EPB, mix shield and variable density (VD) – Where are we today with soft ground TBM?

EPB, mix shield and variable density (VD) -Where are we today with soft ground TBM? EPB, Mixschild und Variable Density (VD) -Wo sind wir heute bei den Lockergesteins-TBM?Today, deciding on the machine concept for tunnelling in soft ground is no longer simply a matter of choosing between earth pressure shields (EPB) and slurry shields (Mix/Slurry).Since the market launch and first use of Variable Density (VD) TBMs in Kuala Lumpur, these machines have been further developed and subsequently used on various tunnel projects worldwide, leading to the current state of the art.In this article, we compare the three machine concepts Mix/Slurry, EPB and VD with regard to the following selection criteria: geology with torque requirement, clogging, settlement, material transportation and disposal, face support, chamber access and re-start.We highlight the differences and opportunities presented by these different concepts and finally, present the outlook for the future based on the current state of technology.