated out to be about 11,440 cu ft of dirt spoils (10 sq ft x 1,144 ft = 11,440 cu ft).
Now let’s figure out the total square footage of the street. Per the detail below, the street width (from curb face to curb face) is 36 ft wide. However, you need to leave 3 ft of bench on either side for the curb & gutter machine. So, we’re actually looking at a width of 30 ft.
(Keep in mind, in this situation we only have the LENGTH and WIDTH of the street. The DEPTH is the unknown variable we will be looking for.)
The total run of street we had in this scenario is about 900 ft. Thus, giving us a square footage of 27,000 sq ft (30 ft x 900 ft = 27,000 sq ft).
Now, using the same equation used in example 1, we can solve for the total depth:
27,000 sq ft x (unknown depth) ft = 11,440 cu ft
Or, we can rewrite it as:
11,440 cu ft / 27,000 sq ft = (unknown depth) ft
Once again, solving for the unknown variable will give us a total depth of about 0.42 ft (or 5”). So, in conclusion, if the grader leaves the street gut section low by about 5”, it would be enough to take all the dirt spoils from the storm drain pipe installation.
CONCLUSION
You might be asking yourself, “why does it matter? If the rough grader has to remove that dirt at the beginning in order to accommodate those spoils down the road, then isn’t it just the same thing if the finish grader were to haul it off later? Either way, won’t someone have to remove the extra spoils no matter what?”.
Well, technically you are correct. HOWEVER, the rough grader is meant to move lots of dirt. The rough grader typically has bigger pieces of equipment, so they can move a lot more dirt at a time (therefore, it’s cheaper). Whereas the finish grader is really built to move smaller amounts (hence the term “fine grading”). The finish grader does not typically usually as big of equipment as the rough grader. It’ll most likely be cheaper to have a rough grader move (and possibly haul out) some extra dirt than to pay a fine grader later on to bring some trucks in to load and haul out. In conclusion, think ahead and plan for future dirt spoils that will come up. Remember, dirt spoils just seem to grow in a construction site. And it can very well become a nuisance if you don’t plan for it. So, have the foresight to
