Mat Foundation Structural Guide and its Uses: A Takeaway for You
A mat foundation, or raft foundation, is a concrete slab placed on the ground as a building's foundation. There are many occasions when a mat foundation is constructed, including the construction of buildings, bridges, and towers. The raft foundation is the last option when dealing with shallow foundations.
The footing area needs to increase due to the increased axial loads on the structure or due to poor ground conditions. With increasing footing dimensions, the overlapping of the stress bulbs creates weak zones. As a result, we chose the raft foundation.
Raft or mat foundations provide support for the superstructure by carrying the entire load and dispersing it over a large area beneath the building. In addition to providing differential settlement control, it is one of several shallow foundations.
Construction of Mat Foundation
1. To achieve a uniform and flat surface, dig out the dirt and excavate the soil. A ramming process uses to compact the soil. Once that has been completed, a waterproof plastic sheet layer over the top.
2. After pouring a layer of cement concrete around 7 cm thick to create a perfectly level and flat foundation. Reinforce the foundation bed with spacers. You can use steel mesh reinforcements on both sides of the foundation. The foundation is reinforced with two meshes at the top and bottom to balance upwards and downwards bending forces.
3. A small building's concrete is usually poured up to a specified thickness after the steel has been erected from 200mm to 300mm. That can get much thicker if heavy loads are to carry. Rebar covers should maintain at a minimum of 50mm. A suitable curing regime should ensure concrete reaches the desired compression strength.
Types of Mat Foundation
Slab & Beam Raft Foundation
The flat plate or projections from the flat plate cannot bear any further increase of axial column load. The foundation reinforces with beams. The beams reduce the thickness of the raft slab significantly.
Cellular Raft Foundation
The cellular raft foundation is the next step after the beam raft foundation. You also install the top slab in this type of foundation. As a result, the mat foundation is further stiffened.
Flat Plate Foundation (Above & Under)
Flat plates reduce the load applied on a mat foundation. Both the projection above and the projection below the flat plate are the same. It is much easier to build a projection above the raft's surface. Nevertheless, you can only do this if the raft slab is non-usable or if the remaining spacing is adequate for the purpose.
The increase of axial column loads increases bend and shear reinforcements. Construction costs rise as a result. Further, beyond a certain point, the mat foundation has to be thicker.
It is not economical to add thickness to the whole mat foundation. As a result, we thicken the mat foundation beneath the columns. However, construction might prove problematic because the projection is below the flat plate. A lot of work will require installing the reinforcement, waterproofing, etc.
Pile Raft Foundation
A pile raft foundation uses when piles cannot socket into the rock and when the end bearing of a pile is not adequate. It is a complex process to design and construct a pile raft foundation. After the pile takes the first load, the raft foundation starts sharing the load. The raft begins carrying the full load after the piles fully mobilize. Eventually, the raft carries all the weight.
Uses of Mat Foundation
Construction of commercial buildings often involves the use of rafts or mat foundations. Basements commonly use mat foundations.
Additionally, mat foundations use to support low-bearing capacity soils, thereby allowing the building load to spread evenly and thereby constructing a stable foundation. Mat foundations reduce differential settlement of buildings.
If the soil layer is unstable, raft or mat foundations are used. Strip foundations typically cover more than 70% of the ground beneath a building. Movements of the soil layer can also occur in mining areas.
To learn more, watch the following video tutorial.
Video Source: CE&T - NH? XANH VI?T NAM
Wrapping it Up
When compared to a conventional strip or trench footing, the mat foundation spreads beneath the footprint of a building and reduces contact pressure.
Embedded in the ground, the superstructure of a mat foundation cannot simply consist of a flat plate. A higher axial load will also result in a greater cost for construction work. The pile foundation could even exceed a certain level of construction. A raft foundation could further support buildings up to ten floors.