Performance of a deep excavation for the new line C of Rome underground

The construction environment of tunnels and deep excavations is often very complex because of the presence of pre-existing buildings, often of historical or architectural value. Therefore, the accurate control of excavation stages and the use of intense monitoring for early warning of potential damage is essential to ensure that nearby structures would not be affected by ground deformation. This is particularly relevant for the city of Rome, where a new metro line is being constructed in the historical city centre, facing significant problems for the presence of archaeological artefacts and for the necessity of minimising the effects on the historical and monumental heritage. This paper describes the field performance of a 30 m deep excavation which has been constructed at short distance from the ancient masonry walls of the city, the Aurelian Walls of Roman age. An extensive instrumentation program was conducted during construction. Field observations included deflections of diaphragm walls, ground displacements, pore water pressures and settlements of surrounding buildings and those of the city walls. Analyses of field data indicated that ground settlements and diaphragm wall deflections were smaller than those observed in other case histories worldwide, with only negligible effects observed in the Aurelian Walls.