Tunnel

An underground conduit, often deep and expensive to construct, which provides conveyance and/or storage volumes for wastewater, often involving minimal surface disruption.

Tunnel Boring Machine (TBM)

(1) A full-face circular mechanized shield machine, usually of Man-EntryDescribes any trenchless technology process which requires an operative to enter a pipe, duct or bore. OSHA has no minimum size limit for Man-Entry; however, they address a much broader concept of "confined space" in Title 29 Code of Federal Regulations Part 1910.146. The minimum size for which this is permissible in the UK is 900 mm (approximately 36 in.). diameter, steerable and with a rotary cutting head. For pipe installation it leads a string of jacked pipes. It may be controlled from within the shield or remotely. (2) (MoleSee Impact Moling., TunnelingA construction method of excavating an opening beneath the ground without continuous disturbance of the ground surface and of large-enough diameter to allow individuals access and erection of a ground support system at the location of material excavation. Head) A mechanical excavator used in a tunnel to excavate the front face of the tunnel.

Tunnel Horizon

The vertical band within the ground where the tunnel is excavated. Includes one tunnel diameter above the crown and one tunnel diameter below the invert.

Tunneling

A construction method of excavating an opening beneath the ground without continuous disturbance of the ground surface and of large-enough diameter to allow individuals access and erection of a ground support system at the location of material excavation.

Two-Pass

A procedure by which the carrier pipe is installed within a casing.