grading my yard for garage slab w bobcat 743. cohesive rich black dirt, some mixed w gravel. I spread broken conc chunks in low areas, covered with 6" soil and drove over multiple times till looked tight. Will that be enough compaction under another 2 to 6 " of crusher run for a sub base for 4" conc slab?
Put a lot of water on it.
pick up a full bucket for the best effect. I would rent a plate compactor when it was all done and run a plate over it for my garage. It is ~$100 for 4 hours of peace of mind.
10 4
run the plate before and also after the crusher run?
up to you. if the total depth of the fill is less than 1' then the top pass is enough, if you rolled that in. That is how I figure the half day rental if you can get it. Have it all done and then plate. The Chef's kiss.
A thousand pounder can give you a lot of compaction.
So now I'm thinking about raising the slab a bit. If I have 1.5' of fill at the low point would I want to use a larger rock first then 6" of ab3 on top? or would 3 lifts of 6" ea. be fine? I'm also debating on whether to run a wall around the perimeter and just fill the inside or overfill the footprint a couple feet and slope down then it's just a slab on grade with thickened edge.
You’d have to compact those 3 lifts, be more feasible to put some 1 1/2” crusher run in low spots and mini pack over that and water and compact over that. That would insure good drainage if lifted a bit. Are you doing an Alaskan slab?
I sometimes build smaller pads like you are describing with just my Case 1845C skid steer. I compact in 6" lifts with a bucket full of dirt for extra weight. As long as the dirt is good and proper moisture I can pack tight enough you could drive a fully loaded cement truck over it and not leave a mark. However, I would still only build a monolithic (Alaskan style) slab on these pads and use plenty of rebar. If it was a structure of any great size or weight I dig footers on virgin ground, block up to finished height (often a stepped footer), back fill the inside with clean #57 gravel, and pour on top of that. Outside would be back filled with dirt.
Welcome to the Forums MR13! Do you have any pics of the site? Not familiar with "cohesive rich black dirt" in your area but here dirt of that description wouldn't be used for structural fill. Yes a 743 wheeled BC can achieve compaction as compaction is a ratio of weight, manipulation, lift thickness and time. Time being the biggest factor. Not familiar with an "Alaskan Slab". Is that a turned down footing monolithic slab? If so very common here.
thank you to everyone who has responded. I will take some pics tomorrow and post. I just called it cohesive because it packs together really solid and Rich black because it's very dark and it's not clay. I don't know how far down I would need to over dig to get to Clay which is down there somewhere.
Rich and black means a lot of things to a lot of people, no judgement, but that's not what I want for a stable base. How about a jar test of the soil, post pics of the results.
You want clay not some form of black dirt.
What's the tire pressure on the skid steer tires?
Yes I'm doing monolithic with turn down edge, also first I've heard the Alaskan name. here are some pics of the dirt don't know if they're clear enough to show anything but I think I'd have to dig out a couple feet to get down to clay.
That’s a nice base. Yes a monolithic was called an Alaskan slab for about 40 years before some engineers came up with monolithic. Lol My garage has 16” edges with a 6” floor and rebar, no wire. Lotta people now believe wire is bad, myself included.
70, 40, 40, 30 lol... new machine to me I guess I need to check my pressures once in awhile ha.
okay I'm starting the jar test now first mark is the sand, in two hours I'll check the silt, then two days the clay
Hard to tell but from the pics but it looks like the "black dirt" has a lot of organics in it which is something you don't want under a slab. You want to remove any material that has organic material in it under the slab. How expensive is crushed stone in your area? Do you have a place on your property to waste the undercut? Interesting. Minimum code here is 18" on a turn down. 12" for our "frost line" which is laughable since it never freezes and 6" from finished dirt grade to finish floor.
Our frontline here is 3 feet but a monolithic save 10 to 15 grand minimum to get below the frostline with a wall.
I don’t see any organics in that dirt but maybe I’m wrong. Looks super tight for what it is. To me, it looks like a great dirt. After a 3rd look I see some vegetation, not sure how long it been like that, if it’s just weeds. Funny looking dirt.
not sure what vegetation you're looking at the little yellow orange specs are just a few leaves that have fallen overnight. I've been removing all the roots that I've dug through as I went along. The section in the foreground is basically undisturbed after having cut down the top and spread it back in the back on top of broken concrete and brick.
I was wrong, was 60 40 40 30. now 70 all around cuz i read on the tire 75...I assume harder is better to compact?
well it settled a little after I marked the lines so disregard those but after 2hrs I have 2 in of sand and 1/16 in of silt if I'm correctly reading the directions of the jar test. now I have to wait two days to measure the clay. very slight bits of floating stuff on top which I assume is the organic. The directions called for powdered dishwashing soap and all I had was liquid so hopefully that doesn't skew the results that much.
I did residential subgrading for awhile, all we used was skid steers. We could pack it hard enough to roller blade on. Always tried to keep the bucket full for weight and constantly offsetting tracks. Also always kept the bucket down. Going forward the lip slightly up dragging the heel of the bucket Backwards the heel slightly up dragging the front edge. Rarely ever drive around with the bucket up. Every trip counted for compacting it.
Chunk of 1/2 rotted wood - When I zoomed in on the other pics there some roots and other fragments. Just my $.02
I see what you mean, good eye. Yeah I've thrown out a ton of those as I see em
I'd still do what I suggested. Throw down the gravel and run the plate over it at the very end of the job. It's nice to compact that gravel. The site looks great by the way.
Thanks man, we love our backyard...I actually hate uglying it up with a building but ...
I've seen folks talk about backdragging with the heel of the bucket...mine is 4" above grade when lift fully down. Bobcat 743
Don’t backdrag with heel of bucket, makes you ****** operator. Lol Wear out back of bucket. My dad is famous for wearing the back of every bucket he’s had over 40 years, maybe 50. Lol
Some buckets are designed for back dragging with the heel. It is the best for leveling in many applications. I wish more buckets had extra meat in the heel or had replaceable wear plates.
There's not much clay left in that water, judging from how clear it is. If that much is sand then I don't see any problem with compacting this soil, sure doesn't look "rich and black" from here, the color can be deceptive, low oxygen iron will look dark, but lighten a lot when exposed to air. Are you sure you shook the soil enough to dissolve all the particles, if you take a spoon of the top 1/2" will it feel sandy/gritty?
AB3 $21/ton Looks like I'll need 150 - 200 T. Thanks for reminding me of the vegetation, I had forgotten to strip some sod in a couple spots,...I got too excited trying to fill the low end lol... had to go back and rework that.
You're welcome. That's why were here to discuss all sorts of things related to construction and heavy equipment. Is that $21 per TN delivered? 200 TN is 8 tri-axle loads of roughly 18 CY per load for around 140-150 CY of material. How deep are you planning on filling with rock?
Yes, delivered...used to be $15ish. I've got to bring the low side up 1.5 - 2 ft. And slope around the perimeter a few feet, plus one corner is dropping down into a gully so i'll have to somehow compact that area up in shelfs and lifts I guess. It should be closer to 120 - 150 but not sure. They brought my first 30T in a dump truck yesterday.
Contractors in my area quite often weld modified cutting edges on the back of skid steer buckets. Have you considered putting geo- tech fabric over the pad ? I have had good results with it.
$21 a ton is cheap compared to what we pay here. Got a quote this week for #57's (3/4 washed) around $27 TN delivered and that was for 1400 TN. The quarry is less than 10 miles away. Do you have any dirt you can build the slopes out of? As long as the stone goes outside the slab footprint 2-3' you should be ok. Geotechs spec 5' outside the building edge for structural fill but that includes the "engineers overage". You're not building a 4 story hotel. Basically build your stone pad up. Pour your slab and then backfill with dirt around it. We used to build house slabs like that here all the time.
Man that’s gonna be a lot of gravel. If you have the money to burn. I learned to operate equipment from a guy that had about 3 teeth. He told me , if there is a cutting edge, use it, that’s what it’s there for. I have pulled operators outta a couple of machines after nicely explaining that, while the back of the bucket is easier to grade with, the cutting edge is there for a reason. I haven’t seen a bucket with a back pad on it but I have certainly welded up quite a few worn through the bottom back. If it’s a little bit of loam, that one thing. If you’re grading 40 tons of gravel with the back of a bucket, you’re sloppy.
If you're doing a lot of backblading then welding something on the back of the bucket is a good idea. I remember JD advertised the buckets on 655B and 755B track loaders had improvements for backdragging/leveling. It was like a thick angle iron on the back of the bucket instead of the standard curve of the earlier buckets.
I feel better already lol I just saved $6 a ton So I'm picturing compacting the stone (ab3 1"minus) a few feet outside my perimeter then coming back with a 12" bucket and carve the turndown around the outside edge. curious how good the wall of the trench will hold up. and yes to the backfilling with dirt.
Can you get your machine all the way around the pad? If so layout your corners and cut back the stone however far you need to. We do this for retainer walls and tall turn down slabs all the time on commercial jobs.
Depending on how cohesive the material is, fill will stand up at about one half to one at the very steepest.
1/2 vert @ 1 horiz ? ( AB3) what if I had a deeper turn down in the one problem corner than the rest of the slab? is that going to create a differential bending moment in the slab? put a bunch of extra steel in that corner? to make matters worse in that one corner I had to take down a 90-foot tall walnut tree The base of which is just outside of the footprint so over the next 150 or 200 years those roots will rot.
and you'll be long gone.
thank goodness lol
do i want to compact the ab3 to 2" below the conc then put 2" clean on top of the ab3 or will the compacted ab3 give enough drainage under slab? actually where I have 2" gravel I put plastic on that then 1" sand on that then rebar and conc. the plastic reduces sweating/dampness and the sand on top absorbs the bleed water in the pour so if i want 5" conc and 1" sand do i put the ab3 to 8" down and add 2" clean or put the ab3 right at 6" below top of slab?
I prefer a capillary break under slabs. Standard here is 4" of #57's (3/4-1.5" washed) under the slab with vapor barrier over that. 2-4" of 2" stone should suffice for a capillary break. The DBG will make a good base under the entire slab.
do you add sand on the vapor barrier or pour directly
Always poured directly on VP. The bleed water coming off is part of the heat of hydration curing process so let the water bleed off "naturally".
so I'm getting pretty close to height on the overall footprint. this lowest corner is my big fear factor. I've been building it up and compacting it in four to six inch lifts to get up to this high. but I need to go another six inches or so and the breakover point where it's slopes is right at my string line edge of concrete. so I need to keep going a little bit to the left but I don't know how far over the edge I can run my tires before I end up sailing down into the hole. soon I will have to rent a mini excavator to dig my 3-ft trench footing around the perimeter and thought maybe I can whack the slope surface down with the bucket? I'm very fearful of driving parallel to that slope to pack that last bit of edge.
Got any 5” minus or big stone you can cast over?
Dig overburden off, backfill with gravel. Slab over topsoil?!!
70?! I run 45psi in my S250. Tires I think are rated to 50.
I paid $9/ton, but that with me hauling it. Can haul about 15 tons a trip, pit is less than a mile away.
no the slab is on compacted AB3
these tires were reated at 75 And I thought hard would be better for compacting but then I read somewhere it might be less bouncy at a lower psi so I pulled them back to about 40
743 is what, 5000lbs? I wouldn't trust compaction with that vs the $300 to rent a compactor.
Your building too close to the edge of the pad IMO. That pad should have been several feet larger than the footprint of the building, especially on the down hill side like that.
It needs to be a larger area and what's there doesn't look at all compacted. It needs to be done in layers and also needs some moisture to get fully packed.
If you are digging a 3' deep trench footing for the perimeter just dig back down to original grade and pour back if you are concerned.
I've spent a lot more than $300 on the compactors :-( I've been using a jumping jack and a plate compactor plus driving on it with the bobcat.
That's the surface couple inches on the slope that I don't know how to pack down cuz I don't think I can drive down that steep of a slope. everything has been in four to six inch lifts, wet, and each layer compacted before adding the next and stepping up the slope till I got to grade. if / when I get the excavator I think I can reach over and smack it down with the bucket just to clean up that surface.
You always want to over build pads past the footprint of the structure. A typical over build is about 5'.
oh sorry man I see what you're talking about, I have just spread the last layer on top and have not rolled that yet. I was just talking about the loose slope area and wondering how I could get some compaction on that to reduce erosion runoff
yeah I have plenty of space around the footprint all except for this one low corner. And I'm up against a little drainage area that's not a creek or a stream but does run a couple inches of water once or twice a year after heavy rains
it's getting flatter every 30 tons lol