Definition - What does Launch Seal mean?
A launch seal, also known as an entrance seal, is a rubber flange attached to the wall of the jacking shaft.
As the microtunnel boring machine (MTBM) moves forward, it distends the flange and prevents the flow of groundwater or lubrication into the shaft while tunneling operations are in progress.
Trenchless technology has made it possible to install pipelines without excavation but has its own challenges to overcome. A launch seal is a perfect solution to maintain suitable sealed ground conditions for the tunneling process.
Trenchlesspedia explains Launch Seal
While constructing a tunnel, one of the most critical phases is the interface between the MTBM launch shaft and the tunnel excavation. This area is often at high groundwater pressure. To prevent ingress of groundwater and material into the shaft, a launch seal is installed to prevent consequent ground loss.
The launch seal consists of a gasket system with a pair of lip seals for the shield front and a hose seal at the shield tail. This gasket system is installed in the sealing ring and sealing soil at the base of the shaft behind the retaining wall.