Steel pipes are commonly used in precast piles and driven cast-in piles for foundation work. Precast piles can be classified into hollow small displacement piles and solid piles, with steel pipes being used for the former and steel H-piles for the latter. Driven cast-in place piles can be classified into concrete tube and steel tube piles, with the latter being further divided into closed-ended and open-ended tubes.
Steel piles are also classified as screw piles, disc piles, H-piles, and rolled steel H section or pipe piles. The thickness of the web and flange is the same for H-section piles, while I-section or wide flange piles have a thinner web compared to the flange. The allowable structural capacity, Q, can be determined by multiplying the cross-sectional area of the steel, A, with the allowable stress of the steel, fs, as expressed by the equation Qall = A x fs. During geotechnical investigation, the design strength, Qdesign, must be within the allowable structural capacity, Qall.
Connections in Steel Piles
The H-pile in Figure-1 is being spliced using either welding or riveting, depending on the requirement. This splicing process involves joining steel piles together using welding or rivets.
Fig.1: Splicing of H-Pile by means of (a)Welding (b) Rivets and Bolts
Figure-3 illustrates two possible types of bottoms for the pile ends: a flat bottom or a conical bottom. Both options are connected using welded connections, as depicted in the diagram.
Fig.2: Steel Piles with flat bottom and conical bottom
In order to make it easier to drive piles into hard soils such as soft rock, shales, and dense gravel, driving shoes or driving points are used. Figure-2 shows two types of shoe options that can be used for the piles to facilitate their movement in these challenging ground conditions. These shoe types are designed specifically to provide better performance and efficiency when driving piles into hard soils, making the process smoother and more effective.
Types of Steel Pile Foundations
1. Pipe Piles
Pipe piles are a type of foundation element that is commonly used in construction to provide support to structures. They are typically made of seamless steel pipes that are welded together to create a strong and durable pile. Pipe piles can be used to provide either friction or end bearing support, depending on the requirements of the project.
There are two main types of pipe piles: open end piles and closed end piles. Open end piles are designed with an open bottom that allows the pile to penetrate through soft soil layers and reach harder, more stable soil layers below. This type of pile is often used in areas with loose or weak soil conditions.
Closed end piles, on the other hand, are designed with a closed bottom that is either sealed or filled with concrete. This type of pile is typically used in areas where the soil conditions are more stable and able to support the weight of the structure without the need for deep penetration.
The driving of these piles can be carried out using a variety of methods, including hydraulic hammers, vibratory hammers, and impact hammers. The choice of driving method will depend on the soil conditions, the size and weight of the pile, and other factors specific to the project. Regardless of the method used, the driving process must be carefully controlled to ensure that the pile is properly seated and able to provide the necessary support to the structure.
Open End Pipe Piles
Pipe piles that are designed for penetrating hard or rocky strata are commonly utilized in construction projects. These piles are first driven into the soil and then further sunk to the desired depth. The removal of soil within the steel pipe is typically accomplished through compressed air or a water jetting process. Once the pipe has been driven to the required depth, it is filled with concrete that meets standard specifications. This process results in a sturdy and reliable foundation that can support the weight and load of a structure.
Close End Pipe Piles
Pipe piles with conical shoes have a unique design where a conical element made of steel or cast iron is welded to the open bottom. This design allows for the pipe to be driven into the soil and filled with concrete. The diameter of these pipe piles can range from 0.25m to 1.2m, and their thickness can vary between 8 to 12mm. This type of pile foundation is particularly effective for larger structures, where the pile foundation needs to be greater than 30 inches in size. By using conical shoes in the design of these pipe piles, the load capacity of the pile foundation can be greatly increased, providing a stable and reliable foundation for large-scale construction projects.
2. Screw Piles
Screw piles are typically constructed using steel or cast iron, and consist of a long shaft that terminates at the end in the shape of a screw base or helix. The shaft can be either hollow or solid, depending on the specific design of the screw pile.
Fig.3: Screw Piles
Screw piles are used for foundations in various soil types, especially in clay or loose soils, where they are driven into the ground by an electric motor for easy penetration. The base of the screw has a diameter that ranges from 0.45 to 1.5 meters. This method of steel screw piling increases the bearing area and makes installation of pile foundations in these types of soils more manageable. The screw bottom is designed to aid in the penetration of the strata, making it an effective solution for building on unstable or challenging ground.
3. Disc Steel Piles
Disc steel pipes are designed with a structure similar to screw piles, with a cast iron disc affixed to the bottom. As these piles penetrate the soil, they are capable of sinking into it. In order to aid the water jetting process, a hole is created at the bottom of the pile. This type of pile is typically utilized in soft or sandy soil, where the sinking of disc piles can be facilitated during the water jetting process. Disc piles are commonly used for marine construction projects, where significant total penetration is required.
4. H-Piles
In the piling industry, there is a new technology that involves using rolled steel H-beams as bearing piles. This type of pile is capable of withstanding significant impact forces and stresses that occur during hard driving into the soil strata. H-piles are particularly useful for penetrating areas with rock or other hard strata, and do not require additional methods such as jetting, coring, or adoption. The small cross section of H-piles also facilitates the soil displacement process. Overall, the use of H-piles as bearing piles represents a promising development in the field of piling.
Advantages of H-Piles
H-piles are a popular choice for construction projects due to their various advantages. One of their key benefits is that they require less space for storage, making them a convenient option for sites with limited space. Additionally, the handling of H-piles is relatively easy, allowing for efficient and smooth construction processes.
H-piles also have the advantage of being able to penetrate closer to existing structures. Furthermore, the amount of displacement caused in the surrounding area during the penetration process is minimal, making them a safe and practical choice for many construction projects.
Another advantage of H-piles is that splicing them together is a simple process. Moreover, they can be driven to depths of up to 100m, providing a strong and stable foundation for a wide range of construction projects. H-piles also serve the dual function of both friction and compaction piles, making them a versatile choice for many different applications.
In practice, H-piles are commonly used in a variety of construction projects, including trestles, retaining walls, cofferdams, and bridges. Their unique set of advantages make them an attractive option for many different types of projects, and their popularity is likely to continue for years to come.
Corrosion of Steel Piles
Steel pipes, regardless of their type, are prone to corrosion. To mitigate this issue, protective measures can be taken. One option is to coat the pipes with coal tar or a corrosion-protecting coating. Another approach involves encasing certain chemicals or materials in concrete to prevent corrosion. These methods can be effective in prolonging the lifespan of steel pipes and reducing the need for frequent maintenance or replacements.