Construction of Mat or Raft Foundations
When would a raft foundation be used?
They spread the load imposed by a number of columns or walls over the area of foundation, and can be considered to ‘float’ on the ground as a raft floats on water. They are suitable where: Floor areas are small and structural loadings are low, such as in one or two-storey domestic construction. A basement is required.
In what situation raft foundation is provided?
Raft foundation is generally used to support structures like residential or commercial buildings where soil condition is poor, storage tanks, silos, foundations for heavy industrial equipment etc.
What is the purpose of raft foundation?
The principal aim of a raft foundation is to spread the load of the building across the entire available surface area under the building. This reduces the stress on the ground below, providing a solid foundation that can accommodate ground movement whilst still maintaining structural integrity.
Under what circumstances raft foundation is adopted?
Under what circumstances raft foundation is adopted? Raft foundation is used where settlement above highly compressible soils, by making the weight of the structure and raft approximately equal to the weight of the soil excavated.
What is the minimum depth of raft foundation?
The minimum thickness of raft foundation is 300mm.
How do you raft a foundation?
A raft foundation is constructed by first excavating the ground to a uniform, flat level. Then, a waterproof plastic sheet is laid over the earth, and a thin 3″ layer of plain cement concrete (PCC) is poured just to create a perfectly flat and level base for the foundation.
Which soil is suitable for raft foundation?
Raft foundation is preferred when the clayey soil is compact and hard. Even strap foundation can also be used. Soft clayey sand is prone to expansion and shrinkage. They have a low bearing capacity and are unsuitable for footing and strap foundation.
Is a raft foundation expensive?
Raft foundations are relatively inexpensive and fast to put down, when compared with other types of foundation. Ground excavations are less onerous than for trench excavations, for example, and the foundation and floor slab can often be combined, giving significant savings on materials and time.
What is foundation spread?
Spread foundations are foundations at shallow depths of burial where the ground resistance on the sides of the foundation does not contribute significantly to the bearing resistance. Some of the provisions in this Section may also apply to deep foundations, such as caissons and piers [C6.
What is the difference between strip and raft foundations?
Strip foundation is used to support a line of loads such as load-bearing walls. … Raft foundation consists of a concrete slab which extends over the entire loaded area so that loads from entire structure are spread over a large area leading to a reduction of the stress of foundation soils is reduced.