Deep Tunnel Excavations Using Tunnel Boring Machines

摘要

An analysis related to the experience of the authors regarding tunnels with limited overburden and on the basis of an examination of case-histories from literature on deep and long tunnels has been carried out in this paper. At present, as is known, there are only a few of these tunnels, the most important being the Loetscberg tunnel, which has just been opened.The question that can be asked is whether the experience gained in the excavation of tunnels with limited overburden could be extended to deep and long tunnels.Some studies that have recently appeared in literature seem to confi rm the infl uence of tunnel-face stress confi nement, due to the depth of the tunnel, on TBM performance.After the description of the performances of TBMs in some short tunnels with low or medium overburden, this paper takes into consideration the experience gained in the past and more recently in long and deep tunnels excavated by TBMs.The concluding remarks point out the necessity to take into account particular phenomena, such as rock burst and squeezing, to correctly forecast the TBMs performances in deep and long tunnels. In particular, the Utilization Coeffi cient of the machine should be estimated considering the tunnel depth and the thrust force applied to disc cutters, in order to make a correct choice of the excavation method (D&B or TBM) for long and deep tunnels, especially when hard rocks and diffi cult ground conditions are expected.