What Is A Raft Foundation In Construction?
What Is A Raft Foundation In Construction?
Raft foundations are a reliable and cost-effective form of foundation used in construction. It is made up of four foundation piers connected together using a thick concrete slab.
The foundation piers are connected through reinforced steel beams, which enable them to occupy the whole area beneath the structure, thereby leading to increased load-bearing capacity and strong resistance against settlement.
The raft foundation is thus able to transfer all the load from the building to the ground evenly, making it an ideal choice for heavy structures such as offices, hotels, or multi-story apartments on relatively soft soil conditions.
What Is The Main Reason For Using A Raft Foundation?
The main reason for using a raft foundation is to ensure that the structure’s structural integrity is maintained while also allowing for expansive ground movements, making it an ideal choice for areas that are prone to earthquakes or other seismic activity.
A raft foundation is mainly used to spread the load of a building across a wide surface area beneath it, reducing the stress on the ground and providing a stable foundation even when there is ground movement.
What Is Raft Vs Pile Foundation?
Raft and pile foundations are two of the most common types of foundations used in construction.
A raft foundation, or mat foundation, is a shallow foundation that is built by pouring a thick concrete slab that covers an entire area while piles are deep foundations typically constructed by driving steel or reinforced concrete columns into the soil to provide additional support below the ground surface.
The main difference between these two types of foundations is their depth; raft foundations only extend up to several inches and have a limited load-bearing capacity, while piles extend much deeper and can bear more weight.
Additionally, while the cost of installing a pile foundation is usually higher than that of a raft foundation due to its complexity, it can be highly beneficial for soils with weaker bearing capacities or special loads requiring deeper penetration.
What Is The Maximum Depth Of The Raft Foundation?
The maximum depth of a raft foundation depends mainly on the soil composition. Generally, raft foundations on clay should have a maximum settlement of 65 to 100 mm while those placed in sandy soils should be kept to 40 to 65 mm.
This is because soils with higher cohesion and friction capacity can better bear a load of a larger foundation while sand has a lower bearing capacity and therefore requires slightly shallower depths.
What Is The Minimum Depth Of The Raft Foundation?
The minimum depth of raft foundation is 50cm which must be excavated to a depth of 2.5m and reinforced with a rebar cover of 50mm to ensure the design is adequate.
The selection of material, thickness, and type of the raft slab depends upon the intensity and nature of loads carried by the foundation whilst also taking into account groundwater level and soil bearing capacity.
Additionally, where greater stiffness or higher load-bearing capacity is needed, reinforced concrete pad foundations may be used instead.
