Monday, February 26, 2018

ADVANTAGE AND DISADVANTAGE OF RAFT FOUNDATION

Advantage of Raft Foundation

  • Raft or mat foundation is economic due to combination of foundation and floor slab.
  • Better water- proofing treatment ease of  reinforcement fabrication and laying of concrete.
  • Mat foundation is one of the most dependable solution to uneven and difficult land areas. Sometimes the soil has a low bearing capacity while other times, making individual footing is not feasible. A mat foundation is the solution to these problems.

  • The excavation required for the mat foundation is way less than what is required by other foundation. This saves resources, labor as well as money.
  • In case of soil having low bearing pressure, Ultimate Bearing capacity increases with increase width of the foundation. Settlement decreases with increase depth. The amount of differential settlement between various parts of a structure is much lower than that if the same structure was supported on individual footing. Hence, maximum total settlement which can be allowed for a particular structure is more than what is permitted when the structure is resting on individual footing.
  • Mat foundation is perfect for soil that is subjected to subsidence. For e.g. clay is a kind of soil that keeps on contracting and expanding as the temperature changes, this is why, building a structure directly on the soil can make it dangerous.
  • It reduces differential settlement.
  • The soil has a low bearing capacity so the weight of the building needs to be spread out over a large area to create a stable foundation.
  • If the walls of the building are so close that it would cause the individual footings to overlap, then raft foundations should be used.
Disadvantage of Raft Foundation

  • Mat foundation requires specific treatment for point loads.
  • Sometimes, mat foundations need heavy reinforcement in certain areas, which can add up to the price of the manufacture.
  • Sometimes, the design can become very complex and thus, requires really skillful and experienced engineers as well as workers. This can be a problem when a builder doesn’t have access to skilled workers.
  • Edge erosion occurs if not treated properly.

  • Frost can have an adverse effect on the mat formation.

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