Enlighten Me: DIY Excavation

Foo, had this mostly written up, then was going to edit some more, then Windows rebooted and now here we are... I will try a simpler version! [ED: apparently I can't do simple]

New Garage Time! (Again) Yes I built a garage before, but then we moved. It's okay, the new house is way better, and the new shop will be way better!

Are there obstacles? Yes! Four estimates later, having someone else excavate looks like $30k for excavation, or nearly half the budget for the entire garage. We have a Plan B version of the garage that isn't sunk 4' into the yard, and that takes the amount dug up down from ~350 cubic yards down to ~60 yards.

Assuming DIY, without getting into renting a Bobcat or mini-excavator, Plan A sounds like about $12k to have dirt hauled off in 10-yard dumpsters, Plan B about $2k. Rates for equipment on this scale look to be reasonable if significant. Guessing a couple weeks will also be about $2k.

It's not just the excavation that's coming in higher than expected, so it looks like I'm DIYing a lot again. Roughly leaning toward farming out foundation and framing and DIYing most of the rest.

So, I saw Pheller's thread about DIYing some excavation, and it gave me pause. But I'm not working near a house, I'm not in a huge hurry, and the vast chasm between DIY and Pro costs means I can work awfully slowly and carefully at rental equipment rates and still come out several Miatae ahead.

Before I ask the hive to suggest courses of action, I'll add the observation that the Plan A garage involved excavating a big box for a 30'x34' garage 4' below grade, a parking apron, and a driveway that started there and descended to street level (our yard where the garage will go is about 6' above street level, so the 4' below grade driveway drops another 2ish feet to the street). Plan B basically scrapes about 1' off the yard for leveling, and then has 30" wide, 24" deep footings. The crux of that set of observations is that my naive assumption is that Plan A could've been done with a Bobcat, but Plan B will require a mini-excavator or similar for the footings, and a Bobcat for the scraping. Or if the mini-backhoes weren't roundly panned, that could do both, but it sounds like they're not what they're cracked up to be.

I'm WAY out of my area of expertise, but what looks to me like common sense suggests that I'd need to do the footings first with some excavator-like tool, and I'd need to do that before scraping the main floor area, because the excavator will want to work from a flat surface. Meanwhile, I'll probably knock a bunch of dirt back into the footings while scraping the floor, but at least it'll be loose and hopefully easy to remove.  I'm assuming that scraping the floor first would mean having to work at funny angles with the excavator, and generally suck and/or be beyond the skills of a rank amateur. Or maybe that last  ~1' deep by 30" wide should just be done by hand, since I could do the whole perimeter the first foot with the Bobcat, and even angle out some of the footing... Ugh, that's still over 10 yards of hard dirt by hand. I just unloaded 3.5 yards of soft soil out of the back of the pickup in the last couple of days and that got tedious, though it didn't take all that long.

And now I've rambled past the point where I should've just shut up and waited to see what GRM says.

Qualifications: I worked in excavation for years, as a project manager and operator. 

You're a smart guy, and I guarantee you can do this work yourself. You absolutely definitely don't want to mess with a backhoe, and a skid steer might be helpful; ultimately you need a mini-excavator (also called track-hoe).  An excavator can do the entire job without assistance from another machine, baring any space constraints. I'd suggest somewhere in the 7,000-15,000 pound range. If you have the room to work in, the 14k-18k machines are an excellent sweet spot. Your first few times operating will make you feel like the most uncoordinated lout, but it'll come quickly if you're mechanically inclined. To cut an accurate (by accurate, I mean level and straight) foundation sub-grade, you need to be pretty good. If you're not good on the machine, then just cut as close as you can and tune it up with manual labor. Don't over-excavate: once you disturb those native soils, then you have to either compact the fill you put in or resort to a more expensive import of gravel that can be compacted easily. 

First, the excavation work: cutting down to grade means making a pile of spoil to remove. Plan where you put it so it isn't in the way of further excavation or in the way of loading it out. Cut to grade, set up batter boards so you can layout the foundation with string lines. If you're digging for a footing or foundation walls (as opposed to slab on grade), then you need to excavate WAY MORE ROOM THAN YOU THINK to allow space for placing the forms. Concrete guys will hate you if you cut your trenches tight in order to save yourself some effort in excavation and backfill. You'll need a laser level to shoot your grade and keep everything level. You can do this with clear tubing and water, but that takes forever and I'd really encourage you to spring for the spinning laser level/transit rental. 

Soil removal: If you need soil hauled off site, this is the trickiest part to DIY. You can either hire a dump truck to come and you load them out, but this approach requires a few things: skillful operation and a big enough machine to both reach over the side of the truck and big enough to move a lot of material quickly. If you can find a place locally that will rent you a smaller dump truck like a five yard or something like that, you can manage your own time a little easier. Disposal at most any quarry or landscape materials yard is usually reasonably cheap assuming what you're bringing is clean dirt. Plan to scrape any grass and organics into a separate load. 

60 yards of dirt is still a lot of dirt. If you don't know anyone to do the hauling, you better shy away from DIY with that 250 yard plan. 

Summary: pictures/video walk through of the land and some arm waving of what you want would be really helpful. Please feel free to message me on FB if you want to talk this through. Pretty sure we're "friends" on there. I'm Craig Richmond. 

17 years ago I found out a week before the closing date for selling our house that the septic system failed inspection & needed replaced before we could sell. The replacement cost would have eaten up all of the profit from the sale that we were using for the deposit on the next place, so diy was the only option. 
 

I'd never operated any heavy equipment, but I had a friend who was an operator come over for an afternoon & he showed me how to run the mini-backhoe(I remember him saying the controls were backwards from a full-size one). Unfortunately it broke the next day, so I had to return it & get a mini-excavator instead. It also broke a day or 2 later, but by that point I was backfilling everything in, so I exchanged it for a bobcat. 
 

I can't give you any specific operations instructions because of the years passed since then, but I don't remember any of them being particularly difficult to operate. 
 

However, I had another friend who worked for the USGS that let me borrow some survey gear(and showed me how to use it. That was likely more crucial, as without it I would have struggled to get the correct slope to everything. 

I just got my excavation work finished for my garage.  I would have been done with this job 6 months ago if I could have found an excavator.  I had some show up and bid 21K for the dirt work and slab.  I was like, does that include the building?  Most never bothered to show up and bid.  One started the job, made one huge mess and quit.  Finally found a guy with a 33K lb track hoe and he knocked it out in about 3 days once I got on his schedule.

It's not DIY, but that was getting close if I couldn't get someone to do what I told them.

If you want to do it yourself and you have lots of room, consider renting a bulldozer. That's how it was always done before excavators showed up, and they are very easy to operate. By the time you get down four feet you will be pretty competent and can make the final grade. The trouble with a rookie on an excavator is you will have a lot of trouble making grade which means your footings and possibly slab will require a lot of expensive concrete to fill the holes you made. That or spend weeks filling and compacting. With a cat you can also backfill after and loose some of the excess fill around the yard. Bringing everything up a few inches makes a lot of material disappear. 

Also, four feet for frost protection does not need to be four feet down. You can go down two feet and then bank the backfill to get the frost protection.

Trying to take it all in.

Sounds like you are backing the building into a hill.   If that's so, some of the walls will be holding back dirt  That adds some complexity and expense.  I had the same problem when i built the new shop in 2017.  Instead of hauling away the dirt i dug out for the foundation far enough to be able to walk around the shop, i used that dirt to build a berm uphill from the shop to channel rainwater around the structure and on down the hill.  So i didn't haul any away.   Did the digging my self with a 40hp tractor that had a back hoe and scope on the front.  Only took a few evenings.    Of course I have a bit of land to work with.   YMMV

Was responding and the website crashed and made me start over. Short answer is yes you can do it yourself. I did similar on a .18 acre site next to an existing building for my 450 sf addition. The project had 30” deep footings on 2 sides, 16” deep turn downs on the rest, and some interior column footings.

a bobcat is good for moving dirt and debris quickly from one location to another, but the mini excavator can do everything in a pinch. If you have the ability to put your spoils and haul off vessel close to the site skip the bobcat. If you have to move a long way between any of these items the bobcat will save lots of time.

i will say be careful about doing a shallow slab excavation. Topsoil is great for growing stuff but doesn’t compact well. I ended up having to go 18 to 24” down and build back up with stone. Worth it but will cost you haul off and stone cost.

Take a good look around your neighborhood and find the guy with the low spot that could be turned into something if only he had 30 truckloads of dirt. Win-win.

See also swimming pool. 

Listen to EVERYTHING Mezz just said. 20 years of dirt work, and everything he said is 100% accurate. Also, have formed and poured foundations and walls. Concrete guys with room to move and set up will give you a better finished product. Don't crowd them.

In reply to Appleseed :

I have almost thirty, for what it is worth.

I built a garage at my first house, and the concrete guys didn't use forms for the foundation, only 2x4 forms for the slab where it stuck up above grade. My brother did the excavation for me, just dug the footer and foundation trenches using a 12" bucket and the concrete guys did a "monolithic pour" where the footer and foundation were a single pour of reinforced concrete. Is that not an option here?

oldopelguy said:

Take a good look around your neighborhood and find the guy with the low spot that could be turned into something if only he had 30 truckloads of dirt. Win-win.

See also swimming pool. 

Speaking as someone with a low spot like that, I think this idea has a lot of merit. If your neighborhood has a facebk group, that could be a great place to ask of anyone needs your dirt.

The other thing that needs amplification (Mezz touched on it but didn't mention this point): 

DO NOT bottom out your foundation trench until you are ready to pour the footings very very promptly afterwards.  Even if you manage to get a nice, neat, level floor to the excavation, a couple days of strong rain can muck that up so that you have to dig another foot or more down to get soil solid enough to build on (or backfill with expensive compacted gravel).

Mezzanine I like your nickname?

Thanks very much, all!

To clear up some confusion in the above stuff, mostly my own fault for not just talking about Plan B, which is actually the only sane plan:

• We'll be about a foot deep. The 4' deep version went out the window along with its additional 300 yards of removal, and I shouldn't have mentioned it, no matter how cool it was.
• It's technically on a slope, but it's not anywhere near a foot difference from the front to back of the shop. Most of the rest of the... 3'-4' drop is from the shop to the street.

Our new spammer does point out an amusing coincidence; the new garage will have... A mezzanine!

er, about a 10' deep section at the back where it'll have an upstairs where I can store stuff, with stairs running up. The prior garage taught me that while ladder access is better than no storage, there are serious limits to what I want to carry up a ladder, and I hope I get to use this garage 'til I'm old enough to be even more disinclined.

But I digress. No actual hand-waving, but here's a quick walk around the yard in the vicinity of the shop and driveway. I need to work on my narration skills.

Here's what it all looks like from above. The yard steps up right at the front yard side of the sidewalk about 2', then slopes upward to the back so gradually you'd think it was flat, excepting a step a bit less than a foot where those hedges shown in the video split the front and back halves of the yard (right between the cars in the image below).

...so the driveway will probably need to lose... 3' ish on the way to the street. I could be significantly wrong there. I think it might be less, but we won't know for sure 'til I have spinning lasers of precision.

In good news, yesterday the road to the place where I'll be dropping the dirt was open. It could just be a weekend/coronavirus thing and it'll go back to being one way only, but that makes it a 5 minute drive from the house instead of 15. That will help with getting rid  of 50 yards 5 yards at a time more quickly. Which is my current guess about pulling up 60 yards and putting 10 yards into the grassy knoll/water feature we want in the opposite rear corner from the shop. It is not a JFK conspiracy shrine, we just want a little hill with a little stream.

At the amount of dirt we're talking about, it's sounding like the 5-yard dump truck and dumpsters are a wash for cost, but the ability to just keep loading and running down there on my own schedule makes the truck the win, I'm pretty sure. As opposed to having to wait for dumpsters to be swapped every ten yards.

How does one determine whether the existing dirt is solid enough vs needing to dig deeper and get crushed gravel? We have high-clay soil that generally needs regular aeration not to kill all the grass and turn into a giant brick. It's very, very, very important to me that my garage floor does not become the mountainous aberration which the old garage has. My welding table's front and rear feet are probably set more than an inch different to get to level.

Anyone want to hazard a guess at how long a job this excavation is for a slow operator? A week? Two? Bracing for the rental...

Mezzanine, thanks again for spelling out the basic "stick the dirt where it won't get in your way while you do the job, and where you can get to it to put it in a truck when you're done." There are some "obvious" basics I didn't have in mind. When I was thinking dumpsters, I was imagining excavating directly into said dumpsters, which would be slow going, even if I had each successive one placed close to where I was working at the time.

How much room is a lot of room for the concrete folks? I want to make them so freaking happy that they make me a foundation worthy of being the first layer of my workbench for many years to come, and  backfill I don't even have to pay to dump, so it's just digging time.

Lots of good accurate info here.   Let me add:

- All excavators (no matter how big or mini) take practice to cut a level trench. The problem is the pivot (elbow joint) of the excavator arm makes the bucket cut in an arc. You can't cut level by just drawing the bucket toward you. You have to also lift the arm at the same time in the center of the arc, then lower it back down as the bucket gets closer to you. It takes 2 hands, and practice. 
 

The arc of the arm is more than a foot. If you don't adjust the arm elevation at the same time you are pulling toward you, you will dig a scalloped bottom trench, with the deepest parts being more than a foot too deep. 
 

Why does it matter?  Because you CAN'T fill if you dig too far. Loose fill is hard to compact again, and inadequate to support a building foundation. 
 

Yes, a DIYer can learn to do this. I wish you had 20 acres to practice on. 

Here's my suggestion (especially as an amateur)...

Set up the batter boards on top of the existing grade. Layout the footings, and dig ONLY the footing trenches (not the center excavation).  Have at least 2 extra people available, and rent a good rotating laser level. 1 guy in the trench checking grade continuously, 1 guy cleaning the trench with a shovel.  Go slowly, and follow that laser as close as possible. Dig an inch or 2 less than needed, and finish by hand. Throw your spoils (waste) INTO the center of the garage.

Then pour your concrete footings. In the trenches. Use the trench walls as forms- no formwork.  You should have 6-8 strong friends to help pour.
 

After the footings are complete, dig out the rest of the excavation (being careful not to damage your footings).  Include clearing enough space outside the footings for the masons/ form guys to build the walls. 
 

You will be able to establish your subgrade by pulling a string from footing to footing while you excavate.

Give yourself 3 days to dig footings, 1 to pour, and 3 more to excavate out the center.

(A pro could do each in a day)

Don't try to pour your own floor.  That's a job for a pro. But there is no reason you can't pour your own footings if you do it this way.

One other note...

Your foundation crew will not be so freaking happy with your work. You are not a pro. Be honest with them, and accept it.

Its ok. They can fix it.

SVreX said:

I wish you had 20 acres to practice on. 

Me too. Thanks for the tips!

I guess it'll become more obvious as I practice, but I guess I'll just have to see what my tolerances look like as I get there, and if I can't keep them tight enough, I'll have to finish by hand. Which would suck, but not as much as having the garage settle a bunch.

I wonder how far they are from fly by wire excavators allowing a "straight pull" lever that automates mixing elbow and lift to make a straight line.

Oh! Guessing I can trade efficiency for caution by scooping from near the bottom of travel back toward me, so I only get the upward part of the scallop? I don't want to surrender before I start, but an excavator at 1/3 speed is still faster and easier than a shovel...

Pretty sure you will have to have architectural plans to build in Portland.  These will determine footing thicknesses, depth, etc.

But your frost line in Portland is 18".  That means anything you dig will HAVE to be a MINIMUM of 2' deep. The low side of your excavation will be that deep- as the grade rises, your footings will be deeper (and will step up)

SVreX said:

One other note...

Your foundation crew will not be so freaking happy with your work. You are not a pro. Be honest with them, and accept it.

Its ok. They can fix it.

I can live with that. I'm DIYing what I can, and I'm happy to pay pros for the stuff I need to have them do, including the extra work I create.