Preparing a building pad

[rockasawrus]

Hello All,


I'm building a house in NY and naturally the first step is to prep the building pad. It's my first time doing this so I'm feeling a bit nervous about the whole thing. I'm hoping kind, experienced folks can review my plan of action and give suggestions/insight. Much appreciated!


The building is a 32x56' pole barn with a 10' wide patio on the front of the building - 4' deep piers and 5" floating concrete slab - wire mesh and fiber mesh as spec-ed by engineer.

I dug a 24" deep test hole the other day...If I'm reading it right, the topsoil appears to be fairly shallow, about 4-6". It's not too obvious when looking at the layers, but the subsoil is quite a bit yellower.

So the plan is to:
1) Dig out 10-20 stumps under and around the building pad. These range from 12-36" diameter, thinking I'll rent a 30 ton machine for this.
-Is backfilling with subsoil or fill and compacting with excavator bucket enough? Or should I run a vibratory plate over these?

2) Scrape off the top 6" of a 52x66' area and put it in a pile for spreading later. Should be approx 73 CY with fluff
I'll do the same to connect the existing driveway to the new building as well.
- Not sure what the best machine is going to be for this - I can get a 75hp tracked skid steer or a 77hp Cat dozer locally. I've never run a dozer before so not sure how efficient I'll be with that. Would using the 30t stumping excavator for digging and skid steer for moving material be awkward/overkill? I feel pretty comfortable operating excavators but the biggest I've used is 12ton

3) Bring in fill and compact in 6" lifts. Back corner of building is high maybe 12".
-Do I have to bring the rest of the pad up to this grade, or can I make kind of a swale to push water either side? I'm in radon zone 1, so planning to install radon mitigation under slab. Engineer wants 6" gravel/crushed rock under the slab. Would it be worth doing 2" ROB and 4" clean gravel, or just use 4" clean for the whole thing? My wallet is hurting thinking about it.

4) Bring in crusher run to bring driveway up to grade



Thanks for reading!

 

[4570Man]

A 30 ton excavator is pretty excessive to dig 20 stumps. Sure it would work but the rental would be expensive and the transport cost will also be expensive. A 10-15 ton excavator would be plenty sufficient for that work and much cheaper to rent. I’d probably rent the skid steer over the dozer. A skid steer is pretty capable at getting work done and a lot easier to learn to operate over the dozer. Use the money saved on the other rentals to get a good size compactor roller. A plate compactor makes the surface look good but it’s only good for 1-2” lifts. It takes way too long to get anything done at that rate. Just tracking the dirt in 6” lifts or so works pretty good as long as the material is right if you didn’t want to rent the roller. The correct moisture for compaction is a pretty slim range. You can’t compact mud or dust.

 

[paulsharvey]

So, 1st, those 36" stumps, are they within the building footprint/slab? If not, I'd grind them. A 36" stump, in what appears to be a pretty clay heavy soil can be a son of a B to get out, but I'd feel fine with a rental Cat-318/Pc170 or similar; unless you have other specific uses for a 330/300.

I agree that it looks like I'd call top soil maybe 6", but it's not really a mater of the top soil, it's about removing organics, which includes any roots bigger than your thumb.

Backfilling a stump hole, the hole for a 36" stump, at the least, put somw.matwrial in (approx 6-12") and pack it with with the hoe, then add more, pack, add more and pack. Your never going to get to 95/98% density just packing with a bucket, unless we do it in lifts

 

[Rockbadchild]

So the plan is to:
1) Dig out 10-20 stumps under and around the building pad. These range from 12-36" diameter, thinking I'll rent a 30 ton machine for this.
-Is backfilling with subsoil or fill and compacting with excavator bucket enough? Or should I run a vibratory plate over these?

one or the other should be fine, you will need a diesel vibratory plate to compact your gravel under the slab regardless

2) Scrape off the top 6" of a 52x66' area and put it in a pile for spreading later. Should be approx 73 CY with fluff
I'll do the same to connect the existing driveway to the new building as well.
- Not sure what the best machine is going to be for this - I can get a 75hp tracked skid steer or a 77hp Cat dozer locally. I've never run a dozer before so not sure how efficient I'll be with that. Would using the 30t stumping excavator for digging and skid steer for moving material be awkward/overkill? I feel pretty comfortable operating excavators but the biggest I've used is 12ton

I would use the excavator to do this, the skid steer is also a good option

3) Bring in fill and compact in 6" lifts. Back corner of building is high maybe 12".
-Do I have to bring the rest of the pad up to this grade, or can I make kind of a swale to push water either side? I'm in radon zone 1, so planning to install radon mitigation under slab. Engineer wants 6" gravel/crushed rock under the slab. Would it be worth doing 2" ROB and 4" clean gravel, or just use 4" clean for the whole thing? My wallet is hurting thinking about it.

Not sure what this mean in red ...

No, follow engineer recommendation I would used 3/4 inch minus crush gravel.

 

[Rockbadchild]

A 30 ton excavator is pretty excessive to dig 20 stumps. Sure it would work but the rental would be expensive and the transport cost will also be expensive. A 10-15 ton excavator would be plenty sufficient for that work and much cheaper to rent. I’d probably rent the skid steer over the dozer. A skid steer is pretty capable at getting work done and a lot easier to learn to operate over the dozer. Use the money saved on the other rentals to get a good size compactor roller. A plate compactor makes the surface look good but it’s only good for 1-2” lifts. It takes way too long to get anything done at that rate. Just tracking the dirt in 6” lifts or so works pretty good as long as the material is right if you didn’t want to rent the roller. The correct moisture for compaction is a pretty slim range. You can’t compact mud or dust.

when we did culvert we did 4'' lift for 3/4 inch crush and 12'' for sand with heavy diesel plate and proper moisture (1 to 2 inch is not much at all maybe for a mini gas vibratory plate)

 

[rockasawrus]

Thank you all for your replies, feeling like I'm almost ready to tackle this!


I got confused about the excavator size. I meant to say a 30,000# machine or 15T, so looks like I'm in the ballpark. I think I may rent the excavator for one day, so I'll see how many stumps I can manage to dig out, the rest I can grind or otherwise deal with down the road.

That's interesting about the vibratory plate, I have seen many people use them for more than 1-2" lifts, but from doing some reading, it does seem like the more official rule of thumb is 1" per 1000# force. Oddly enough, my local rental place has a 20" plate and a 1 ton roller and they both put out 3000# eccentric/centrifugal force. Guess I will need to get a larger machine if I want to do higher lifts. Getting proper moisture is going to be a bit tricky as there's no water on-site yet, might have to figure about getting an IBC tote up to the site or wait for some rain.


About the grading around the building, I wasn't too sure what I meant either but after thinking it through, I guess my question is can I do a combination of cut/fill (Option 2)? I think bringing more fill (Option 1) is probably the better way to go to keep water away from the building. It looks like I will have to cut a little swale either way to direct water away from the building, as I'm not at the highest part of the property. Am I thinking about this right? See attached pics below (blue is pole barn)

So my strategy will be to scrape off topsoil, spread and compact ROB up to 6" below highest side of grade (if needed, probably only on left side of building), and then spread and compact 6" crushed rock to match highest side of grade. Finished floor will be 8" above grade.

How much extra material should I add to what I need to figure for compaction?

 

[rScotty]

It almost sounds like the "engineered design" was done before the test holes were dug and subsurface conditions were considered. Maybe I'm just reading it wrong. But if they didn't do much investigation, you may want to get your money back and get some design work done in the proper order. Probably not much will change - and now you have the pits dug to look at. Getting a real engineer involved might save money in the long run....& it's generally better a few years later.

 

[Quaffer]

I think I may rent the excavator for one day,

What do they charge for rental?

 

[Rockbadchild]

It almost sounds like the "engineered design" was done before the test holes were dug and subsurface conditions were considered, If so, you may want to get your money back and get it done in the proper order. Probably not much will change, but getting a real engineer involved might save money in the long run....& it's generally better a few years later.

lol a real engineer ??

for ops post #1

''The building is a 32x56' pole barn with a 10' wide patio on the front of the building - 4' deep piers and 5" floating concrete slab - wire mesh and fiber mesh as spec-ed by engineer.''

''3) Bring in fill and compact in 6" lifts. Back corner of building is high maybe 12".
-Do I have to bring the rest of the pad up to this grade, or can I make kind of a swale to push water either side? I'm in radon zone 1, so planning to install radon mitigation under slab. Engineer wants 6" gravel/crushed rock under the slab. Would it be worth doing 2" ROB and 4" clean gravel, or just use 4" clean for the whole thing? My wallet is hurting thinking about it.''



Ops said he has engineer slab drawing that comes with sub base... I have never heard of test holes for a residential floating slab, they usually simply ask sand or clay. I got my design for my slab which was structural footing and slab and they ask location, soil type (which is clay) and they did the design.... Ops soil look like more sandy then clay but still most likely sandy clay.

 

[rScotty]

There are lots of ways to build things. The OP says he wants to float a large slab on what is probably unevenly expansive clay soil - "expansive" meaning the soil changes shape and strength with different levels of moisture and pre-compaction.
I've never heard of a foundation design where the engineer didn't first take a look to see what kind of substrate he was dealing with - especially when using 6" lifts.

There was a time when I just charged ahead. But I'm old enough now to recognize when I would want more information. The OP might too.

I hear him on the expense. But knowing the choices is worth something too.
rScotty