What Does Exit Seal Mean?
An exit seal is similar to a launch seal and is installed for the purpose of machine retrieval at the reception shaft. It is used where groundwater level is high and soil is unstable. An exit seal helps to prevent ground loss and entry of water and soil into the shaft.
A microtunnel boring machine (MTBM) is operated by remote control and requires suitable ground conditions for operation.
Trenchlesspedia Explains Exit Seal
Exit seals are installed at the reception shaft for receiving the machine as it exits the borehole. The seal is mechanical in nature and is composed of a rubber flange mounted to the wall of the drive shaft. As the MTBM progresses it distends the flange creating a watertight seal that prevents water or lubricant from flowing into the shaft.
The exit and entry seals are designed to withstand expected hydrostatic and slurry pressures while launching the machine, during the tunneling operation and once the tunneling is complete. The main purpose of the seals is to prevent Ingress of pressurized groundwater, soil and slurry into the reception shaft.