In a previous article, the types of piles according to load transmission and functional behaviour were discussed. In this article named Classification of Piles: Material Type, the types of piles according to the type of material are discussed.
This page is about pile material. For the separate questions of how a pile transfers load and why a project may need piles, see classification of piles by load transmission and situations where piles are used.
Classification of piles by material
- Timber piles
- Concrete piles
- Steel piles
- Composite piles
Pile material comparison
| Material | Common forms | Useful where | Main strengths | Important limitations | Durability check |
|---|---|---|---|---|---|
| Timber | Round, tapered natural pile | Comparatively light loads, readily available timber, and suitable driving conditions | Low initial cost and easy handling | Difficult to splice and vulnerable to damage in hard driving | Treatment and exposure category; decay and marine-borer risk near changing water levels |
| Precast concrete | Reinforced or prestressed square, octagonal, circular, or hollow sections | Driven-pile work needing factory-controlled concrete and good durability | High resistance and hard-driving capability when properly designed | Heavy to handle; can crack during lifting or driving; field length adjustment and splicing need planning | Concrete exposure, cracking, reinforcement protection, and handling damage |
| Cast-in-place concrete | Bored or drilled pile, or concrete placed in a driven shell | Sites where length flexibility or lower vibration is important | Diameter and length can suit the ground profile; no transport of a full precast member | Bore stability, groundwater, cleanliness, reinforcement placement, and concreting quality require close control | Concrete mix, cover, casing, groundwater, and aggressive soil or water |
| Steel | H-pile or open-/closed-ended pipe pile | Long piles, hard driving, variable founding depth, or easy field splicing | High strength with relatively small section; easy to cut and extend | Major obstructions can damage or deflect a section; closed pipes may displace substantial soil | Site-specific corrosion assessment, especially in fill, marine exposure, or changing groundwater |
| Composite | Two materials joined along one pile, or a structural composite section such as concrete-filled steel pipe | Projects needing different properties at different depths or combined structural action | Can place strength or durability where it is most useful | The connection and load transfer between materials are critical design details | Each material, the transition, and the exposure at the connection |
Timber piles
Timber piles have been used since the earliest recorded times and are still used for permanent works where suitable timber is available. They are generally selected for comparatively light foundation loads, suitable ground and driving conditions, and local availability. The timber should be in good condition and should not have been attacked by insects.
Modern guidance treats pile size as a specification and species question, not as one universal length-and-tip rule. FHWA GEC 12 identifies ASTM D25 and AWPA exposure categories for timber piles. It also notes that timber is difficult to splice and vulnerable to damage in hard driving, so pile-head or pile-toe protection may be needed. The hammer, cushions, pile section, soil profile, and required resistance must be checked together.
Keeping the timber below the permanent groundwater level can protect it against fungal decay because oxygen is limited. However, this does not mean every wet timber pile is safe. Timber near a fluctuating water level can decay, and salt-water piles may also face marine-borer attack. Where treatment is required, specify the current AWPA Use Category and an accepted preservative system for the service exposure; do not assume that one historical treatment is suitable everywhere.
Concrete piles
Precast and prestressed concrete piles
Precast concrete piles are produced before installation and are commonly square, octagonal, circular, or hollow sections. Reinforcement is necessary within the pile to help withstand both handling and driving stresses. Prestressed concrete piles are also widely used because prestress helps control the tensile stresses that develop during lifting and driving.
A precast pile can provide factory-controlled materials and good durability, but its lifting points, storage supports, transport, hammer system, cushion, and driving stresses must be checked. A longer pile is not automatically assembled without consequence: any field splice or mechanical joint must be detailed and qualified for the forces it will carry.
Cast-in-place concrete piles
Cast-in-place piles include concrete placed in a drilled or bored hole and concrete placed in a driven shell. The former avoids driving a complete concrete member and can reduce vibration, but the bore must remain stable and clean until concreting is complete. Temporary or permanent casing, drilling fluid, or other support may be needed in unstable or water-bearing ground.
Historical examples in the original article
The original article used the Hercules pile joint, West’s shell pile, and Franki pile as examples. They are useful for understanding how prefabricated segments or driven shells have been joined and filled, but the names should be treated as historical or proprietary systems rather than current default choices. The dimensions and equipment below are retained as part of those examples, not as general design values.
The original article described the Hercules type of pile joint as easily and accurately cast into the pile and quickly joined on site. This remains a historical system example; a current project must use an approved connection detail and qualified installation.
Two of the main types used in the UK are: West’s shell pile : Pre cast, reinforced concrete tubes, about 1 m long, are threaded on to a steel mandrel and driven into the ground after a concrete shoe has been placed at the front of the shells. Once the shells have been driven to specified depth the mandrel is withdrawn and reinforced concrete inserted in the core. Diameters vary from 325 to 600 mm.
Franki Pile: A steel tube is erected vertically over the place where the pile is to be driven, and about a metre depth of gravel is placed at the end of the tube. A drop hammer, 1500 to 4000kg mass, compacts the aggregate into a solid plug which then penetrates the soil and takes the steel tube down with it. When the required depth has been achieved the tube is raised slightly and the aggregate broken out. Dry concrete is now added and hammered until a bulb is formed. Reinforcement is placed in position and more dry concrete is placed and rammed until the pile top comes up to ground level.
Current use, dimensions, equipment, testing, and acceptance must follow the selected system supplier and governing project specification.
Steel piles
Steel H-piles
Steel H-piles are suitable for handling and driving in long lengths. Their relatively small cross-sectional area combined with their high strength makes penetration easier in firm soil. They can be easily cut off or joined by welding. Any field weld or mechanical splice still needs an approved detail and qualified installation. FHWA guidance describes H-piles as well suited to toe bearing on rock, although drivability and obstruction risks still have to be checked.
Steel pipe piles
Pipe piles can be driven open ended or closed ended. An open-ended pipe may develop a soil plug; a closed-ended pipe behaves as a displacement pile. Pipe piles provide useful bending resistance and may be filled with concrete where the design requires it. The end condition, diameter, wall thickness, splice, and any internal concrete are therefore part of the pile definition.
Corrosion cannot be represented by one rate for every site. FHWA reports that steel embedded in natural, undisturbed soil often has limited corrosion because oxygen is scarce, while fill, the groundwater zone, marine exposure, low-pH soil, or other aggressive conditions may require special assessment. Possible measures include a corrosion allowance, suitable coating, concrete encasement, or cathodic protection. The project geotechnical and durability data determine what is justified.
Composite piles
A composite pile combines different materials in the same pile. As indicated earlier, part of a timber pile which is installed above ground water could be vulnerable to insect attack and decay. To avoid this, concrete or steel pile is used above the ground water level, whilst wood pile is installed under the ground water level. A modern structural example is a concrete-filled steel pipe. In either case, the joint is not a minor construction detail: it must transfer axial load, bending, shear, and any driving forces required by the design.
Do not confuse a composite pile with an ordinary reinforced-concrete pile. The term usually means that two pile materials or structural components are intentionally combined so that both contribute to the completed system.
How to select the pile material
No material is best for every project. Start with the ground investigation and the loads, then compare feasible pile systems.
- Ground profile: identify weak layers, dense layers, rock, obstructions, groundwater, fill, and aggressive soil or water.
- Required performance: check axial compression, uplift, lateral load, bending, settlement, scour, and design life.
- Installation effects: consider noise, vibration, soil displacement or heave, bore stability, access, headroom, and nearby structures.
- Drivability and constructability: check handling stresses, hammer compatibility, expected pile length, splicing, cutoff, and inspection.
- Durability: evaluate timber treatment, steel corrosion, concrete exposure, and the connection in a composite pile.
- Verification: set appropriate construction records, integrity checks, dynamic measurements, or load testing for the selected system.