Bored & CFA Pile Reinforcement Cages

Bored & CFA Pile Reinforcement Cages — Technical Overview

Bored pile cages and CFA (continuous flight auger) pile cages are among the most technically demanding reinforcement assemblies in ground engineering. The cage must survive the installation process — lifted vertically, lowered into a fluid-filled bore or extruded through augered spoil — while providing the structural capacity required by Eurocode 2 (EN 1992-1-1) design. Steel Rebar Germany supplies all cage components to DIN 488 and EN 10080: hot-rolled B500B deformed bars for the main longitudinal reinforcement, cold-rolled B500A coil stock for spiral helical links, and precision cut-and-bent stirrup rings.

Typical cage geometry consists of longitudinal bars (usually 6, 8, 10 or 12 bars) arranged around a circular pitch circle diameter, held at regular intervals by helical (spiral) links or discrete circular links. The helix pitch is typically 100–300 mm depending on structural zone; closer spacing at the pile head where bending moments are highest. Stiffener bars are welded at intervals per DIN EN ISO 17660 to maintain cage roundness and prevent racking during handling and installation.

Main Bar Diameters and Cage Configurations

For bored piles in the range 300–2500 mm diameter, main bars typically range from 16 mm to 40 mm. Spiral link diameters are typically 8–12 mm. Our B500B bar is available in diameters 8–40 mm, supplied in 12 m stock lengths or cut to project length. Where pile head to pile cap continuity reinforcement is needed, mechanical couplers (parallel-thread or taper-thread, dia 12–40 mm) eliminate the need for expensive lap lengths in congested reinforced caps.

Helical Links and Spiral Reinforcement

Spiral (helical) links are prefabricated from B500A coil stock — available in 6–16 mm diameters — and are the preferred confinement element for circular pile cages. Their continuous helix geometry provides superior concrete confinement compared to discrete hoops. Our coil stock is produced to DIN 488-3, with k ≥ 1.05 and Agt ≥ 2.5 %. For CFA piles where cage rigidity is critical (the cage must resist being unscrewed or rotated by auger withdrawal torque), closer helix pitch and additional stiffener bars are specified.

Standards and Design Codes for Pile Reinforcement

All material supplied by Steel Rebar Germany conforms to:

• DIN 488-1 to 488-6 — the German national reinforcing steel standard covering bars, coils, mesh and mechanical properties.
• EN 10080 — the harmonised European standard for weldable reinforcing steel, basis for CE marking.
• EN 1992-1-1 (Eurocode 2) — design of concrete structures, Chapter 9 covers detailing rules for pile reinforcement including minimum bar counts, concrete cover and link spacing.
• DIN EN ISO 17660 — welding of reinforcing steel (applicable to stiffener weld joints in cage fabrication).
• EN 1536 — execution of bored piles (European execution standard, references reinforcement requirements).

Concrete cover requirements for bored piles are typically 75–100 mm to the outer face of the helix, achieved using DIN 488 compliant concrete spacers. We supply DBV-type spacers and tying wire to complete the cage assembly package.