How long should I let new ground settle before putting in posts on piers?

[rlneal]

Thanks for all of the replies. They have been helpful and reassuring. Responses to certain individuals:

Yes, it is a pole barn. Our original thoughts were to make it 30x80 with space included for a cattle loading shute, hay storage, storage for a travel trailer (my son may want to live there someday, he says), and a concrete pad next to the travel trailer. Don't think we will be able to accomplish all of those goals. Such is life on hilly land.

The bulldozer man is a good guy but his experience is with doing farm ponds and other types of grading. Probably not so much grading for a building. I asked him to scrape off the top soil first so we could use it to put on top surrounding the outside of the building perimeter. He did a fair job of that. I had considered digging out the rocks with my tractor loader as he pushed them out but then did not do that. There were a lot of them.

Manual post hole auger --- My nephew has one that was given to him by his mother. I think she got it at a garage sale. I have been looking to buy one for years and cannot find them anywhere. All I can find is the clam shell type.

Another problem we are going to have to deal with is water run-off from the hill above. This area has been quite wet in previous winters. Not sure if it caused by actual run-off from the hill above, which could be solved with a small trench to drain it around the building, or if it is water coming through the rock layers from up above. Either way, I figure I will have to put down a fair amount of crushed rock. Might also put down pallets on the ground to set the round bales on.

 

[Egon]

Drilling rig and bell holes.

 

[orezok]

There are 2 other methods of compaction, if you can afford them. First is dynamic compaction. A crane lifts a 5 to 10 ton weight up to 100’ in the air, drops it and will compress the soil up to 5’ and to a depth of 30’ or more. Move over a couple of feet and do it again for days. This was used on a high school site adjacent to the district where I was a Facilities Manager. The alluvial soil was too deep to excavate and recompact. The second is vibrocompaction also called stone columns which I used on a middle school site. Here a 24” hole is bored up to 30’ deep on an 8’ grid over the entire building area. Then a vibrio probe (think gigantic vibrator) is lowered into the hole and energized. Rock is dumped into the hole with large quantities of water as the probe is maneuvered up and down. The vibrator compacts the soil horizontally and the rock fills in the voided space, thus “stone columns”.

Now I don’t recommend either process for your site as both are six figure remediation which on $50M to $100M projects is not significant.

YMMV

 

[dodge man]

My recommendation would just to put the post a little deeper in the fill area. They make augers that go on excavators that are hydraulic powered that will easily make those holes. That wouldn’t be that expensive.

 

[fried1765]

My recommendation would just to put the post a little deeper in the fill area. They make augers that go on excavators that are hydraulic powered that will easily make those holes. That wouldn’t be that expensive.

That is essentially what I suggested in my post #4, but still does not address the concrete floor issue.

 

[KWentling]

The least I would do is drill piers to undisturbed soil so the building itself will not settle. You can add fill to keep the interior level as it settles. If you're going to have concrete, I would start over with proper compaction and pick out the bigger rocks and debris. That much fill would take a life time to settle.

 

[buckeyefarmer]

My pole barn needed 20” footers under each pole. I rented a skid steer with 18” hydraulic auger and then took a little off the sides at the bottom to get 20”. You need footers on virgin soil.

 

[Varmintmist]

The water run off is great for what you need. Dam the perimeter and let it flood. Dont drain it. You do that and you will get as much compaction as you are going to. Let it sit for a year. I would still go deep with your piers, but you will be filling in with as much compaction as you will get.

 

[BeezFun]

I had a similar situation but smaller building, I dug the holes deep, that's required here anyway for frost heave. Not sure what your weather is there but on the edges of that built up area the frost is going to penetrate sideways quite a ways. I added about 12" of CA6 (gravel mix) to be the floor of the building for a few years. After a few years of that settling I poured concrete and it's been ok. You do have deeper soil at that downhill end, but if you don't notice any settling after a few years, I'd go ahead and pour on top of the gravel base.

 

[robisinwa]

We have a lot similar to yours... gentle slope from right to left of where I wanted to put our barn. Instead of back filling half of the pad, I dug down into the hill side and end up with the barn 5 feet in the ground on the up hill side so my pad was all virgin soil. It also allowed the barn's height to be out of the wind a little more by being lower profile. We put a retaining wall on the up hill side and then the posts are on the inside of that, in the ground, holes dug in virgin soil. Just a thought.