Tunnelling in urban areas by EPB machines: technical evaluation of the system

The paper refers to the methods adopted for building a high-speed railway tunnel system between Bologna and Firenze
(Italy), focusing attention on the Bologna node which represents the heart of the system, connecting the high speed
network’s main lines. The project includes 9 tunnels, accounting for 73 km of the 78 km route crossing below the
Apennines. The paper pays attention to the main aspects to be taken into consideration for correctly choosing the tunnel
boring machinery (
TBM) tobe used in urban areas. Thefundamental point in analysing technical aspects regarding an earth
pressure balance (
EPB) machine concerned storing the main excavation parameter values; having collected and organised
such data, statistical methods were used for processing it, the instantaneous velocities attained were empirically estimated
and idle times were evaluated. The evaluation was made by calculating excavation specific energies (during different
excavation phases) to find a satisfactory correlation with the type of ground crossed. Interesting results have been found by
comparison with other excavation parameters; in particular, a better understanding of an earth pressure balance shield’s
working phases has been reached thanks to an experimental study conducted during the construction of tunnels for a
high-speed railway system in Italy. The paper contains details collected regarding the operation of two different EPB
machines.