Ricerc@Sapienza

Over the last decade several tunnel excavations in difficult conditions were successfully performed using TBM-EPB technology with the help of soil conditioning agents that, in fine-grained soils, have proved to be particularly effective in reducing the clogging risk.
TBM excavation performances are strictly related to the management of the injection of these products. Consequently, a preliminary study on the typologies and dosages of chemicals required to reduce the clogging risk in the soil to be excavated has become a key component of good tunnel design.

The most effective, safe and controlled way to perform tunnel excavations is through the use of Tunnel Boring Machines. This technology often requires the injection of chemicals to modify the soil properties, enhancing the control on the pressure applied at the front-face and consequently reducing the risks related to unexpected surface settlements, to excessive abrasion of the excavation tools and to clogging phenomena inside the working chamber.

The use of Tunnel Boring Machines (TBM) and particularly the Earth Pressure Balance (EPB) technology is one of the most commonly used way to perform mechanized tunnel excavation. The possibility to perform the excavation with high performance, avoiding risk for workers and reducing the induced subsidence, particularly important in urban area, are the main reason of the growing of this technology.

Earth Pressure Balance (EPB) technology is currently the most widely used technique in mechanized tunnelling with Tunnel Boring Machines (TBMs) and particularly in urban en-vironments, because of several advantages, as the possibility to excavate in different geo-logical conditions and effectively controlling the induced effects on the pre-existing struc-tures. EPB technology requires the continuous injection of chemicals during the advance-ment: this may induce the accumulation of xenobiotic compounds in the excavated debris.

During tunnel excavation with Tunnel Boring Machines (TBMs) and earth pressure balance (EPB) technology, conditioning agents are commonly used to modify the physical and mechanical properties of soils so that they are appropriate for the application of the front-face support pressure during excavation. The consistency of the conditioned soil must be stable during the time necessary to advance and install the lining. Hence, a stability analysis of the injected foams is an important aspect.