Clearance allowed for pile diameter

[Kiri Robbie]

What clearance do you allow for the pile diameter compared to the steel reinforcing clearance? How parallel and straight are deep pile holes?

[Martin Larisch]

If you refer to the concrete cover zone for bored piles, they depend on your exposure class (how aggressive is your ground and ground water). Typically, cover zones are 50mm to 75mm for bored piles.

Plane installation tolerances are 75mm for onshore piles with cut-off levels within 2m below ground level. Vertical tolerances of 1 (H) in 100 (V) should be the industry standard for modern piling rigs. 

Reinforcement cages are normally parallel to the pile excavation. If the pile was installed at a very mild inclination of 1 in 100, the reinforcement would follow the same inclination as the cage is always parallel to the drilled hole.

Consideration of pile installation tolerances is critical for piled walls (e.g. secant piled walls) and for the assessment of additional bending moments from eccentricities.