https://www.forrestfieldairportlink.wa.gov.au/construction-sites/...

https://www.forrestfieldairportlink.wa.gov.au/construction-sites/emergency-egress-shafts

Cross passages
The cross passages are located at numerous points along the route to provide a connection between the tunnels. In the unlikely event of an emergency, passengers will be able to exit the train and use the tunnel walkways to locate the nearest cross passage. They will then be able to enter the adjacent tunnel safely and exit through the nearest emergency egress shaft, station or dive structure.

Cross passages are constructed using the jet grouting process, a construction technique used to improve ground conditions and stabilise soils in preparation for tunnelling works.


....”Failure mechanisms can be classified according to three different modes: excavation face failure, canopy tip failure, provisional lining failure. With regard to the control of settlements, jet grouting has proven to be very effective but some ground uplift can be temporarily induced by soil treatment.
(PDF) Jet-Grouting Performance in Tunnelling. Available from: https://www.researchgate.net/publication/268590279_Jet-Grouting_Performance_in_Tunnelling[accessed Sep 26 2018].