Raft foundations are used for all of the above.
A raft foundation is a type of foundation that spreads the load of a structure over a large area. This is done by creating a concrete slab that is supported by the soil below. Raft foundations are often used in areas with poor soil conditions, as they can provide a more stable base for a structure than other types of foundations.
Raft foundations can also be used to span over small soft or loose pockets in the soil. This is because the concrete slab of a raft foundation is able to distribute the load of the structure over a larger area, which can help to prevent the structure from sinking into the soft soil.
Finally, raft foundations can be used to counteract the hydrostatic effect. This is the upward force that is exerted by water on a structure. Raft foundations are able to resist this force by spreading the load of the structure over a large area.
In conclusion, raft foundations are used for all of the above: providing increased area of foundation over poor bearing capacity of soil, spanning over small soft or loose pockets, and counteracting the hydrostatic effect.