Timber pile groups — typical centre-to-centre spacing for design and driving What is a commonly adopted centre-to-centre spacing for timber piles in a group to ensure drivability, load sharing, and reasonable cap size (assume typical pile diameters)?

Introduction / Context:
Pile spacing affects group action, drivability, and pile cap economy. Too-close spacing risks pile-to-pile interaction during driving and increases negative group effects; too-wide spacing enlarges the cap and may reduce group efficiency minimally but at higher cost.

Given Data / Assumptions:

• Timber piles of typical diameters used in building/bridge works.
• Conventional group caps with reinforcement and practical driving tolerances.
• Soils where group action is relevant.

Concept / Approach:

Rules of thumb suggest spacing of about 2.5 to 3.0 times pile diameter (centre-to-centre) for friction piles; for small-diameter timber piles this often works out close to ~0.9 m. This spacing balances pile group effects and cap size while giving adequate room for driving and alignment tolerances.

Step-by-Step Solution:

Verification / Alternative check:

Design handbooks and standard drawings frequently show timber pile spacing near 0.9 m for small-to-medium diameters, with adjustments for soil type and cap geometry.

Why Other Options Are Wrong:

• 50–80 cm may be too tight for driving and risk excessive group interaction for typical diameters.

Common Pitfalls:

• Ignoring larger diameters or battered piles, which may call for wider spacing.
• Forgetting construction tolerances that require clear spacing between piles.

Final Answer:

90 cm.