Ground response to mini-tunnelling plus ground improvement in the historical city centre of Rome

The construction of a new underground metro line is being undertaken in thehistorical city centre of Rome. As part of the project, two tunnels will be excavated for a length of about 114 m following a three-step procedure: excavation of a small diameter tunnel with a mini slurry-shield machine; soil improvement via low-pressure cement grouting, performed radially from the mini-tunnels; and conventional excavation in the improved soil of the two tunnels of the line. The two mini-tunnels reach the San Giovanni station passing at a short distance from the ancient Aurelian Walls. The paper describes the results of the monitoring activity undertaken during the excavation of the two mini-tunnels and the cement grouting, focusing on observed field of ground displacements. Data are analysed to evaluate the volume loss induced by the mini-tunnelling and the soil heave induced by the low-pressure cement grouting.