The construction and civil engineering landscape is ever-evolving. In this, the choice of foundation system plays a critical role. It also stands as a decisive factor for the project’s success. Deep foundations are vital in building structures. They give stability and strength in unpredictable soil conditions and urban environments.
The demand for deep foundations is expected to increase significantly in the coming years, with the piling method having a significant impact on the construction industry.
Two predominant types of deep pile foundations are:
- End bearing piles
- Friction piles
Read on to learn more about the differences between these two types.
What is an End Bearing Pile?
End-bearing piles are used to transfer the structural load into stronger layers of the soil. It is also known as point-bearing piles. This is a type of deep foundation in which the load is transferred from the weak layer to the stronger soil.
This load is transferred to the bottom tip, and the pile acts like a column which provides support to the above structure. The end-bearing pile is ideal for surfaces with weak soil. Also, they are used for heavy concentrated loads. This includes bridges, high-rise buildings, and water tanks.
What is a Friction Pile?
Friction piles transfer the load to the soil. However, it is done primarily through skin friction along their length. These are also called floating piles. Often, friction piles are made from various materials like concrete, steel, and timber. It is commonly used in areas with deep, soft soil. In this case, end-bearing piles are not feasible.
The design involves calculating the pile’s bearing capacity, which is based on soil properties and pile dimensions. Typically, the load is transferred through the pile’s surface area in contact with the soil. It can be driven to greater depths, often up to 20 meters or more.
Differences Between End Bearing Pile and Friction Pile
Load Transfer Mechanism
Piles are structural elements which transfer the load of a building or structure from a weaker to a more stable layer of soil.
End bearing:
The load carried by the pile is transferred entirely. It passes through the pile’s top or bottom. The pile penetrates through weaker, compressible soil layers. It then reaches a firm, stable layer, which may be rock or dense sand. This layer has a high load-bearing capacity. The pile acts like a column and transfers the load below.
Friction Pile:
Friction piles rely on the interaction between the pile’s surface and the surrounding soil. This helps to support the load. The pile’s surface area contributes to load transfer. There is frictional force that occurs between the pile shaft and the surrounding soil.
The load is gradually distributed along the length of the pile. It is not concentrated at the tip. Therefore, the soil layers themselves can produce enough friction to carry the load.
Suitable Soil Conditions:
The soil type is specified based on the pile type. It is primarily determined by the strength and soil conditions.
End Bearing Pile Ideal Soil Conditions:
- End-bearing piles are ideal when hard soil layers are available below. These are generally solid, non-compressible layers. For example, bedrock, dense gravel, or compacted sand. It should be available at a reasonable depth from the surface.
- The upper surface layer is soft and compressible; load must be transferred to the bottom.
- An end-bearing pile is designed to penetrate through these weaker layers. It reaches the solid layer to gain adequate support.
Friction Piles Ideal Soil Conditions:
- Friction piles get support from soils that can generate significant friction. It includes clay, silt, and sand.
- The subsoil is predominantly soft and cohesive. There is no firm layer present. In such circumstances, friction piles are ideal. It can transfer the load deeper into the soil.
- Soft to medium-stiff clays, loose to medium-dense sands, silts, and similar soils can offer surface friction. These do not possess high bearing capacity at any specific depth.
Load Distribution:
- End Bearing Pile:
The load is concentrated at the pile tip. The majority of the load is concentrated at the bottom tip of the pile. The strong layer is deep in the soil profile. It can bear the load.
- Friction Pile:
The load is distributed along the entire length of the pile. It is transferred from the pile shaft to the surroundings. As the pile is driven deeper into the soil, more surface area is engaged, and friction increases.
Shape
End Bearing Pile:
It can be circular or H-shaped. They are based on the structural and soil conditions. Circular piles are commonly used in drilled piles. The main focus is transferring load to a firm layer. H-shaped steel piles are often used because of their cross-section. It provides strength and penetration power. Also, significant resistance that is required during installation is provided.
Friction Pile:
It is generally circular to maximise surface contact. A circular cross-section provides a uniform distribution of stress and increases the frictional interaction with the surrounding soil. It is more effective in distributing load through friction along the entire pile length.
Settlement
End Bearing Pile:
It shows minimal settlement if the firm layer is reached. The load from the structure is transferred directly to the firm layer. It passes through the pile tip. This prevents the pile from sinking further. This makes end-bearing piles ideal for projects requiring high stability and minimal settlement.
Friction Pile:
It may experience more settlement due to soil compression. It can compress under the weight of the structure. However, the settlement occurs as the soil around the pile shaft compresses or consolidates. It occurs especially in softer or more compressible soils like clay or loose sand. The softer the soil, the greater the potential for settlement. This is why friction piles may require longer monitoring.
Conclusion
In conclusion, both end bearing and friction piles are important in modern construction. Their distinct functionalities make them suited for different scenarios. End-bearing piles transfer loads directly to stronger, more stable layers. This makes them ideal for structures in densely built environments with high load requirements. Friction piles, on the other hand, distribute loads along the length of the pile and are suitable when there is no strong soil available at any depth.
Understanding the differences between these two pile systems is critical in optimising construction designs. It ensures sustainability and minimises risks in today’s rapidly evolving urban landscape. By carefully selecting the right pile type, engineers can enhance the safety and efficiency of projects..