Disassembly of false tunnels
There is always a false tunnel, around 7 rings long, between the push frame and the diaphragm wall. We will always find at any TBM launch.
Besides, when TBMs have to cross short ventilation shafts, it is easier to advance TBM assembling the whole rings, than install a push frame.
Then, we can also find false tunnels in intermediate shafts.
In addition, depending of the project time schedule, sometimes the tunnel advance is faster than the building of stations. There are projects where it has been necessary to dismantle the tunnel rings in order to build the station.
The demolition of segments is the easy way to dismantle false tunnels, but it interrupts the tunnel activities during some weeks.
Instead, by disassembling the rings in whole segments, without demolition methods, this activity can be done without many affection to the tunnel activity. Moreover, it can be done in stages, coordinating with foreseen TBM stops.
Each project requires an accurate analysis, where the needs and the means have to be taken in account.
We have obtained good results using this methods while the tunnel was still in service for TBM advance.