North American Society for Trenchless Technology

Glossary of Terms
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Term	Definition
Ultraviolet Absorbers (Stabilizers)	Compounds that when mixed with thermoplastic resin selectively absorb ultraviolet rays protecting the resins from ultraviolet attack.
Uncased bore	Any bore without a lining or pipe inserted, i.e. self-supporting, whether temporary or permanent.
Underdrain	See subdrain.
Underground utility	Active or inactive services or utilities below ground level.
Uniform Corrosion	Corrosion that results in an equal amount of material loss over an entire pipe surface.
Upset	The inadvertent action of a boring machine that rotates the machine and track from its normal and upright position to another position.
Upsizing	Any method that increases the cross sectional area of an existing pipeline by replacing with a larger diameter pipe.
Utility corridor	Duct in which two or more different utility services are installed with access for maintenance. Commonly referred to as a Utilidor in North America.

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