The following tolerances shall apply to trenchless construction:
- Invert Levels
The permissible deviation from the designated level of the invert at each manhole or structure shall be ±50mm, provided that the fall between successive manholes or structures shall be at least 90% of that specified.
- Horizontal Alignment
The permissible deviation of the horizontal alignment between manholes or structures shall be ±100mm.
For straight gradients, the permissible deviation from the specified gradient shall be ±50mm from a straight line drawn between the inverts of successive manholes, provided that no point in the pipeline is lower than any downstream point. For curved gradients, the curvature shall be in the direction of the specified curvature and no point in the pipeline shall be lower than any downstream point.
Directional drilling only:
Annulus: 0 – 25mm between slurry and hole
Back ream diameter: Pipe diameter + 25% minimum, + 50% maximum