Pile Foundation and It's Types | Bridge Engineering | Lec - 05

Summary

This video discusses the different types of foundations used in construction, focusing on shallow and deep foundations. It explains when pile foundations are necessary, particularly in areas with weak soil, high water tables, or erosion risks. Pile foundations are categorized into end bearing and friction piles, with their load-bearing capacities explained. The video also covers different materials used for pile construction, such as timber, steel, and concrete, and the methods of installation, including driving and boring. The importance of selecting the right foundation type for structural stability is emphasized.

Takeaways

• 😀 Foundations are the lowest part of a structure, transferring loads from the structure to the soil safely.
• 😀 Shallow foundations are used when the depth is less than or equal to the width of the foundation (Df/Bf ≤ 1), and are ideal for lighter structures.
• 😀 Deep foundations are used when the depth of the foundation exceeds its width (Df/Bf > 1) to support heavier structures or weak surface soil.
• 😀 Pile foundations are a type of deep foundation that transfers loads to deeper, stronger soil layers when surface soil cannot support the structure.
• 😀 Shallow foundations are economical for light to moderate loads, but pile foundations are required for large, heavy structures.
• 😀 Pile foundations are particularly useful in areas prone to soil liquefaction, high water tables, or where settlement might cause damage.
• 😀 Pile foundations help resist horizontal and uplift forces that may be caused by rising water tables or other environmental factors.
• 😀 Types of pile materials include timber, steel, concrete, and composite piles, which can be driven into the ground or placed via drilling.
• 😀 End bearing piles transfer load directly to hard soil or rock layers at the bottom of the pile, acting like columns.
• 😀 Friction piles transfer loads through friction between the surface of the pile and surrounding soil, typically used when hard strata are deep.
• 😀 Piles can also be installed close together to compact the soil, increasing its bearing capacity and providing lateral support.

Q & A

What is the main function of a foundation in construction?

The main function of a foundation is to transfer the loads of a structure to the underlying soil, ensuring the stability and safety of the structure.

How are foundations classified based on their depth and width?

Foundations are classified into shallow and deep foundations. A shallow foundation has a depth equal to or less than its width (Df/Bf ≤ 1), while a deep foundation has a depth greater than its width (Df/Bf > 1).

Why are pile foundations used instead of shallow foundations?

Pile foundations are used when the underlying soil is weak and cannot bear heavy loads, especially in areas where large, heavy structures are built, or where settlement and soil liquefaction are concerns.

What are the advantages of pile foundations in areas with high water tables?

Pile foundations can penetrate through water to reach stable soil layers, making them an ideal solution when the water table is high and shallow foundations would be ineffective.

How do pile foundations help prevent settlement in weak soils?

Pile foundations transfer the loads from the structure through weak soil to stronger, deeper layers of subsoil, which prevents settlement and damage to the structure.

What are the different types of piles used in pile foundations?

The different types of piles include timber piles, steel piles, concrete piles, and composite piles, each selected based on the specific needs of the construction project.

What are the two methods of installing piles?

Piles can be installed by two methods: driven piles, which are hammered or vibrated into the ground, and bored piles, which involve drilling holes to the required depth, inserting reinforcements, and filling them with concrete.

How do end-bearing piles work and how is their capacity calculated?

End-bearing piles transfer loads through weak soil to a hard layer of soil or rock at the pile's bottom. Their capacity is calculated by multiplying the pile's cross-sectional area at the end by the bearing capacity of the hard soil.

What is the function of friction piles and how is their capacity determined?

Friction piles transfer loads through friction between the pile surface and the surrounding soil. Their capacity is determined by multiplying the pile’s surface area by the safe frictional force per unit area.

Why are piles sometimes placed in close intervals and what benefits does this provide?

Piles are sometimes placed in close intervals to compact the surrounding soil, increasing its bearing capacity. This also helps provide lateral support and resist lateral pressures, such as those from loose soil or water flow.