Definition - What does Entrance Seal mean?
An entrance seal is a rubber flange fixed to the jacking wall during the operation of a microtunnel boring machine. It is used to prevent slurry and groundwater from blowing back into the entrance pit.
An entrance seal is also known as a launch seal, or launching seal.
Trenchlesspedia explains Entrance Seal
A microtunnel boring machine is often used in soil with high groundwater, and it is also used for the excavation of tunnels beneath waterways. Because of the presence of water and the use of a slurry system, it is necessary to create a barrier to keep these fluids from flowing back into the entrance shaft.
The entrance seal is installed onto the jacking wall and surrounds the pipe to create a watertight seal. It may be attached to a concrete wall that has been constructed around the entrance or a metal plate attached to the jacking wall. The entrance seal is designed to maintain its seal despite the constant movement of the jacking pipe through the borehole.