The world of underground engineering and construction has acquired a wide-ranging and high-level experience on tunnel construction with Tunnel Boring Machines (TBM), thanks to the remarkable increase in the number of tunnels that are becoming longer, going deeper, and growing larger in diameter; in other words, becoming more diffi cult to realize.
In urban areas, the acquired consciousness of preservation and care for the anthropogenic environment, accompanied by the improvement in the quality of life, has raised the level of diffi culty and challenge in respecting the constraints deriving from human presence and, therefore, the necessity for a technological and intellectual approach to respond appropriately to these constraints.
This recent, invaluable experience gained from a series of accidents in urban tunnelling worldwide has made us aware that the TBM is simply not a fully mechanized tool integrating the various operations of the conventional excavation method for excavating more rapidly, and overcoming all (or almost all) the well-known problems and uncertainties. Instead, the TBM and the tunnel to be excavated, constitute a delicate and sensitive, unitary system, which should be managed with a new approach, rationally organized and scientifi cally sustained, in a unifi ed context of research and design of the tunnel, the machine, and the environment.
In particular, all the principal risk factors are found to be associated with tunnels in densely populated urban areas, including the properties and services subject to risk, poor geotechnical conditions of the ground, presence of and consequent interference with water table, and the small overburden with respect to the excavation diameter. The focus of this book is exactly on the problems of urban areas.
Its authors want to analyze and propose not only the machines, but also, above all, the new special techniques for controlling the proper operation of machines and, consequently, the ground water drainage, the stability of the excavation face, and the resulting tunnel profi le, for the purpose of minimizing the risks of subsidence. Therefore, a substantial portion of the book is dedicated to identify, evaluate, and manage such risks.
Framed in this particular manner, it seems to me that the book stands up above customary texts, in drawing attention to mechanized construction of tunnels in urban areas as a complex system that needs real or conceived certainties: adequate preliminary investigations for small depths must supply exhaustive information; scientifi c design that should not leave anything to be invented during construction.
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