no dirt under concrete slab?

[Bigbartguy]

hi folks

I've got a big gap under my concrete sidewalk (i.e. no dirt under the concrete)...the gap is probably 2 inch deep x 12 inch wide and extends almost 2-3ft under the slab. I can jam a broomstick all over underneath the slab.

I'm worried that this concrete will end up breaking since there is no support in this area. It hasnt sagged or broken yet, but I expect it probably will.

how can I build the area under the slab back up? do I need to mudjack it?

incidentally, we discovered the gap when we were tearing out a bush and THIS thing just about gave my wife a heart attack:

[TruthWalleyes]

Dig out around it, fill it in with gravel.

[soldoncass]

I lot of times just dirt pushed under there with a 2x4 and compacted will solve the problem. The times it WON'T is when water is washing it out, so check the landscaping grade. In that case you may need some sakrete pushed under there to make it permanent, but make sure water runs AWAY FROM there ,instead of TOWARD IT. As far as the sidewalk breaking up.....as long as you don't drive on it, it will take a lot .

[TruthWalleyes]

DOn't replace the missing dirt with more dirt...There shouldn't be dirt there in the first place. Gravel.

[soldoncass]

If the reason it is gone is from washout, like it normally is, gravel WON'T SOLVE the problem. Don't put black topsoil under there, but something that compacts. #1 problem is the water problem, fix that, then sakrete concrete mix makes the repair pernanent.

[pureinsanity]

Nice bull snake. There should be no dirt under your side walk. if there is they didn't base it correctly. I would replace it with class 5 gravel and pack it in with a shovel handle or piece of wood like suggested. Check your grade and see what caused it to wash out and correct the problem so it doesn't happen again. The biggest concern is if water gets under it and freezes and causes it to heave.

[SpclPatrolGroup]

You can have someone come and sand jack it, basically they put a hose under there and pump in sand, its really the only way to do it and get good compaction. We see this a lot, concrete company gets lazy and either dont use enough class 5 or compact it enough before pouring.