Types of Pile Foundation: How They Work and How to Choose the Right One

How Pile Foundations Work

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Types of Pile Foundation by Material

1. 1. Concrete Piles

Concrete is the most widely used piling material globally. Concrete piles are available in two main forms: precast and cast-in-situ (bored).

Precast concrete piles are manufactured in a factory or casting yard, transported to site, and driven or jacked into the ground. They are available in square, circular, and octagonal cross-sections, and in pre-tensioned and post-tensioned configurations that improve their resistance to the tensile stresses that develop during driving. Precast piles are highly consistent in quality, because they are manufactured under controlled conditions, their strength and dimensions are reliable. They are commonly used in marine and waterfront construction, in bridge foundations, and in building foundations where driven piles are appropriate.

Cast-in-situ concrete piles (bored piles) are formed by drilling or boring a hole in the ground, inserting a reinforcement cage, and filling the hole with concrete. Bored piles can be constructed to large diameters (up to 2 metres or more) and deep lengths, making them capable of carrying very high loads. They produce no driving vibration, a significant advantage in urban environments adjacent to existing structures. The quality of cast-in-situ piles depends heavily on the workmanship during installation, proper cleaning of the borehole, correct reinforcement placement, and continuous tremie concreting are all critical to producing a sound pile.

Best suited for: Multi-storey building foundations, bridge piers, marine structures, any project where high load capacity and long service life are required.

1. 2. Steel Piles

Steel piles are available in several profiles, H-piles (wide-flange sections), pipe piles (hollow circular sections), and sheet piles (interlocking sections used for earth retention rather than vertical load transfer). For vertical load-bearing applications, H-piles and pipe piles are most common.

Steel H-piles are driven through hard or dense soils that would damage or break a concrete pile during installation. Their relatively small cross-sectional area allows them to penetrate dense sands, gravels, and soft rock layers that resist concrete pile installation. They are commonly used in rock-bearing applications where the pile tip must be driven to refusal on bedrock.

Steel pipe piles can be driven open-ended (allowing soil to enter the pipe) or closed-ended (with a flat plate welded to the tip). Open-ended pipe piles can penetrate dense soils more readily; after driving, the interior may be cleaned out and filled with concrete to increase load capacity and corrosion resistance.

Best suited for: Rock-bearing applications, dense granular soils, projects requiring high penetration resistance, marine and offshore structures.

Limitations: Steel piles are vulnerable to corrosion, particularly in marine and aggressive soil environments. Adequate corrosion protection, through coating, cathodic protection, or increased wall thickness, must be specified for the expected design life.

1. 3. Timber Piles

Timber piles are the oldest form of pile foundation, used in construction for thousands of years. Driven timber piles made from straight-grained hardwood or softwood species remain in use in certain applications, particularly in marine structures, jetties, and temporary works, where their low cost, easy availability, and adequate structural performance make them a practical choice.

Modern timber piles are typically treated with preservative compounds to resist biological degradation. Their load capacity is lower than concrete or steel piles of comparable dimensions, which limits their application to relatively light structures.

Best suited for: Marine and waterfront structures, jetties, light residential buildings on soft ground, temporary works and falsework.

Limitations: Lower load capacity than concrete or steel. Susceptible to biological degradation above the water table where alternate wetting and drying occurs. Not suitable for heavy structures.

Types of Pile Foundation by Installation Method

1. 1. Driven Piles

Driven piles are installed by applying repeated impact force to the top of the pile, using a drop hammer, diesel hammer, hydraulic hammer, or vibratory hammer, driving it progressively into the ground. The driving resistance increases as the pile penetrates to denser or stiffer soil layers, and driving continues until the pile reaches its design set (a specified penetration per blow that indicates sufficient bearing capacity has been achieved).

Driven piling is fast and productive on suitable sites. The installation process also densifies the surrounding soil (particularly in granular soils) through displacement, which can increase the load capacity of adjacent piles and improve the overall ground conditions.

Key advantages:

• • • Fast installation rates
    • Suitable for a wide range of pile sizes and materials
    • Installation provides direct evidence of ground resistance through blow count monitoring
    • Displacement effect improves surrounding soil

Key limitations:

• • • Generates significant noise and vibration, problematic in urban environments adjacent to existing structures or vibration-sensitive equipment
    • Hard driving can damage pile heads and tips
    • Not suitable for all soil conditions, cobbles, boulders, and very dense layers can deflect or damage driven piles

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1. 2. Bored Piles (Drilled Shafts)

Bored piles are installed by drilling or boring a circular hole in the ground using rotary drilling equipment, then placing the reinforcement cage and filling with concrete. The borehole may be supported during drilling by a temporary steel casing, by a permanent casing, or by a drilling fluid (bentonite slurry or polymer fluid) that provides hydraulic pressure to prevent the borehole walls from collapsing.

Bored piling produces no driven vibration, making it the preferred method in urban areas, near existing structures, and on any site where vibration-sensitive conditions exist. Large-diameter bored piles, often called “barrettes” in certain configurations, can carry extremely high loads, making them the standard choice for high-rise building foundations in many parts of the world.

The drilling rigs used for bored piling range from compact track-mounted units for small-diameter piles to large crane-hung Kelly drilling rigs for large-diameter deep piles. The logistics of operating heavy drilling equipment, positioning, ground preparation, and access, requires the same careful planning that applies to all heavy machinery operations on construction sites.

Key advantages:

• • • No vibration during installation
    • Can achieve very large diameters and depths
    • Suitable for use near existing structures
    • Minimal noise compared to driven piling

Key limitations:

• • • Slower than driven piling for equivalent numbers of piles
    • Quality highly dependent on workmanship
    • Disposal of arisings (excavated spoil) must be managed
    • Ground conditions may require support fluid management

1. 3. Screw Piles (Helical Piles)

Screw piles, also called helical piles or helical anchors, consist of a steel shaft with one or more helical plates (flights) welded along its length. The pile is installed by rotating it into the ground using a hydraulic motor mounted on an excavator, eliminating the need for either driving or boring.

The rotating action of the helical flights pulls the pile into the ground with minimal soil disturbance. Screw piles can be installed quickly, require no arisings removal, produce no vibration, and can be loaded immediately after installation without any concrete curing time. They are also removable, an advantage for temporary works applications.

Best suited for: Temporary structures, light to medium permanent buildings, sites with restricted access where larger piling rigs cannot operate, environmental restoration projects, areas where soil disturbance must be minimised.

Limitations: Load capacity is limited by the helix diameter, shaft size, and soil conditions. Not suitable for very high loads or for penetrating hard rock or dense obstructions.

1. 4. Micropiles (Mini Piles)

Micropiles, also called mini piles or pin piles, are small-diameter (typically 75–300 mm) drilled piles that are used where access is restricted, loads are moderate, or existing structures must be underpinned. They are drilled and grouted rather than driven, producing no vibration. Their small diameter allows them to be installed inside existing buildings, in low-headroom situations, and in any location inaccessible to full-size piling rigs.

Micropiles are commonly used in underpinning existing foundations, strengthening ground beneath existing structures, and providing foundation support in heritage buildings where disruption to existing fabric must be minimised.

Best suited for: Underpinning, restricted access sites, low-headroom environments, heritage structures, seismic retrofit foundation strengthening.

1. 5. Contiguous and Secant Bored Pile Walls

While individual bored piles are used for vertical load bearing, arrays of bored piles are also used to form earth retention walls for basement excavations, cut slopes, and below-ground structures.

Contiguous bored pile walls consist of bored piles installed in a row with a small gap between adjacent piles. They provide earth retention but are not fully watertight, groundwater can pass between the piles. They are used in relatively dry ground conditions where water ingress is manageable.

Secant bored pile walls consist of alternating “primary” and “secondary” piles where the secondary piles are bored to overlap with the adjacent primary piles, cutting into them and forming a continuous interlocked wall. Secant pile walls are watertight and are used in basement construction where groundwater exclusion is essential.

Key Factors in Pile Type Selection

• • Ground conditions

The soil profile, its stratigraphy, strength, compressibility, and water table, is the primary determinant of pile type suitability. A geotechnical investigation (borehole drilling and in-situ testing) is essential before any piling specification can be made.

• • Structural loads

The magnitude and nature of the loads to be transferred, axial compression, tension (uplift), and lateral loads, determine the required pile capacity and, consequently, the pile diameter, length, and number.

• • Site constraints

Urban sites near existing structures require low-vibration, low-noise installation methods. Sites with restricted access or low headroom require compact piling equipment. Contaminated sites require careful management of arisings.

• • Programme

Driven piling is generally faster than bored piling for equivalent pile numbers. Where programme is critical, the installation rate of different pile types, typically expressed as piles per shift, must be factored into the comparison.

• • Cost

Pile cost depends on material, installation method, pile size, and quantity. Driven precast piles are generally cost-effective at moderate load levels. Large-diameter bored piles carry higher unit cost but can replace many smaller piles.

• • Environmental impact

Noise, vibration, spoil disposal, and groundwater management are all environmental considerations that affect pile type selection, particularly in urban, sensitive, or regulated environments.

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