In this type of drilling, the pipe is used as a final element of the tunnel and at the same time during the advance must be able to transmit the pushing force to the TBM (Hydroshield, EPB or open shield).
The advance is made through the push made by a set of main jacking cylinders intalled in the starting shaft on the jacking pipe. This pipe has been manufactured in accordance with strict rules, in order to withstand great efforts longitudinal and transverse without suffering any damage.
The pipe pushed by the jacking frame will build the final tunnel once the drive is finish. In the conection between pipe there is a joint which must guarantee the tightnes. Also there is a woden plate between concrete pipes which absorbs any irregularities in the pipe and allowing this will not get damaged during the pushing.
A wall reaction must be built in the starting shaft that must support the thrust forces for the advance, and an ending saft must be build to rescue de machine. For long drives, interjack stations are installed between the pipes that allowe to distribute the efforts among several sections…” – Eurohinca website.