Above Ground Pool Floor Collapse
This article is about an above ground pool that was less than two years old that suddenly developed a depression in the floor. This depression quickly worsened over the course of a few weeks time and eventually gave out which resulted in a sudden failure of the pool liner. The floor of the pool liner ripped and collapsed into a sinkhole below the pool floor. The pool, which was occupied at the time, suddenly vortexed and drained out through the new hole in the floor. The rushing water flooded the property surrounding the pool and drained into the basement of the house causing extensive damage inside the home.
This pool was less than two years old
The pool owner had reached out to the (very large) company that built the pool less than two years ago when they noticed that the floor appeared to be sinking. They were told that the depressions in the floor were normal in the spring. Follow up calls, emails and pictures were sent to the pool builder as the problem worsened, and the pool owner was told that this is all well within "normal" for an above ground pool and that they should not worry as the liner is "impervious to damage" and "will not rip" no matter how bad the depressions might look in the floor. The pool owner was told this right up until the day before the total pool failure.
The owner of this pool is pursuing an insurance claim with their home insurance for both the pool as well as the damages to their home. Is it just bad luck to have a pool failure like this with a pool less than two years old, or is this a result of poor installation? Or perhaps this is a result of slow response time from the builder responding to concerns about a developing problem from the pool owner. Or perhaps this is due to external causes such as animals or insects - it is difficult to say with certainty what caused this failure but I am certain that we can all agree that this is not normal, or acceptable, for a pool that has not even experienced two swimming seasons yet. Sure above ground pools fail all of the time, and poor craftmanship in the above ground pool market is not hard to find, but the nature of the failure of this pool is uncommon to say the least. Most likely there are a few factors at play here which all contributed, at least in some way, to the deterioration and sudden failure of this pool.
Build Quality - Upon inspection of this buttressless above ground pool it is clear that the installation was poorly done. Most specifically the straight wall on one of the long wall sections is clearly installed wrong. The pool owner stated that the wall has looked like this since it was installed, and that they had complained about this to the builder from day one however they were told that this is normal for oval pools.
You can see clearly in the picture how one upright is too far forward into the pool. This is the exact spot where the pool ended up draining out through. It could be a conincidence that this visually imperfect area is the area where the floor ended up collapsing, but it could also be a clue as to what happened to cause this relatively new pool to fail in such an unusual way.
It is important to note that this is a buttressless pool which means that there is no A-frame support holding the weight of the walls in place. On this type of pool there are braces buried in the ground (which can be seen in this picture). If the wall upright is in the incorrect place this could cause the wall to unevenly distribute the forces acting on them. While I consider this wall to be a fairly significant installer error, I do not see how it directly was the cause of the sudden pool floor failure.
Floor Material - The floor material used to create the smooth bottom in this above ground pool was compacted peat moss. This is not something that I have ever used for a pool base, nor have I heard of any company using this for a pool base. The peat looked to be about 1.5" in thickness or so in most places, and it was put right over existing soil and roots.
Roots From Adjacent Tree - There is a huge tree stump located less than ten feet from the side of the pool wall (on the opposite side from where the pool floor collapsed). This stump measures almost four feet in diameter, so the tree was extremely large before it fell in a wind storm onto the above ground pool that was located on this property before the one that is there now. The old pool had a tree fall on it, and less than two years later the floor collapsed in this pool. This pool owner has terrible luck!
The Hole - The hole in the floor actually appears to be two holes, with the possibility of more that are yet undiscovered. The main hole measures about 24" across, but also has a depth of around 24" which is incredibly deep. A second hole directly next to but not connected to the first is about half this size and half the depth. As the pool drained it surely washed away some of this dirt which makes the holes even larger, but the holes were already deep enough to cause the floor to collapse and the liner to suddenly rip. It is worth noting that the pool owner was present when the failure happened (they were actually in the pool at the time), and they used the handle from a rake to push down through the hole to see how deep the hole was. At this time they were able to effortlessly insert the entire length of the rake handle straight down through the floor of the pool which indicates that the ground was significantly saturated and destabilized.
Of course the pool company is taking no blame for this problem. The pool is over one year old so there is no warranty left on it, and despite the fact that the pool owner had made them aware of the worsening problem, they do not feel like this is their problem and made no effort to inspect or repair the problem. The pool company is now no longer communicating with the pool owner and the pool owner is left with a destroyed backyard and flooded house due to a pool that they paid over $10,000 for less than two years prior.
What Caused This Pool To Fail?
The way in which this pool failed is odd. For holes this large to appear an within a very short period of time and cause a total pool failure is crazy. What really shocked me is the cavernous size of these holes. My initial impression is that a long term leak must have eroded the soil in this location. Since there is no sand used for the construction of this pool floor, the dirt and peat moss easily washed away with the flow of moving water, much faster and more aggresively than if the floor was made from heavier aggregates. As the water leaked in this spot the hole got larger until eventually the liner split, probably on a sharp rock or root in the ground (or possibly from the buried metal brace).
I considered burrowing animals like chipmunks and gophers being the cause of this, as well as ground dwelling hornets which are common in the area where this pool is located. After inspecting the pool I did not see any evidence that would point me towards thinking that this was the cause of the failure. There were plenty of hornets occupying the hole when I inspected this pool, but I think these were more taking advantage of a good situation for them with these giant holes conveniently in the ground for them to explore. I also considered the poor installation quality and the misplaced support upright, but similarly can draw no direct causation from this installation error in relation to the pool floor collapse. Also worth considering is that the system of roots which exists below the pool floor could be decaying since the tree fell and had to be cut off at the trunk. The tree was massive, and as such there could easily be a massive root network that has begun to rot. This could result in large pockets of unstable dirt directly below the pool which also could account (at least in part) for this pool failure.
Expert Input Needed - If you are a pool professional and you have some ideas as to what caused this failure to happen, please add a comment in the section below, or email Steve if you would like to share your ideas on this page.
For further information you can check out the next installment in this story with this pool sinkhole part 2 follow up article.
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