There are two basic types of foundations. Open foundations and Pile foundations. Whenever open pits are done prior to the footings, these are known as the open foundations. But when there is a boring done in the earth, reinforcement cage is lowered and casting is done, this is known as the Pile Foundations.
When the hard strata /subsoil is at a deeper level, more than 8’, it becomes practically difficult to carry out the open footings due to the following reasons:
- Cost of bailing out of the soil becomes excessive.
- In case of the subsoil water, the dewatering becomes an extra activity to be managed.
- In deeper excavations, the stability of the excavated pit is not reliable. The excavated pit might collapse and may thus endanger the people working underneath.
- The substrata may not be strong so as to support the open footings. It may comprise of heterogeneous soil mixture, filled up layers, marshy soils or water logged soils etc.
Also go through the following articles for more clarity :