ENEL - Linee guida gallerie con TBM
In the last 60 years the excavation methods varied greatly, mechanized tunneling bringing significant progress to the safety and quality of the final product and the execution rate. The design approach extends more than the evaluation of the overall rock or soil conditions and characteristics, the subsequent convergence-confinement behavior or rock wedges (deep tunnels) and chimney-silo-caving risks and relevant loads (shallow tunnels). The risks involved by mechanized excavation become more visible with the time passing, for more complex and difficult conditions are often to be crossed by the more recent projects. The selection of the suitable method is a challenge for the designer, confronted not only with the geological, hydrogeological and geotechnical aspects for selecting the suitable countermeasures but adjusting the work progress to the variations of the local conditions. By mechanized methods, these adjustments can be only limited. Therefore the design good for construction should represent the suitable balance between an economical construction approach and the need for assuring the successful crossing of all the conditions foreseen to be encountered, in their worst expression. The thoroughly analysis of the known conditions is then to be supported by a risk analysis focused to the critical verification of "what/if" situations in order to assess the completeness of the design and to determine if and at how contingency measures and residual risks are to be considered for the construction and for financial or insurance allocations. In all this, collateral aspects such as the logistics (accesses, supply lines/times and possible emplacement of the support installations) and the human factors (experience of the contractor and general construction culture at the project location) become significant aspects, possible to be killer factors for a solution by mechanized tunneling.
The task is the formulation of a guideline through this process, for allowing the selection of the most suitable excavation method or methods in a given project layout and conditions.
Enel Green Power S.p.a. - Roma
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