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September 05, 2019

Study for the Compensation Grouting: The Case of the Underground Railway of Florence

P. Cucino, S. Fuoco, D. Maniezzo

SWS Engineering S.p.A., Trento, Italy



A new underground link is under construction in Florence and connects the existent FlorenceRome railway track to the new high speed railway line from Florence to Bologna. This connection will be almost totally underground in urban areas, and it has an overall length of approximately 6 km (Fig.1) with a cover thickness from 5 m to about 26 m. The new railway station is going to be located along the link track almost in the middle of the path. The settlements due to the tunnel excavation will be constantly monitored: special compensation techniques have been studied to avoid any damage to the buildings in the areas surrounding the tunnel, with particular regard to historical buildings. Nowadays the choice of the best injection technique, appropriate mixture quantity, order and number of grouting ports, is principally demanded to operators experience and know-how which results hard to transfer from one to another. The numerical study (performed by means of a 3D design software) summarized in this paper shows the effects which some key features have on compensation procedures. This study reproduced excavation advance simulating the EPB shield, surface settlement and ground reaction to compensation grouting. The results obtained from the numeric model represent a valid reference to esteem, for the simulated boundary condition, the influence of grouting on superficial subsidence field. Furthermore, the study defines an analytic procedure to design compensation grouting with regard to mixture quantity and quality, procedures and sequences to be applied for execution and defines a meaningful performance parameter to be used for design."


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