Pile Foundations Guide: Driven, Bored, and CFA Compared

When ground conditions can't support a building on shallow foundations, piles transfer load down to stable strata. The method matters — wrong choice costs weeks and tens of thousands.

When piles are needed

• Made ground or poor surface soils
• High water table
• Heavy structures on average ground
• Sites near trees on shrinkable clay
• Brownfield sites with mixed fill
• Tall buildings requiring deep load transfer

The main pile types

Driven precast concrete

Precast concrete sections hammered into ground. Fast, reliable on greenfield.

• Cost: R1,600–R3,000 per linear metre
• Pros: Fast, high capacity, well-understood
• Cons: Noisy and vibrates ground — unsuitable near sensitive buildings

Bored cast-in-place

Hole is augered, reinforcement placed, concrete poured.

• Cost: R2,000–R4,000 per linear metre (small) to R8,000+ for large diameter
• Pros: Quiet, variable depth, can handle obstructions
• Cons: Slower than driven, requires temporary casing in unstable ground

CFA (Continuous Flight Auger)

Auger drilled to depth, concrete pumped through hollow stem as auger withdraws.

• Cost: R1,500–R2,800 per linear metre
• Pros: Quiet, fast, suits urban sites
• Cons: Limited inspection of pile shaft, less effective in cohesive clay

Mini-piles

Small-diameter piles (150–300 mm) installed with compact rigs.

• Cost: R3,000–R5,000 per linear metre
• Pros: Restricted-access sites, low headroom, low vibration
• Cons: Lower capacity per pile, more piles needed

Screw piles

Helical steel piles screwed into ground.

• Cost: R3,000–R5,600 per linear metre
• Pros: Fast, no spoil, removable
• Cons: Limited capacity in soft ground

Pile cap design

Piles connect to the structure via reinforced concrete pile caps. Cap size depends on pile diameter and structural load — typically 1.5–3.0 × pile diameter wider than the pile head.

Pile testing

Required on most schemes:

• Static load test — applies load and measures settlement. Most reliable, expensive (R60,000–R200,000 per pile)
• Dynamic test — uses pile-driving energy. Cheaper, less precise
• Integrity test — sonic echo on a percentage of piles to detect defects

Choosing the method

Selection driven by:

• Ground conditions (made ground vs natural)
• Access (urban infill vs open site)
• Loads to carry
• Sensitivity to vibration/noise (heritage neighbours)
• Programme

MCFAR designs piled foundations across South African projects.

Frequently Asked Questions