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Huge Trench in Basement Floor

5K views 21 replies 6 participants last post by  beenthere 
#1 ·
Hey!

So in order to put in a new pipes in our basement, we had to big up a huge trench in our basement floor. It is around 12 feet long, 2-3 feet wide, and a 1-2 feet deep. (I'm estimating, I didn't dig it, nor am I looking at it right now.)

What do I fill it in with? Gravel and sand? Concrete? Gravel and Concrete? Gravel, sand, and concrete? What do I do.

Thanks!
 
#4 ·
Concrete slab should be re-installed on a bed of compacted CA6 aggregate or similar product with compaction qualities.

To prevent heaving or settling of the slab, it would also be a good idea to dowel in the new slab to the old. If you ever plan on finishing the basement or putting down flooring, I would highly recommend this to avoid future issues.
 
#6 · (Edited)


http://www.pavingexpert.com/concjnt1.htm

These dowels in the edges of the existing slab will prevent the slab from heaving or settling differently than the existing slab.

In a monolithic pour, the concrete is all unified and if any settlement occurs, it occurs as a body. Since a trench has been cut, you have essentially separated this slab, meaning that any settlement in the future may settle at different rates.

If you plan on putting down tile, carpet, or any other flooring system, or if you plan on inhabiting this space, the dowels will bond everything back together so that you don't have to worry about the new trench slab popping up or settling down.
 
#8 ·
Yup.

CA6 fill would be cheaper to be ordered from a materials company who can deliver it to your drive way. You simply need to figure out how much cubic feet of fill you need.

When they trenched the basement floor, what did they pull out under the slab? If its clean gravel, and they saved it, I don't see any reason why you wouldn't be able to reuse it.

As far as welded wire fabric (reinforcing), and rebar, both of those can be found at your local home improvement store. You will have to drill the existing slab edge for the new dowels. Place them in the drill holes loose, and then set the other end in the wet concrete.
 
#9 ·
Wow, okay awesome. The "gravel" they pulled out from the trench is mostly red/orange sand-like material, large rocks, and clubs of gravel stuck together with concrete. We still have it. It has been sitting outside for a month or two. Would you use that?

Martin
 
#10 ·
The biggest issue with the base that you use is compaction.

For instance, using a silty soil that is very organic can lead to terrible settling. A concrete slab on grade is not able to span, thus its only as strong as its base. If the base settles, the concrete will settle as well.

Sand is not a terrible base as it drains well, but doesn't compact well.

If you don't see a bunch of settlement cracks or other indications of movement of the existing slab, the base may be fine. Its a judgement call without expensive testing.
 
#15 ·
Okay, so it sounds like either I use the stuff that was in the hole and then pour concrete on top to make a level floor--pour a slab. Or I use something like this product to fill in the hole and then pour concrete on top.
That is actually grout.

Use concrete, which is a mixture of some of the ingredients in the product above with aggregate (sand and gravel).

http://www.homedepot.com/webapp/wcs...roductId=202187499&R=202187499#specifications

Depending on how many cubic feet of concrete you need, bagged mixes like this might be a pain. Then again, in a basement application, this might work well.

And the concrete slab should be about 7 inches thick, according to the drawing above?
That drawing was just to illustrate the doweling technique. Match the current slab thickness.
 
#14 ·
To be completely honest, I understand the reasoning behind the rebarb, but that sounds like over kill to me. Am I just being a newbie? I am overseeing the remodeling of this house for men and women coming home from incarceration, and I'm not certain, I know any volunteer with a huge masonry bit and the experience to use it.

Thoughts?

Martin
 
#21 ·
While the pros here are telling you the EXACT correct way to do this, do what Tarheel says a couple posts above. Use what came out of the hole, being sure to tamper it in many stages along the way.

Last I checked this was the "DIY Home Improvement Forum", not the "Professional Concrete Flooring Forum".

Thank you for offering your professional opinion, but don't get pissy when it is pointed out how much overkill it is.

OP, you can do what the experts say and be 100% you will never have a problem, over do what Tarheel says and only be 99.5% sure that you will never have a problem. It is your time and money. You make the call.

B
 
#22 ·
Remodeling a house for men and women coming home from incarceration is not a normal DIY home improvement.

The Pros giving their advise on how to do it right probably already have seen the outcome of skipping proper technique/procedure.
 
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