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The C Line of the Rome underground underpasses the historical city center, facing significant problems for the presence of archaeological artefacts and the necessity to prevent damage to the historical and monumental heritage. This paper describes the field performance of a 30-m-deep excavation that has been constructed at a short distance from the Aurelian Walls at Porta Asinaria (third century). An extensive instrumentation program was conducted during construction, as well as field observations including deflection of the diaphragm walls, ground movements, pore water pressures, settlements, and rotation of the Aurelian Walls. Observed ground settlements and diaphragm wall displacements were smaller than those monitored in other case histories worldwide, inducing no damage to the Aurelian Walls. The lessons learned from this case study showed that a stiff retaining system and a strict control of the construction sequence were the key to minimize the effects of a deep excavation with millennia of history at risk. [ABSTRACT FROM AUTHOR]

Compensation grouting is often employed as a mitigation technique to reduce the settlements induced by tunneling. The efficiency of compensation grouting, defined as the ratio of the volume of heave induced at the ground surface to the volume of injected grout, is strongly dependent on grout properties, injection characteristics, and soil properties. In clayey soils, site observations and laboratory tests show high values of compensation efficiency immediately after injection. However, the efficiency can decrease with time if positive excess pore-water pressures develop in the soil during the injection process. Conversely, in sandy soils, a loss of volume occurs because of pressure filtration of the grout during and soon after the injection process, which reduces the compensation efficiency. This paper describes an analytical model that can be used to evaluate the volume loss produced by pressure filtration of cement-bentonite grouts as a function of soil, grout, and injection parameters. The magnitude of pressure filtration is evaluated as the grout efficiency, which is given by the ratio of the volumes of the final grout body to the injected grout. Results show that the grout efficiency increases with decreasing soil permeability and with increasing grout bentonite content. The result of a grout injection test on a silty soil is back-analyzed using this approach in which the grout efficiency is first evaluated through the proposed filtration model and then used to calibrate a numerical simulation of the test. The good agreement between experimental data and computed results shows that prediction of the efficiency of compensation grouting can be improved using the proposed approach. [ABSTRACT FROM AUTHOR]