What is a raft foundation slab?

A raft foundation is a reinforced concrete slab under the whole of a building or extension, ‘floating’ on the ground as a raft floats on water. This type of foundation spreads the load of the building over a larger area than other foundations, lowering the pressure on the ground.

How deep does a raft foundation need to be?

Raft foundations (sometimes referred to as raft footings or mat foundations) are formed by reinforced concrete slabs of uniform thickness (typically 150 mm to 300 mm) that cover a wide area, often the entire footprint of a building.

What are the three types of raft foundation?

There are five main types of raft foundation:

Solid slab rafts,
Slab beam rafts,
Cellular rafts,
Piled raft foundations; and,
Balancing (or floating) rafts.

Are raft foundations good?

A raft foundation spreads the weight of the building over the whole ground floor area of that building. Rafts are most suitable when the ground is of good load bearing capacity and little work is required to get a solid foundation.

Why raft foundation is required?

A raft foundation is often used when the soil is weak, as it distributes the weight of the building over the entire area of the building, and not over smaller zones (like individual footings) or at individual points (like pile foundations). This reduces the stress on the soil.

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 the cheapest form of foundation?

Concrete Slab
Concrete Slab Cost Concrete slabs are generally the cheapest type of foundation to install. Because they’re built slab-on-grade, they don’t require much excavating or ongoing maintenance, and they typically don’t promote moisture problems.

Where do we use raft foundation?

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 are the disadvantages of a raft foundation?

Disadvantages of Raft Foundation

Raft foundation is prone to edge erosion.
Raft foundation requires more amount of reinforcement in some cases, and it will ultimately cost more.
Skilled labours are required as compared to other foundation.

What are the different types of raft foundations?

Types of raft foundation include: Solid slab raft, sometimes referred to as a plain raft, and including; flat rafts, mats, wide toe rafts, slip plane rafts, blanket rafts, and so on. Slab beam raft. Cellular raft.

When do you call a slab a raft foundation?

When more than one (1) line of columns is supported by a concrete slab, The it’s referred to as a raft foundation. also calculation mat calculation/ Raft calculation Combined footings could be classified generally under the following categories: (Types of Raft Foundation)

When is the raft foundation supported on piles?

When the raft foundation is supported on piles, it is called a piled raft. In this article, you’ll learn all about Raft or Mat Foundation, Types of Raft Foundation, its Design, etc. in details.

What’s the maximum settlement for a raft foundation?

And also due to the stiffening effect of the raft and building frame. Due to continuity and negative moments, the bending moments produced in rafts tend to be less. Thus, an allowable maximum settlement of 50 mm is usually specified for raft foundations.

What is a raft foundation slab? A raft foundation is a reinforced concrete slab under the whole of a building or extension, ‘floating’ on the ground as a raft floats on water. This type of foundation spreads the load of the building over a larger area than other foundations, lowering the pressure on the ground.…