One of the most uncertain parts of building an inground pool, is digging the hole. The machine used is the muscle, and that of itself is not difficult, but what lies beneath the surface is often reason for concern.
We cannot control what we cannot see underground. Usually, if we encounter a problem digging, it will not be in the first couple of feet. Once we reach depths greater than three or four feet is when we can we see a potential problem unfolding.
Underground surface conditions that are of concern are garbage, construction debris, abandoned structures or utilities, water, bedrock, sand, or unstable soil conditions. These can lead to design changes, additional construction techniques, and modifications to the structural integrity of the vessel. A good design and engineering team will be able to walk you through the possible options available and work out the most cost effective and viable solution.
Make sure your pool contractor has provisions in the contract for such conditions. Even if you have to deal with such unfortunate conditions it will be helpful to understand what to expect from your contractor. Any new work or adjustments to the original contract should be documented and signed by both parties.