Various types of materials can be used for piles. The magnitude of the applied loads from the superstructure, the subsurface conditions, and the location of the groundwater table are just some of the factors in selecting the correct material for pile foundations.
At present, steel and concrete are commonly used for pile foundation construction. Steel piles are generally installed by driving the pile into the ground by either an impact hammer (dynamic installation) or by pressing the steel pile into the subsurface layers until it reaches the desired depth (non-dynamic installation).
Steel piles are often shaped as pipes, I-sections, W-sections, and H-sections. Engineers prefer the H-sections compared to I and W sections since H-shaped sections tend to have equal web and flange thicknesses.
Steel pipe piles have a wide range of applications. These are used as building foundations, and bridge piers/foundations. Pipe piles are also utilized for port projects as foundation for piers and wharves. The piles can also be interlocked to form a continuous wall to retain soil from the backside such as quay walls, cofferdams, and excavation protection structures.
Pipe piles have an advantage over the other pile materials and shapes, and can be enumerated as follows:
1. High pile axial capacity – pipe piles usually are large in diameter. Recall that a pile’s axial capacity can be attributed to its skin (or frictional) resistance, and its end-bearing (or pile tip) resistance. Both components are dependent on the geometry of the pipe pile, such that the skin resistance increases with the pile’s surface area, and the tip resistance is a function of the pile’s cross-sectional area.
2. High flexural strength – steel generally has a high yield strength, and this translates to high bending moment capacities that can resist flexural stresses due to the loads from the superstructure (for building and bridge structures), or the lateral earth pressures from the retained soil (for earth-retaining structures).
3. Pipes can be used as main components for a combination wall – for sheet pile applications, pipe piles can be used as the main flexural member (usually referred as a King Pile) of the continuous wall, in combination with infill sheet piles (usually a pair of U or Z sheet piles placed between two pipes). This configuration for a continuous wall provides a higher bending moment capacity while maintaining an optimized wall design (i.e., a lower total tonnage of steel is required).
4. Pipe piles can be part of a composite pile – in most cases in engineering projects, steel pipe piles are filled with concrete after the pipes have been driven into the ground, turning it into a composite pile. Having a concrete-filled pipe pile increases the rigidity of the pile element, and provides better performance in resisting various external loads, for both static and dynamic (i.e., earthquake loads or wind loads) conditions.
5. Ease of installation and jointing – due to the geometry of a pipe pile, jointing of piles by welding is relatively easier as compared to other steel structural shapes. This in turn provides a more efficient construction method and can potentially lessen the overall construction duration of the project.
The use of steel pipe piles as foundation and/or earth-retaining structures has been found effective in providing resistance against numerous combinations of gravity and lateral forces. In most cases it has been found as a more cost-effective foundation solution compared to conventional concrete piles (for foundation purposes), and typical U and Z sheet piles (for retaining walls).
Through the combined efforts of design engineers/ engineering consultants and pile manufacturers/suppliers, value engineering and sustainable development can both be satisfied for a wide array of projects.
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