Throughout the United States there are different topographies and landscapes. When building an inground pool an installer must take this into consideration. The different soils can cause for different materials to be used. During excavation there might be water problems wherein the water table is too high. The excavator can stop and dig a small hole and place a sump pump in the hole while getting rid of the problematic water. To protect the liner and also to create a nice smooth bottom the installer will mix a base to go underneath the liner and on top of the soil.
With a high water table the recommended 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.
When building an in ground 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.