In this article, we will discuss
Definition of Foundation | Different Types of Foundations | What is Mat/Raft foundation | Materials used to Build Raft Foundations | Mat Foundation Uses
Definition of Foundation
The foundation is the lowest part of a building that is in direct contact with the ground. It is what a building rests on or stands on. It is the foundation of groundwork, which moves the weight of the building to the soil.The ground where the foundation will be built must be strong enough to hold up the building. So, we can say that the foundation is one of the most important parts when building anything anywhere. The ground on which it will be built is called the foundation bed. Without a strong foundation bed or one that works with the soil, a building is likely to fall down, especially during natural disasters like an earthquake.
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| Mat Slab Foundation | Drainage Mat for Foundation Wall |
Different Types of Foundations
Here are some of the different types of foundations used in building:1. Shallow foundation
- Individual footing or isolated footing
- Combined footing
- Strip foundation
- Raft or mat foundation
2. Deep Foundation
- Pile foundation
- Drilled Shafts or caissons
What is Mat/Raft Foundation
It is an appropriate solution for low bearing capacity soil, spread footing cover covering approximately 70% of the structure, high structure loads, soft pockets or cavities in the soil to an unknown extent raft, and highly compressible soil that extends to a great depth.
Different Types of Mat Foundation
There are different types of Raft/Mat foundations that can be used depending on how the soil is and how much weight is being put on the foundation.Here are the different kinds of foundations used to build rafts:
- Plate mat with a flat surface
- The plate got thicker under the columns
- Two-way slab and beam Raft
- Plate raft supported by pedestals
- Plied rafting
- Cellular Raft Foundation or Rigid Frame Mat
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| Types of Mat Foundation |
a. Plate mat with a flat surface
This is the simplest way to build a raft's base. This kind of mat is used when the columns and walls are evenly spaced and the loads are small. Reinforcement is put in both directions, and there needs to be more reinforcement where the columns and load-bearing walls are. Most of the time, for economic reasons, the thickness of this type of raft foundation is kept under 300mm. A slab that was thicker would not be cost-effective.
b. The plate got thicker under the columns
When the columns and load-bearing walls have to hold more weight, the slab is made thicker under the columns and walls, and diagonal shear and negative reinforcement are stopped by adding more reinforcement.
c. Two-way Beam and Slab
In this type of raft, the beams are made all at once, and the raft slab connects the walls and columns. This kind of raft works well when the columns are farther apart and the loads on the columns change.
d. Plate raft supported by pedestals
In this kind of mat, there is a pedestal at the bottom of each column. This kind of foundation serves the same purpose as a flat plate that is thickened under columns.
e. Piled Raft
The piles hold up this type of raft foundation. When the soil is very soft near the surface and the water table is high, a piled raft is used. The pile under the raft helps to keep it from sinking and fights against buoyancy.
f. Foundation for Rigid Frame Mat or Cellular Raft
In this kind of raft, the walls of the foundation serve as a deep beam. A rigid frame mat is used when the columns support very heavy loads and the depth of the connecting beams is more than 90cm. Here, two concrete slabs are stacked on top of each other and connected to the foundation walls on both sides. This makes a cellular raft foundation. This kind of raft is very strong and cheap when the slab thickness needs to be very high.
Materials Used to Build Raft Foundations
The following are some materials used in the construction of a raft foundation:- Formwork
- Spacer
- Reinforcement
- Concrete
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Mat Foundation Functions
- Move loads from the superstructure and spread them out over the whole building footprint.
- Reduce the amount of uneven settlement in buildings built on weak soil.
Mat Foundation Uses
- It is used to build buildings that are used for business. Most of the time, the loads in this case are big. In places where basements are common, mat foundations are often used.
- Mat foundations are also used on low-capacity soil to spread out the weight of a building and make a stable base.
- It is used to stop buildings from settling in different ways.
- When the soil layer is not stable, a raft or mat foundation is used. In this case, a strip foundation would cover more than 70% of the ground area under the building.
- There are also times when the soil layer moves, which often happens in mining areas.
Construction of Foundations Made of Mats or Rafts
- Take out the dirt and dig up the soil until it is flat and even.
- Then, ramming is used to pack down the foundation bed.
- The earth is then covered with a sheet of plastic that won't leak.
- Then, pour a layer of plain cement concrete about 7 cm thick to make a perfectly flat and level base for the foundation.
- Place spacers with reinforcement on top of the foundation bed. Steel mesh is used to add reinforcements in both directions. At the top and bottom of the foundation, there are two meshes that are strengthened to even out the forces of bending up and down.
- After all the steel is in place, concrete is poured to the desired thickness. For small buildings, this is usually between 200mm and 300mm, but it can be much thicker if it needs to hold a lot of weight. A rebar cover of at least 50 mm should be kept.
- Lastly, the right curing process should be used to make sure that the concrete has the right compression strength.
Drainage mat for foundation wall
Air sealing is critical. The junction of concrete foundations and wood framing is prone to air leaks and moisture issues. Wood is frequently warped, and concrete is never flat. There are at least three places for air to enter, and there are probably many more. Leaky connections can cause issues with energy, moisture, comfort, and IAQ. When possible, extending the wall sheathing past these connections is a good first step. Caulks, adhesives, spray foam, and gaskets can effectively seal them.Unless you live in the desert, the ground is always wet, and groundwater is constantly invading. Footing drains can remove large amounts of groundwater, but foundations must also disrupt capillarity. If you allow it, water in the soil will wick all the way up to the roof framing. Capillary breaks, such as brush-on damp-proofing, sill sealer, and rigid insulation, prevent this process from taking place. Cutting corners on the foundation is a bad idea because problems are expensive and difficult to fix after the house is built.
Mat slab foundation
In building, the mat foundation is also known as the raft foundation. It is used in places where the soil can't hold a lot of weight. This kind of foundation is like a wide slab that goes on and on.This kind of base is used as the base for the whole building. Because it has to carry all of the structure's columns and beams. It is usually made to support the weight of the building's structure when the ground is weak.
The mat foundation takes all of the weight of the building's upper part and spreads it out over the ground. Most of the time, a mat foundation is a single, thick slab that is laid on the ground and on which all the building's columns and beams are built.
The Advantage of Using a Mat Foundation
- This foundation can be built to be very shallow. It is very important when the soil is not in good shape.
- Through the mat foundation, the building's weight can be spread out over a large area.\
- It doesn't move during floods or other natural disasters because it can stand up to them well.
- This foundation can support more weight than other types of bases.
- A shallow base can be made with this foundation. So less needs to be dug for the building's foundation.
Mat Foundation's Disadvantage
- Because the mat foundation can cover a large area, it necessitates a large amount of steel and concrete.
- Mat foundation is more expensive than other foundations.
- Mat foundations are not appropriate for home construction. It does not necessitate a large foundation area.
- In the case of concentrated loads, the mat foundation requires special measurement.
- For the mat foundation, more shuttering materials are required.
- Expert labour is required for compaction of the mat base during concreting.
FAQ's
1. What is the minimum thickness of mat foundation?
- According to IS 1080, mat foundations must have a minimum depth of 50 cm. This is necessary to ensure that the soil has the safe bearing capacity assumed in the design.
- Shear requirements must be met by the depth of the mat foundation.
2. What is raft vs mat foundation?
The raft foundation differs from the mat foundation in that it is used when there is an uneven distribution of loading capacity and soil. When we want to achieve uniform distribution of loading capacity and soil, we use a mat foundation.3. What is the ratio of mat foundation concrete?
The amount of reinforcement required (for example, 0.0018 b h for Grade 60 reinforcing steel) is specified for each face (top or bottom). This is due to the mat reinforcement being designed to resist tensile stresses (rather than temperature or shrinkage) on the relevant (top or bottom) face of the mat, similar to the minimum reinforcement provided in RC beams.Other Posts
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