Stability of new fill

[Retire]

Okay, I have been lurking here for awhile and finally have the nads to post my question. Planing on building my shop soon and am still deciding where to put it, the place I prefer is the area I recently filled in with excavated soil and rock from a nearby road job. The area was filled over the coarse of about 4 months and I did attempt to make sure there was no voids and even soaked the area while it was filled. It has been 4 years I have planted grass and have had no sinking issues. My question is will this be a solid enough base for my 2 story 24x30 gambrel barn? I live in Massachusetts so I would go with a four foot footer with a four inch slab. To make matters worse I did take down some average size trees and left the stumps in the ground.
The stumps would be approx 8 feet below the current grade and each stump has a boulder five times the size of the stump. The fill was rather rocky but again I was cautious to make sure any voids were filled with sand. I would ensure to bring in some good base material and pack it well. Or should I just position my building someplace else. I really want to place it on this proposed site. Thank you for any feed back.

 

[PT Doc]

The only way to know for sure would be to have the soil tested. I would want to be sure. Just because it has not sank, doesn't mean it wont.

 

[383]

That is a tough question. It could be fine, but if it were mine I would bring in a soil engineer to do compaction tests.

 

[f150skidoo]

oops multi post

 

[f150skidoo]

I'm know expert but 4 years of weather should have the ground good and compact. But you won't know for sure until a shovel is in the ground and you have a look for your self.

 

[Retire]

Okay 383 I think your messing with me. Exactly what does a soil engineer do? Oh ya and where would you find one and how much do they cost?

 

[LB-1911]

Okay 383 I think your messing with me. Exactly what does a soil engineer do? Oh ya and where would you find one and how much do they cost?

What Is a Soil Engineer?
The job of a soil engineer is to analyze the soil structure of a proposed building or construction site and to understand problems of existing structures due to conditions of the ground underneath them.

http://degreedirectory.org/articles/What_is_a_Soil_Engineer.html


Geotechnical Engineering Services Suppliers serving Eastern Massachusetts

http://www.thomasnet.com/eastern-massachusetts/engineering-services-geotechnical-26205005-1.html

 

[southalabama]

I didn't have a soil compaction test done but the dozer service compacted heck out of it with dozer. They went back and forth over and over. It wasn't just piled up. Also be wary or organics. Roots etc. you need to be at sterile dirt.

 

[Retire]

Jesus. Learn something new everyday. I will call Monday , there's a place next town over. Hope it doesn't cost too much. It does seem over kill but I want to do it right. Have to wait until they are done running the septic main anyway so no rush.

 

[Retire]

Southalabama. That was one of my concerns about the stumps eight feet down. But like I said I had massive boulders placed over them. Never thought I would put the barn out front when I was filling it in. Always thought the thing would go outback but to long of a run for septic. Plus the thing is gonna look so good I want it out front

 

[TractorJeff]

I don't think stumps 8 feet down will cause an issue.
They need air to rot fast, so you will be dead and gone by the time they breakdown.
The boulder over the top will act like a bridge to support what ever is over top.

 

[c39er]

A dozer really does not compact soil too well. Not too many Lbs per square inch depending on track width.

 

[Junkman]

There is a building in a shopping center in Central Massachusetts that had stumps buried under the floor, and they were about 30' down. One winter day, the weight of the roof drove one of the steel beams through the concrete floor, and down another 4'. I worked for the property owners, and they patched up that one area. When the tenant left, they cut a hole in the concrete floor, and there was nothing under most of the floor. The building was disassembled, the ground was excavated, and all organic matter removed. Then they started to fill in the hole with material, that was compacted every few inches until they got back to ground level. Once the new floor was poured, they put back the original steel work and blocked in the sides again. You might not see your building settle, but someone will. The only thing to do is either dug up the stumps, and logs, or plan on some other location. Be honest with the soil engineer, so he knows what he is looking at for problems.

 

[TractorJeff]

What he says is true, neighbor drove his skidsteer through his own lawn last week.
Rutted the Devil out of it.
I went over to dig a stump out for his wife.
He and I looked at it, he says maybe in a couple of weeks.
Told him, No, tracks lay at 2psi on 14" tracks, I'll float over.
I drove over to prove I was right, dug out the stump, filled in the hole.
On my way out, back filled a trench project he started last fall and never finished.

 

[brownbagg]

yes it will settle. the tree will rot out creating a void, something going fall in that void till it reach a footer or slab and then the bldg falls in. yes it make a good movie but basically, it will settle

 

[inphx]

The soils engineer will do core drills and find compaction variences if they exist. A cheaper solution to excavating and compacting is a design where stem walls dig down and find the native ground and a slurry concrete pour is used to bring up to the footers... that still leaves the slab with some doubts the soils engineer can advise you on.

 

[nolimits76]

FYI, the "soils engineer" you need is a civil engineer. You can have sample borings taken of your soil using different labs. The report should be finalized and stamped by a licensed & registered professional engineer (PE) -- again in the civil discipline.

The good and bad is that boring reports take physical samples to determine what is underneath. They give a fairly accurate representation of what to expect; however, keep in mind they are location specific. So going 20' away from the boring sample could yield different results. For this reason, you typically formulate a plan where you would like to build critical footers, drilled shafts, etc and then sample as close to those areas as possible.

While these costs can be kept under control, this may be problematic for the average home owner. Is your property located in an area that you could do this research/analysis and with favorable results develop the area and sell out commercial plots? If so, it might allow you to make some money to buy property without potential issues.

The soils engineer will do core drills and find compaction variences if they exist. A cheaper solution to excavating and compacting is a design where stem walls dig down and find the native ground and a slurry concrete pour is used to bring up to the footers... that still leaves the slab with some doubts the soils engineer can advise you on.

Building bridges, we do something similar. We examine the boring reports (mentioned above) and then use speciality drilling machines to drill down to the rock socket. We go in 5' and then pour a drilled shaft that eventually becomes the columns you see when driving by. Of course those columns support beams and ultimately the bridge deck people drive on. My point being, drilled shaft operations can be VERY expensive. Diameter size and depth combined with what you are drilling through will determine overall costs.

I have worked with some private clients in similar situations (but for commercial properties) and they were investing in 24" to 48" drilled shafts under their slabs.

Alternatively, depending on the soil analysis it might be possible (and cheaper) to use a geogrid material to reinforce the earth and prevent the sink holes. Think reinforcing for the subgrade material. Here are a few links:

http://www.maccaferri-usa.com/solutions/roads-pavements/sinkhole-remediation/17234-1.html

http://www.huesker.com/uploads/tx_i...ents_on_Soft_Soil-Fortrac-New_Orleans-USA.pdf

http://www.tensarcorp.com/Systems-and-Products/Tag/Tensar-Geogrids

 

[Ajustable]

The soils engineer will do core drills and find compaction variances if they exist. A cheaper solution to excavating and compacting is a design where stem walls dig down and find the native ground and a slurry concrete pour is used to bring up to the footers... that still leaves the slab with some doubts the soils engineer can advise you on.

We recently had to do the slurry concrete route so that one side of the foundation wall was supported across Non virgin soil. that is that the soil was previously dug and filled.

The product we used was called K crete, it was said to be a weak concrete mix and forms a bridge across the unstable soil. We needed an engineers stamp before we could proceed. It worked out OK, but we ended up paying more for delays and material. Plus because the virgin soil was 8' down in the trench no one was allowed in the trench because of safety rules.

An engineer will know all your options in regards to your build, best versus cheapest. Good Luck

 

[nolimits76]

I might also mention that if you expect potential subgrade movement then using a post tension slab might be worthwhile. First you need to deal with the soil problem.

Moving to the slab, installing these tendons and then having them tightened (tensioned) afterwards can keep your slab intact with minor soil movements. They are quite popular in OK due to clay soils that tend to move (shrink/expand) more than some soils.

Again, it does nothing to keep your soil from sinking but rather preserve your slab if you have some minor movements. So make sure you address the soil problem first. This is just an FYI for your slab.

 

[rieferman]

When I was selling construction, I worked for a no-shortcuts outfit, and I had a great excavator (still does work for me at my own house) who was similarly minded. I would frequently lose business because site prep can be a big number when truly done properly. Most would feel that it was "overkill" and not worth the expense, and it really seems that way at times. But, google and this website are filled with stories of buildings that were killed by the land they sit on. Mother nature is tough to beat when corners are cut.

Anyways, all that to say this... I think it's good that you're trusting some good advice in this thread and bringing an engineer out. If you're honest with him/her and get a good plan of action in place, you'll never regret it.

 

[nolimits76]

Plus because the virgin soil was 8' down in the trench no one was allowed in the trench because of safety rules.

An engineer will know all your options in regards to your build, best versus cheapest. Good Luck

I don't know your situation, but trench boxes can (and should) be used in deeper trench excavations to prevent soils from collapsing on workers inside the trench areas. We've used them quite a bit when doing various pipe and drainage structure installs.

FYI, be cautious trusting an "engineer's estimate" for construction services. Working in the industry I can tell you many are not very accurate. The more accurate ones typically work with a construction firm to determine costs. The engineer forwards his preliminary reports and recommendations to the contractor and they put together a loose budget. From the contractor's side it usually feels like the equivalent of a napkin sketch and consequently the contractor estimates high (because of the unknowns & risks that many engineers are oblivious to). As the plan becomes more developed, a more accurate and reasonable cost proposal can be provided. Put together a formal bid and invite 3 or 4 contractors doing the same type of work and prices will get more competitive.

 

[mygarageone]

A dozer really does not compact soil too well. Not too many Lbs per square inch depending on track width.

Exactly , they can run a dozer over a drain field and not hurt it , that tells you something.

 

[nolimits76]

Exactly , they can run a dozer over a drain field and not hurt it , that tells you something.

Use a sheepsfoot for soil compaction, not a dozer.

 

[brownbagg]

you need to locate those tree stumps, so get an excavator and start digging

 

[Retire]

Too expensive for for such a small structure. I guess I will just relocate my building. Thank you all for your replies. As you can imagine I could never locate six or seven trees eight to ten feet down and the cost would be prohibitive given that each one has a huge boulder over it.

 

[Retire]

Also I left no logs or other organic material before being filled just the stumps. Well this ***** because now I have to convince the wife that it would look better on the other side. Any suggestions on that!

 

[nolimits76]

Also I left no logs or other organic material before being filled just the stumps. Well this ***** because now I have to convince the wife that it would look better on the other side. Any suggestions on that!

Sure, get a quote to do it in the spot she wants. Then show her a quote to do it on the other side. I'm willing to bet you won't need to say much else.

I know this *****, but you are wise to figure it out before you build something on top of a potential sink hole. If you can simply shift the location of your land, then you can avoid lots of liability and additional costs. It seems logical to live with a new location.

That being said, I would be sure to place my building on land that is far enough away from the filled spot so if it does sink you don't have "collateral damage".

 

[Retire]

Yes sir, other side of the drive way a good hundred feet away. All sand over there but i know its virgin soil.