Home driveway question
Home driveway question
(OP)
I need an expert's advice on my home driveway situation. My sewer drain pipe runs under the concrete driveway. After failing to remove the blockage in the sewer pipe, he is going to cut a hole in the driveway and do the necessary repair. He recommends a new driveway afterward. This is why. My concrete driveway is cracked into several large pieces (25 year old house). One piece is noticeably sunk. According to my plumber, the piece sank under vehicle load, moving the soil underneath, which in turn damaged the sewer pipe.
Here is my question. Did the sinking concrete move the soil underneath? Or did uneven settling of soil cause concrete pad cracking and sinking? If the former, I will need to get a new driveway. If the latter, I may not need a new one.
I live in Dallas. We have an expanding clay soil. As it goes through dry/wet periods, it can cause structural damage to homes, they say. Thank you.
Here is my question. Did the sinking concrete move the soil underneath? Or did uneven settling of soil cause concrete pad cracking and sinking? If the former, I will need to get a new driveway. If the latter, I may not need a new one.
I live in Dallas. We have an expanding clay soil. As it goes through dry/wet periods, it can cause structural damage to homes, they say. Thank you.
RE: Home driveway question
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Home driveway question
Most likely shrinkage cracks occurred in your slabs long ago. As time progressed the cracks widened. As they did so, they lost a lot if not all of their load transfer capability as wheels roll across the crack. This causes the slab to deflect differentially under the load. It also allows more water to get into the underlying soil. Both of these can cause soil displacement and depending on the depth of the pipe, can damage the pipe.
I would recommend replacing the driveway, making sure that properly spaced control joints are cut the same day as concrete placement. The contractor will balk at this but make him do it.
The slab should be consistent in thickness with a minimum thickness of 6 inches. The tolerance should be -1/4 inch, +3/8 inch. Wet cure the concrete for 7 or more days before putting load on it. Use 4000 psi concrete. You need the durability of the stronger concrete. Lower strength will do for the loading but will be less durable.
RE: Home driveway question
www.PeirceEngineering.com
RE: Home driveway question
RE: Home driveway question
I think it is time to let go the old drive way, and provide a new. The linked paper discuss the design and construction of pavement over expansive clay. It's worth reading and take notes. Link
RE: Home driveway question
You'll want good new embankment or subbase material (at least 6" if you're doing a 6" slab) to help mitigate some of the expansive clays issue. 4000 PSI concrete is likely good; we use a 4500 PSI standard for concrete pavement on our highways in CO but I don't think you need the same strength. Could consider tooled joints versus sawn joints (tooled grooves 1/4 slab depth deep x 1/8" wide) without any expansion joints if the driveway is shorter than a couple hundred feet.
RE: Home driveway question
Rod Smith, P.E., The artist formerly known as HotRod10
RE: Home driveway question
The performance of the driveway (or any slab on grade) is very dependent on the subgrade preparation. In residential construction it is very common for driveways to move and crack due to poor subgrade preparation, expanding soils just compound this problem. Residential driveways and slabs on grade are usually unreinforced or minimally reinforced, so they will not bridge and distribute loads over any soft spots in the subgrade. All of this will lead to cracking and settlement you are seeing.
How deep below your driveway is the sewer pipe? Is it right below the concrete so it is depending on the driveway to essentially "bridge" over it? Has soil started eroding under the concrete due to water infiltration (from rain or a broken sewer pipe)?
If the cracks don't bother you and water infiltration has not been an issue, I see no reason to replace the entire driveway. I would still recommend sealing all of the cracks to help prevent moisture intrusion under the slab.
Ron, do you see contractors having issues with this and not doing it in your area? I would be quickly finding a new contractor if this were an issue for them in my area.
RE: Home driveway question
RE: Home driveway question
RE: Home driveway question
RE: Home driveway question
Rod Smith, P.E., The artist formerly known as HotRod10
RE: Home driveway question
RE: Home driveway question
RE: Home driveway question
RE: Home driveway question
In my case, I have a well-compacted in-situ sand-gravel base that I planned on keeping undisturbed, in a location inaccessible to anything larger than a full-sized pickup. I considered a 4" slab with carefully placed reinforcing mesh, and probably poly fiber, as well for cheap insurance (local ready-mix suppliers charge $10/CY to add fibers).
Rod Smith, P.E., The artist formerly known as HotRod10
RE: Home driveway question
RE: Home driveway question
OG...this might be a first....I disagree with you. I don't consider fiber in concrete, whether steel, glass or polypropylene, to be "reinforcement". Fiber is a mix enhancement that may increase compressive and tensile strength properties of the concrete, but doesn't truly reinforce it in the same manner as rebar or welded wire fabric.
RE: Home driveway question
Any attempt at "reinforcement" is better than none. For a case where normally none is needed, BUT the site is crummy, it is an easy way to improve things. I can only Point to my limited observations of a few such uses where I'd expect cracks and faulted sections to be plenty, and there are NONE.
RE: Home driveway question
I agree, but when properly placed and supported, it does its job quite well. Without proper support, bars end up on the ground instead of in the slab, too. QC is important either way.
In my case, I plan on setting the mesh myself, so it will be, and will stay, right where it's supposed to be.
Rod Smith, P.E., The artist formerly known as HotRod10
RE: Home driveway question
My glass has a v/c ratio of 0.5
Maybe the tyranny of Murphy is the penalty for hubris. - http://xkcd.com/319/
RE: Home driveway question
For heavy use slabs/pavements where the concrete needs some flexural capacity beyond it's modulus of rupture, you need continuous bars whether you have fiber or not.
RE: Home driveway question
Rod Smith, P.E., The artist formerly known as HotRod10
RE: Home driveway question
To be clear, I agree they don't add to the strength - I also don't think they reduce flexural cracks.
RE: Home driveway question
Rod Smith, P.E., The artist formerly known as HotRod10
RE: Home driveway question
RE: Home driveway question
RE: Home driveway question
RE: Home driveway question
Good luck.
oldinspector
RE: Home driveway question
RE: Home driveway question
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm