Shallow foundations – commercial
A shallow foundation transfers loads from a building into the upper layers of the ground rather than to a deeper soil or stratum like a deep foundation. In commercial buildings, shallow foundations are commonly combined with ground-improvement techniques to increase the bearing strength of the soil below the foundation.
A mat foundation, often referred to as a raft foundation, is a variety of heavily reinforced slab-on-ground foundation that is used to distribute large structural and seismic loads across a wide area. Mat foundations can be constructed near the surface or well below ground, depending on the size of the building. In either case, the mat foundation spreads the load over the soil beneath.
In commercial buildings, mat foundations often involve deep excavations and large amounts of concrete and steel reinforcing. In high-rise buildings, these kinds of foundations can be several metres thick with extensive reinforcing that must be specially designed and installed to ensure loads are evenly transferred to the ground.
A floating foundation is a special type of mat foundation where the weight of the soil excavated is equal to the total weight of the building. The structure does not add any further load on the underlying soil and is therefore not likely to settle over time. In practice, some settlement can occur in earthquakes if the ground beneath liquefies or if ground water levels reduce for some reason within the land surrounding the site.