Low compaction fill? Frost?

[RoxyOttawa]

What is the best type of fill to use under a garage slab? I need to fill an existing basement by 4 feet deep and want to minimize the chance that the footings will freeze and at the same time I want a stable base for the slab which will not settle over time (since I will have some wood framing on top of the floor that connects to another foundation)

Where can I find out more information on how much different types of fill will compress. ie: Granular -a ,b c, 2" crushed rock etc.

Thanks Rob

 

[DRC1]

I would suggest 3/4 inch stone. (2 in. stone is tougher to work by hand and wont yield any better results for your application.) Tamp well with a small tamper and you should have very little settlement. If at all possible, install a drain pipe (Corrugated ABS works well - use 6 in. nad you won't regret it.) Wrap in filter fabric, place at the botom of the excavation, but not under the footing and pitch positvely to drain.
Good Luck!

 

[RoxyOttawa]

Okay Thanks.

If I go for 3/4 stone (I guess that would probably be size 0 to 3/4 inch stones). Do you know what percentage increase in volume I should order to compensate for the reduction in volume when I compact it? A local sand and gravel company tells me no more than 10%, but I've heard of numbers as high as 30%.

I need to fill about 36 cu yards. So I want to avoid being 20% out and having too much.

The part about frost - there is an existing concrete floor which I was just going to put gravel on top. The floor has a drain which I'll use in the unlikely event of a flood. But, I was wondering if the stone is equivalent to soil and act like a heat sink, in that the frost line will not go below 4 feet if the garage is left unheated.

Thanks, Rob

 

[dirtsqueezer]

RoxyOttowa,

For volumes, I would just order rock according to the 10% rule. Your actual volume estimations may differ from how the site is actually excavated. If you need more, it seems like for 36 yards of fill, an extra truckload or two would make up the difference. When I take readings on a loose pile of 3/4" rock, I generally get around 75% dry density (this may sound a little...involved, but) An increase to 95% would mean a little over twenty percent decrease in volume. I would, however, take it from the horse's mouth. That is their business, and I doubt they'd recommend you buy less of their product than more!

I thought this was an interesting discussion on drains: thread256-81923

I agree with DRC1 that your drainage may be more at issue for frost heave than the actual material type. I would just be sure you had your fill properly compacted, such as with a jumping jack (a very cheap rental), and placed in 1 foot lifts, so you don't have problems with settlement. Crushed rock generally has little fines, and so will drain well, if the groundwater has a place to go.