For example, if you have a high water table the recommended pool base would be a mixture of vermiculite. It is a form of concrete that has more porosity than regular concrete. It is flexible and when the water pressure builds up, the concrete will flex with the pressure and therefore not crack and push the water back down, protecting the liner.
Another example is when building an inground pool on an incline or next to mountains, it is recommended that a retaining wall be placed to help with the hill slope. There are different types of braces for different types of areas. For the hill slope areas there is an X-brace with a deck support which helps keep the pool level as well as the deck which is to be poured after the pool is finished. The deck support is a good option when using bricks or stones around the deck if a concrete deck will adjoin the brick or stone coping. If braces are not used, then the weight of the hill slope can push on the deck and cause it to push the wall of the pool. The deck is usually installed on at slope that way water can runoff onto the landscape.