During the raw development phase, your project will either be an “EXPORT” or an “IMPORT” site in regards to dirt. (Or a “BALANCED” site.) And having a balanced site may arguably be a preferred option due to not needing to import or export any dirt from the site. However, there are some BIG BENEFITS you can take advantage of if you have an IMPORT site!
Before I continue, allow me to first briefly explain a “balanced” site. A balanced site means that you will not need to import or export any dirt. Or in other words, the amount of “cut” needed in your jobsite will equal the amount of the total “fill”. (If you don’t know what these terms mean, then head over to the Rough Grading Introduction post and learn them over there!) All the dirt you need for your grading is already on-site. Sounds great, right? Well, while this may be an advantageous condition, it may not be the MOST preferred with all builders! WHY?? Because you can’t leave a DISPOSAL HOLE!
WHAT IS A DISPOSAL HOLE?
A disposal hole is exactly what it sounds like. It’s a very large hole in your site in which you can dispose of dirt throughout the development process. Now let me once again emphasize the fact that almost ALL of your construction operations WILL GENERATE DIRT! (Also known as SPOILS.)
And one of the BIGGEST areas within your site that will consistently generate spoils throughout the life of your project is your PRODUCTION SPOILS (or the development of each house lot). If you recall from the “Finish Grading Introduction” post, it’s your finish grader who will handle these spoils. And if you can pay your finish grader to haul these dirt spoils ON-SITE rather than to an OFF-SITE location, then this could cut your costs significantly! (Possibly anywhere from $1,500 to $700 per lot! Almost half! Multiply that savings over 20, 30, or even 100 lots and see how much your overall total savings would be!)
So if you have a perfectly balanced site, you will have nowhere for your finish grader to haul his dirt to onsite. But with an import job, you can simply direct your rough grader to import less dirt than what is needed, thus leaving yourself a disposal hole! (Hint: This is ALSO an added cost savings because you won’t be paying for as much import).
HOW MUCH DIRT CAN MY DISPOSAL HOLE TAKE?
As you might recall from the “Rough Grading Introduction” post, in order to find out the size of your disposal hole you would request a “CUT / FILL MAP” from your engineer (or your rough grader). Your engineer would then take a bunch of shots of the hole in order to find the elevations of the existing topography and overlay that with the finish design grade elevations. And what your left with is a bunch of areas where you would either have to cut dirt or fill in dirt to reach that design grade.
Your “CUT / FILL MAP” will then summarize the total “cut” and the total “fill”. In the case of having a disposal hole, you would be left with a TOTAL NET “FILL” in cubic yards (CY), which is your total capacity for your disposal hole!
HOW LONG WILL MY DISPOSAL HOLE LAST?
In order to figure this out, find out from your finish grader how much dirt they can anticipate to pull for each lot. For our examples in this post, let’s estimate 150 cubic yards of spoils per lot. BUT BE CAREFUL, just because you may have the capability to leave a disposal hole large enough to take in ALL of the dirt spoils for EVERY lot, it’s not a wise move. That’s because your disposal hole location will most likely also be in the same vicinity where the future houses will be built. And you won’t be able to build those homes if that hole isn’t 100% filled in! (You can’t build your houses in a hole!)
EXAMPLE 1
Q: You have an import job of 45 lots with a disposal hole of 2,500 CY. How many lots will it be able to accommodate?
Solution: 2,500 CY (disposal hole capacity) / 150 CY (production spoils for one lot as mentioned above) = 16.67 lots. So 16 lots total. The spoils for the remaining 29 lots will have to be hauled off-site.
EXAMPLE 2
Q: You have an import job of 30 lots with a disposal hole of 6,000 CY. How many lots will it be able to accommodate?
Solution: 6,000 CY / 150 CY = 40 lots. HOWEVER, THIS IS A TRICK QUESTION!! This is more lots than you have for this project! So the REAL question is: how low do you leave the disposal hole?
The REAL Solution: To figure this out, notice that the surface area of the disposal hole covers 8 lots. So that means that the hole should ONLY accommodate just 22 lots (30 lots – 8 lots = 22 lots) in order for it to be filled completely by the time the final houses are built on top of it. Therefore, the hole should be left low to fill just 3,300 CY (22 lots x 150 CY = 3,300 CY). You will then have to import the remaining 2,700 CY of dirt (6,000 CY – 3,300 CY = 2,700 CY) in order to fill the hole 100%.
