Earth pressure balance tunnelling in rock masses: Laboratory feasibility study of the conditioning process

Earth pressure balance (EPB) shield tunnelling is considered to be an effective tunnelling method when surface settlements must be avoided by controlling face stability and underground water inflow. EPB technology is applied increasingly to the conditioning of rock masses in which the presence of polluting material is foreseen and must be controlled, or when explosive gases from the rock mass must be prevented from entering in the machine. The use of an EPB machine in ‘closed mode’ can prevent the dispersion of dangerous materials in the underground environment. This study was performed to evaluate the feasibility of using EPB technology in rock masses and the effectiveness of this tunnelling process in terms of soil conditioning, conditioned soil permeability, pressure transmission on the tunnel face, and the ability to extract the material with a screw conveyor. The research was developed with a set of laboratory tests carried out on three different types of rock masses where tunnelling with EPB machines are planned to be constructed in Italy but the results can be easily applied to similar rock mass types. The tests have been carried out both with slump tests and with a specially constructed screw conveyor extraction device. In the paper the most important results are presented and discussed.