Pouring concrete or paving on sand is an exercise in faith. These triangle cracks are typical of concrete failure.
The entire coast of Georgia is basically sand. They pave the roads here and within a year or so they are like roller coasters - you go up and down and up and down. Things just sink in, and it is a way of life. Sadly, this means sidewalks, driveways, and even foundations of houses can sink and settle and there isn't too much you can do about it.
When we moved to Jekyll Island, our sidewalk leading from the driveway to the front door was pretty level. But within a few years, it started to settle oddly. There was one crack in one slab, and another slab jutted up so that it made a 2" high gap that people tended to trip over. Our insurance company would no doubt not be amused.
You see this all the time in public settings - someone goes around with spray paint and marks the uneven gaps in the slabs. Then, later on, sometimes they bring in a grinding machine to grind the slabs so they are even and no one trips. Sounds expensive, but all it takes is one personal injury suit and you are paying a lot more. We are a litigious society. Then again, falling down, particularly when you are old, is no laughing matter.
I saw our postal lady almost trip on the sidewalk and decided I better do something about it. The way most people deal with this is to jackhammer up the entire sidewalk or a substantial portion of it, and the pour a new slab. I didn't want to spend all that dough, so I got a long 4x4 that I had laying around and wedged it under the slab and using another shorter 4x4 as a pivot point, leaned on the longer board and the sidewalk levitated up 2" or more. I jammed some old bricks underneath it and then got a wheelbarrow load of dirt and wedged it under the slab, using my 4x4 to tamp it in place.
Well, that was nearly a decade ago, and the sidewalk has yet to settle again. I am sure it will, though. Like I said, paving sand is an exercise in faith.
Recently, I noticed that the side door to Mark's studio was having a hard time closing, or at least the storm door was. I looked at it and realized the door opening was a parallelogram, and not square. What's up with that? I realized that the small side porch (10' x 4') off the side door was poured on a separate slab, and that one end of the slab had settled three inches or so, causing the other end up move up about an inch, pinching the door frame in the process.
I tried the 4x4 trick, but realized a hydraulic jack would work better. I dug under the slab, which wasn't hard to do as the soil under that end had eroded a bit underneath (hence the settling). I jacked it up and as I did, the other end went down and the door frame unbent itself. I could close the door without kicking it! I jammed some bricks underneath and then packed underneath with soil, again using my trusty 4x4 as a battering ram. It was messy and laborious work to say the least. I then piled soil around the slab, so the erosion thing would not occur again - at least not soon.
That was the problem with that slab - and my sidewalk. The ground next to both slabs was much lower than the slab itself, so that over time, the sand under the slab migrated away, leaving a gap underneath. With no support, the slab settles over time.
The photo above is a typical failure mode I see all the time in driveways and sidewalks - a "triangle" fracture at a joint seam. Expansion joints are molded or cut into concrete slabs to allow the slabs to move over time. But the soil under the corners sometimes erodes, mostly because rainwater trickles down through those expansion joints (which should be sealed, actually). The soil under the corner erodes and someone drives a heavy vehicle over the slab and it cracks.
We see this all the time on our bike path - there is a storm and the authority drives a truck over the bike path to clear out fallen trees. They end up cracking the slab, usually in these triangular corner pieces about 1-2 feet across. Sometimes they cut it into a neat triangle and pour new concrete. Other times, not.
I see this all the time on driveways, including our own. Sadly, older driveways will do this, once the soil under the slab erodes. People blame the delivery truck driver for "breaking their driveway" which is why the FedEx and UPS guy now park in the street with their flashers on, blocking traffic. But it isn't the truck that breaks the driveway, it is the erosion of the soil underneath.
Our driveway wasn't in the best of shape to begin with. We had one really bad portion hammered up and replaced. The remainder has a lot of cracks. When we had two 100-foot pine trees removed, they had to crane them over the house, and this meant putting a crane in the front yard. The crane operator said, "We can do this, but it will likely crack your driveway." We had to agree to this, otherwise the trees weren't coming down. And they kept their word - the driveway cracked - in several places more than it was before.
After my success with the sidewalk and the porch on Mark's studio, I thought I could try the same technique on the driveway. It is a lot harder to do, however. There are people who do this for a living, and they actually drill holes in the concrete, inject an expanding foam underneath, and raise the slabs so they are level again, and then seal the cracks. It is pretty slick, but not cheap, of course. The only other alternative is to jackhammer the whole thing up and start over. And that is what we will have to do, as our driveway is now more cracks than concrete.
But I gave it a try and realized why my concrete man said it wouldn't work. While I could pull up the offending triangular pieces and put new soil underneath (and pack it down), replacing the pieces wasn't like doing a jigsaw puzzle. They were shaped such that you couldn't just slide them into place as they had complicated edges. They never quite go back all the way - which is why many people cut the offending section into a smooth triangle and pour new concrete in, instead.
(The foam thing would have worked several years ago, but by now, our driveway is shattered into so many small pieces this technique wouldn't work).
Still, I was able to level up one section and it doesn't look too bad, but eventually, we will have to budget for a new driveway. And a new roof. And new kitchen appliances. And new plumbing. And a new tile floor in the kitchen. And new faucets. The shit never ends, which is why I don't understand why people are so ga-ga about houses and why people today are paying boatloads of money for them. Even a house in "perfect" condition will need major rehab in as little as ten years.
Removing the broken portions, I realized another reason why the slab broke - it had no rebar. Well, it had rebar, but it wasn't in the slab. Whoever poured the driveway laid the rebar grid on the ground and then poured on top of it. The rebar grid did not penetrate the concrete all the way and was, in fact, in the sand underneath. So it rusted away and wasn't providing any tensile strength. In fact, it was so rusted I could break it off with my hands.
We always had asphalt driveways in Virginia and New York. I am not sure why they are not popular in the South, other than maybe the heat? In New York, we had one hell of a driveway put in - they dug down two feet, poured gravel, rolled it, poured gravel, rolled it again, and then did a rough layer of asphalt one year, let it sit for a season and then a fine layer on top - and then sealed that a year later. The people we sold the house to no doubt enjoyed it. Smart people - they rent out the studio in the barn as an Air BnB!
But I digress.
There are things you can do, as a homeowner, to prevent this from happening or at least slow the process. First, if you have gaps in the concrete at expansion joints, look into getting some self-leveling caulk or gap sealer and pour in the cracks. You may need to put a foam "biscuit" in the crack or otherwise you'll just dump an entire tube of caulk in there. Sealing those gaps will prevent water from running in and eroding the soil underneath.
Second, if your slab is noticeably higher than the surrounding ground, you might want to mound up some soil alongside the slab. I plan on doing this around Mark's studio, as there are parts where you can see under the slab as the soil has eroded away. I plan on jamming some soil under there first, with a 2x4 or 4x4 and then raising the soil level around the slab, so the sand underneath doesn't migrate away. Sand and soil will seek its own level over time, and there isn't much you can do about that, other than to prevent water from accelerating the process (by sealing the gaps) and not giving the sand an exit strategy from underneath your slab.
You could, I suppose, prevent big trucks from parking on your driveway, but that isn't really a workable solution. The problem isn't the trucks, but the erosion underneath. We have a neighbor who got into a tiff with their roofer. They had a pallet of shingles delivered to re-roof the house and the flatbed truck punched a neat 2'x2' hole in the driveway nearly a foot deep. They blamed the roofer, who agreed to pay for "the damage" but the real problem was the foot-deep hole underneath the slab which gave no support to the concrete above. I suspect they will have similar problems down the road when other parts of the slab collapse. Like I said, this is why the delivery people are parking in the street these days (that and they hate backing out of driveways).
Owning a home is owning an expensive machine for living. It sounds like fun and all, but it gets expensive over time. I am hoping to keep the driveway patched together for a few more years until this crazy economy cools off. My concrete repair guy who I used in the past to pour some sidewalks around the garage, tells me that he is slammed with work and is booked until 2023. My neighbors who have a hole in their driveway got the roofing company to agree to pay for "repairs" but they can't find anyone who will do the job in the next six months, at least!
So today is a good time to patch, a bad time to replace.