Building a garage on Fly ash?

[Crazy Legs]

Hey everyone, I'm located in Iowa and heading into winter, next spring/summer i'm going to be building a 24x36' garage in my backyard, no biggie but my backyard has some slope to it and already brought in 26 tons of bottom or fly ash to use as fill to bring it up level. but now i've got this 3-4' drop off at the back of the building site. i set up old busted up concrete pieces, bricks, you name it & its probably put back there to hold the fill from erroding away but i'm worried that once the garage is built that it'll start eroding or the concrete slab will slide off this thing...... or am i just over reacting?
Oh btw, i've compacted the fill and its very solid but when it dries out its like compacted sand, but about 2' from the edge where it drops off its like quicksand so obviously its not stable to build on.
Should i put clay behind this or on top etc or railroad ties, more concrete pieces?
Any help or suggestions is appreciated

 

[boiler7904]

If you're haveing problems with compaction and stability now, that will only worsen with construction traffic. There are a couple of options depending on budget and space.

If you have room, you need to reduce the slope at the back side of the building site. Bring in more fill material and compact it so that you have a gentler slope.

The other option if you don't have a lot of room is to build an engineered retaining wall. I'm saying engineered for two reasons:
1. You're 3-4 feet tall which is usually the cut off for not needing an engineer's stamp.
2. You are about to have a building in close proximity that could transfer loads to the wall depending on how close you are to the wall.

 

[Crazy Legs]

yeah i just read an article on the engineers stamp on the height of drop off etc. so i'm at my limit for height. One thing i for got to mention is where this drop off is in the back of the future garage is woods area and not my property so i have to be careful but for the most part as long as i plant grass on this slope this guy is good to go And this will be a concrete slab i'm putting on this fill. do you think if i get this compaction figured out it'll be ready for construction next spring after sitting for a winter? (aka freezing/thawing of the ground)

 

[Itzkwik]

I would do some checking on using the fly ash for a base material. Several years ago here in the Richmond, VA area, Home Depot built a new store that was on a fly ash base. Several weeks before the store was ready to open, they noticed huge cracks forming in the floors due to uneven settling. They ended up having to tear the entire building down. Not sure, but I think they have banned using the ash for a base material here.

 

[Crazy Legs]

thats my exact worry!! the reason i used the fly ash was because my buddy added 5' to his grade and built a 28 x 40' building on it and it was 1/2 the cost of other fill and it looks great to this day, but he's superman and everything he touches turns to gold........ me, i'm more like hermit crab lol

 

[nitro520]

Ksths2 I think I can help you out some on your fly ash or bottom ash problem. There is a difference between bottom and fly ash. From your description I would say you are refering to fly ash. Is it tan in color? Is it purely a fine material like 1/8" minus(no pieces bigger than 1/8"). I live in Coloarado and we sell bottom ash and fly ash. We use alot of fly ash for road and building stabalization. Fly ash needs to be mixed with the soil and have water added to stabalize. If you just put in lets say 1' to 2' deep and compact it, you will not have a stable foundation. You need to use water and hydrate to around maybe 14% and mix with the soil. Depending on your situation you might be able to use a heavy duty rotatiller and mix and compact, but how it acts with your soil I do not know. Some soils and some fly ash react different. I definetly would not build on what you have even if it sets throughout the winter. I would either figure out a way to mix and compact or possibly remove it and get some compaction sand or whatever they use locally. I hope this helps a little. Let me know if I can help more.
Mike

 

[Crazy Legs]

hey nitro, yeah this stuff looks just like sand aka 1/8" at biggest and tan when its dry. Can clay be added or put on top of this ash to help stabilize it?

 

[nitro520]

hey nitro, yeah this stuff looks just like sand aka 1/8" at biggest and tan when its dry. Can clay be added or put on top of this ash to help stabilize it?

No, the problem you have is you will have pockets of ash under the clay even if the top is hard. You might be able to mix some sand and mix in with water and compact, be you will have to go all the way to the bottom of the ash. The best would be to pick up a little of the existing soil when you do. I know this is not the best news to hear, I just don't want you to have future problems.

 

[Crazy Legs]

ooohhhh, i hate that since i just had 26 tons of that stuff brought in last week and got er' all leveled out etc.......you got any rope or something sharp i could jump on lol?