As per Technical Norms, This type of foundation called as Solid Base Raft foundation or Continuous Raft or Mat foundations.
A raft foundation, also called a mat foundation, is essentially a continuous slab resting on the soil that extends over the entire footprint of the building, thereby supporting the building and transferring its weight to the ground.
A raft foundation is often used when the soil is weak, as it distributes the weight of the building over the entire area of the building, and not over smaller zones (like individual footings) or at individual points (like Group Pile foundation). This reduces the stress on the soil.
A raft foundation is also very good for basements. Foundations are created by excavating soil in order to find strong, compact, undisturbed natural soil that is at least a few feet below ground level. This soil is much stronger than the loose soil at the surface. If we construct a raft foundation at say 10 feet below ground, and build concrete walls around the periphery, this makes an excellent basement. Therefore, an engineer designing a building with a basement will tend to choose a raft foundation over other types of foundations.
From the picture shown it is not clear to see the proper foundation, but what it seems to be is raft foundation, here the coloumns of structure are sharing a common base and connected to each other with beams at the base. Raft foundation is used in places where bearing capacity of soil is less than desired load bearing capacity