Pile spacing guideline – friction piles: For friction piles of 1.0 m diameter, what is the typical minimum centre-to-centre spacing recommended in practice?

Introduction / Context:
Pile spacing affects group efficiency, construction feasibility, and soil–pile interaction. Friction piles transfer load largely through shaft resistance, so keeping adequate spacing minimizes overlap of stress bulbs and simplifies reinforcement and head connection details.

Given Data / Assumptions:

• Pile type: friction piles (skin-friction dominant).
• Pile diameter: 1.0 m.
• General practice values without site-specific group interaction analysis.

Concept / Approach:
Rules of thumb: end-bearing piles are often spaced at about 2.5d to 3.5d; friction piles typically need slightly larger spacing to reduce interaction but still often fall within 2d to 3d minimums for constructability and load transfer, unless rigorous analysis dictates otherwise. Many codes and handbooks cite minimum center-to-center spacing ≥ 2.5d, but ranges of 2d to 3d are commonly accepted for preliminary layout.

Step-by-Step Solution:

Verification / Alternative check:
Detailed group efficiency analyses (e.g., Converse–Labarre) or numerical models often validate preliminary spacings in the 2d–3d range for friction piles unless constrained by geometry or high loads.

Why Other Options Are Wrong:

• 2.0 m (exactly 2d) may be acceptable as an absolute minimum but lacks the typical range context.
• 3.0–4.0 m and 5.0 m are not “minimum” values; they may be used but are not minimal practice guidelines.

Common Pitfalls:
Ignoring group effects in soft clays; using too-tight spacing that complicates construction or reduces efficiency; forgetting to check pilecap geometry and reinforcement congestion.

Final Answer:
2.0 m to 3.0 m