North American Society for Trenchless Technology

Glossary of Terms
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Term	Definition
Narrow trenching	Method of excavation of a trench up to 100mm wider than the outside diameter of the service to be installed, usually employing either a rockwheel or chain type trencher.
Neutral axis	An axis of no stress.
Nominal size	Size of pipe or shaft used to define the internal working diameter.
Nominalize	To classify a value into an established range or category.
Non-man entry	Size of pipe, duct or bore less than that for man-entry.
Non-uniform corrosion	Corrosion that attacks small, localized areas of the pipe. Usually results less metal loss than uniform corrosion but causes more rapid failure of the pipe due to pits and holes.
Notch sensitivity	The extent to which an inclination to fracture is increased by a notch, crack, scratch, or sudden change in section.
Notice of award	The written notice by owner to the apparent successful bidder stating that upon compliance with the conditions precedent to be fulfilled by him within the time specified, the owner will execute and deliver the agreement to him.
Notice to proceed	NTP, a written notice given by the owner to the contractor (with a copy to the engineer) fixing the date on which the contract time will commence to run and on which contractor shall start to perform his obligations under the contract documents.

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