How Foundations Work & Why They Are Important
A foundation is indispensable for the structure and stability of a building. The function of the foundation is to transfer the weight of the building across the ground beneath it. Foundations come in all shapes and sizes but are mainly distinguished as shallow or deep foundations. Soil and rock mechanics can be manipulated in order to create more solid foundations.
Basic Historic Foundations
The simplest form of foundation is the Padstone. A padstone is a single rock that spreads the weight onto the ground whilst also raising the structure, usually wooden, off of the ground. Padstones are only viable for small, light-weight structures. Another foundation that uses rocks is the Ston Foundation. Stone foundations are a combination of dried stones and stones that have been laid in mortar. Gabions, a cylinder filled with rocks and concrete, can also be used to add additional strength. Shallow trenches filled with rubble were probably the most common and successful foundation techniques due to their ability to hold extremely heavy structures in complimentary soils. These foundations can be regularly spotted at archeological digs such of those featured on Time Team.
Modern Foundations differ depending on both the soil and the building type. Soil capacity is determined via the use of Terzaghi’s Bearing Capacity theory. You can read more about this theory here in an article that we posted a week ago. If the building is lightweight then the most common foundation would be a footing foundation. A footing foundation is embedded between 90 and 120cm into the ground so that it reaches beyond the frost line. Footing foundations can also use a technique to spread the weight of structure over the proximate soil. This ‘Spread Footing’ technique uses reinforced mat slabs which are a quarter of a meter thick. Deep foundations are required when the top soil is weak and low density. The deep foundations are built through the weak layer into the deeper, stronger soil. This soil is able to have a greater bearing capacity. There are many different techniques for deep foundations including but not limited to; Piles driven into the ground, drilled shafts, helical piles, and caissons.
This video provides you with a more detailed description of Shallow and Deep Foundations and some of the pros and cons it will also help you better understand how foundations work: