Short Answer:

Different types of foundations used in RCC (Reinforced Cement Concrete) structures include shallow foundations like isolated footing, combined footing, strap footing, and raft foundation, and deep foundations such as pile foundation and well (caisson) foundation. The type used depends on soil condition, load of the structure, and site constraints.

Shallow foundations are used where strong soil is available near the surface, while deep foundations are used for weak or deep soil layers. Each type ensures that the building remains stable, safe, and does not settle unevenly under load.

Detailed Explanation:

Different types of foundations used in RCC structures

In any reinforced concrete structure, the foundation is one of the most important parts, as it transfers the load of the building safely to the ground. The stability and safety of the entire building depend on the type of foundation used. The choice of foundation depends on several factors such as type of soil, load from the building, depth of hard strata, available space, and cost considerations.

In RCC structures, foundations are broadly divided into two categories:

1. Shallow Foundations
2. Deep Foundations

Let’s understand each type in simple language.

Shallow Foundations

Shallow foundations are provided when the soil bearing capacity is good and hard soil is available at shallow depth (usually less than 3 meters). These are economical and easy to construct.

1. Isolated Footing

• Used under single columns.
• Square, rectangular, or circular in shape.
• Common in small buildings where columns are spaced widely.

2. Combined Footing

• Used when two or more columns are close to each other.
• Their individual footings would overlap, so a combined one is made.
• Can be rectangular or trapezoidal.

3. Strap (or Cantilever) Footing

• Used when columns are not aligned symmetrically.
• Individual footings are connected by a strap beam to balance the load.
• Used where boundary conditions restrict symmetrical footing.

4. Raft or Mat Foundation

• A large concrete slab covering the entire building base.
• Used when column loads are heavy or soil is soft.
• Distributes the load over a larger area to reduce pressure on soil.

Deep Foundations

When good bearing soil is available only at greater depths, shallow foundations are not suitable. In such cases, deep foundations are used to transfer the load down to the stronger layers.

1. Pile Foundation

• Used when the topsoil is very weak.
• Long, slender columns (piles) are driven deep into the soil.
• Can be made of concrete, steel, or timber.
• Used in bridges, high-rise buildings, or loose soil areas.

2. Well (Caisson) Foundation

• Hollow wells made of concrete are sunk into the ground.
• Used mainly in bridges or water structures.
• Suitable for transferring load through waterlogged or riverbed soil.

Selection of Foundation Type

• Shallow foundations are preferred when the load is moderate, and soil is firm.
• Deep foundations are necessary when the load is high, or soil is weak at shallow depth.
• Soil investigation and load calculation help in making the right choice.

Conclusion:

RCC structures can have different types of foundations depending on site conditions and load requirements. Shallow foundations like isolated and raft footings are used when strong soil is available near the surface. Deep foundations like piles and wells are used when load must be transferred to deeper soil. Choosing the correct foundation type ensures the strength, safety, and stability of the whole structure.