Entrance Pit

1) An opening in the earth of specified length and width for placing the machine on line and grade. 2) See Boring PitAn excavation in the earth of specified length and width for placing the machine on line and grade..

Entrance Seal

See Launch SealA mechanical seal, usually consisting of a rubber flange that is mounted to the wall of the jacking shaft. The flange seal is distended by the MTBM as the machine passes through the shaft. The seal is intended to prevent the flow of groundwater, soils, slurry, and lubrication into the shaft during tunneling operations..

Entry Ring

See Launch Seal.

Entry/Exit Angle

Angle to the ground surface at which the drill string enters or exits in forming the pilot bore in a directional drilling/guided boring system.

Environment

The surroundings or conditions (physical, chemical, mechanical) in which a material exists.