Garage Slab Has Settled 6 inches 9

[cap4000]

I just inspected a residence and the garage slab has settled 6 inches in the center of garage in a V-like shape. When the car is parked the bearing pressure and deflection coinicide at the centerline. Has anyone ever seen a 6 inch deflection? Any tips will be greatly appreciated.

 

[fattdad]

yes. I've seen post-construction settlement over 12 inches. Typically it's from improperly compacted fill.

f-d

¡papá gordo ain’t no madre flaca!

 

[PSlem]

See a lot of them with non-structural double garage slab on basement lot. Tear out, add a couple helical piles in center and do a structural slab.

 

[msquared48]

Makes me wonder about the footings for the rest of the structure and what they rest on.

Mike McCann
MMC Engineering

 

[MiketheEngineer]

fattdad is right -

I have seen this many times and usually caused by no or non compacted fill.

Tear it out and do it right

 

[MiketheEngineer]

Second thought - you could probably have it mud jacked.... but sort of like putting gum on a break.

Might work - might not.

 

[Ron]

Based on the pattern you described and considering that you did not mention distress anywhere else in the structure, it is likely that the slab was built over a bunch of buried debris, a large tree stump or there is a pipe below that has raveled the soil.

Check all before deciding on a fix...

 

[aeoliantexan]

I agree, uncompacted fill is most commonly involved. With the maximum settlement in the middle of the garage and the perimeter OK, one could suspect that the contractor dug a hole and buried trash before pouring the floor.

Loose fill will often support light pressure such as a floor slab so long as it does not get wet. Saturation leads to much settlement. Look for a water source such as poor exterior drainage or a broken pipe. Perhaps the poor fill has a wider extent but the broken pipe has only affected a limited area - so far.

Another possible cause would be a natural sinkhole if the house is in a karstic area.

 

[concretemasonry]

In some residential construction, the basement or attached garage is a "floating" slab that actually bears on the top of the strip footings and also does provide some lateral resistance to the walls bearing on a strip footing.

Unfortunately, the slab is one of the last horizontal surfaces poured (basement is second from the last to permit utilities, etc.) in the construction sequence. All debris ends up in the garage slab area aand there is no control. In one day the rest of the area can be filled, leveled, compacted in some manner(if you can compact drywall and 2x4 stubs) and the sidewalks and driveway poured in one day as the contractor works away from the residence. - Next is grading and grass.

I currently live in a 30 year old quad home (each unit is 1/4 of a two story rectangle) and 1/2 of the garage floor is severely cracked and settled somewhat. I saw it when I bought and knew the process. My neighbor had his repaired and 1/2 of the garage was perfect, but they just cut the slab in 1/2 and excavated the area possible. The excavated material revealed a history of the scraps thrown away, but the other 1/2 was almost too difficult to comprehend excavating.

I think aeoliantexan has the most likely source as being construction debris buried under the slab. There is usually no inspection or controls over the finishing of a project that can be completed so fast. - That is possibly why they are still looking for Jimmy Hoffa.

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[RFreund]

What about a cracked pipe below creating some sort of sink hole? The settlement is very isolated, right?

EIT

 

[RFreund]

should have read all the posts first....

EIT