Pile Raft

The piled raft is a foundation that is built by combining a raft foundation with piles. After building the piles, the raft is next set on top of all the piles. The primary component taken into account while building the Piled Raft Foundation is the interaction of the pile, earth, and raft. The inexpensive design is the result of the interaction being used effectively.

Pile raft foundation

A pile raft foundation is a hybrid design that combines two foundation-building methods and is appropriate for unique situations. The building’s weight is dispersed over the ground by the raft or spread foundation.

Imagine it as a raft supporting a structure that is floating on the ground. Underground columns that join at the top of the building are called piles. Both techniques are employed in a stacked raft foundation to support the structure.

Principle of Raft Foundation Operation

It’s critical to comprehend how to raft foundation functions in order to have a better understanding of when to employ it. Let’s quickly go through its guiding idea. The whole ground floor area receives the full weight of the structure through the raft foundation.

The raft foundation’s stress distribution system is fairly straightforward. Calculating the stress on the soil involves dividing the combined weight of the structure and the mat by the entire area of the foundation it is covering.

Because raft foundations have a greater amount of soil contact than other types of foundations, the load is dispersed over a broader area, reducing stress on the soil and lowering the risk of shear collapse of the soil.

Design philosophies

Traditional method

The majority of the weights may be carried by the piles as a group, with certain loads being supported by the raft foundation.

Crawling piles

A sufficient number of piles are included to lower the net contact pressure between the raft and the soil to below the soil’s pre-consolidation pressure. Piles are designed to operate at a working load at which significant creep starts to occur, which is typically 70% to 80% of the ultimate load capacity.

Various settlement control

Instead of significantly lowering the average settling, piles are placed deliberately to lessen the differential settlement.

Piled Raft Foundation
Piled Raft Foundation

When to use a raft foundation

When there is no solid layer of soil at or near the ground surface, architects employ raft foundations. This indicates that the bedrock is too deep to be reached by a typical foundation and that the surface soils are not solid enough. The weight is dispersed over the ground by the raft foundation.

How to use raft foundation

To provide a sturdy platform, piles are pushed into the earth. Usually, bedrock, however, other stable materials may also be used. Based on the weight and size of the building, engineers choose the number and size of the piles. The structure is protected from any movement of the soil at the top levels by the piles that secure it to the bedrock.

Foundation with deep strips

The Deep Strip Foundations are the most typical and least expensive form of foundation, providing the soil conditions are acceptable. The walls are supported by a strip of reinforced concrete. Any depth for the trench is acceptable, but it must be at least 40 inches deep and 24 inches wide. Concrete should be poured at least nine inches deep.

Type of shallow foundation

There are many different kinds of shallow foundations, including strip foundations. When the ground’s ability to carry loads has been assessed and found to be adequate for the project, they may be employed to support load-bearing walls.

Closely clustered columns can also be supported by strip foundations. In order to determine the overall load-bearing capacity of the plot, any weaker areas, and any additional factors, such as access restrictions, water flows, or other conditions that might impact the foundations, it is crucial to carefully evaluate the ground conditions across the entire footprint of the building.

Soil suitability

Strip foundations have the advantage of being appropriate for the majority of subsoils and the lesser structural loads present in residential buildings. When the ground is stable and mass concrete can be used, strip foundations are typically employed.

A strip foundation would need to be 900mm wide to accommodate a normal exterior cavity wall of 300mm (100mm block, 100mm cavity, 100mm block). Depending on the structure, the concrete will typically be at least 300mm deep.

Some construction projects can call for using steel reinforcement within the concrete itself or adding extra concrete.