The response of framed structures to tunnelling: experimental results, numerical assessment, and monitoring evidence

The paper summarises a series of research studies aimed at investigating the response of framed structures to tunnelling in coarse-grained soils. The activities were developed with a twofold objective: on the one hand, an extensive experimental campaign of centrifuge tests was designed and carried out in order to obtain a consistent set of data, although for simple geometric configurations of the structure and of the tunnel-to-structure relative position; on the other, attention was paid to the essential elements to be included in the numerical simulations, essentially in terms of tunnel excavation simulation procedures, adopted detail in the schematisation of the structural components and constitutive laws to describe the non-linear soil and structural response. Validation of numerical models, based on experimental results, allowed them to be used to extend the analysis to further configurations and to fully define the modification factors of the maximum angular distortion of the span as a function of the relative soil-structure shear stiffness. In addition to the direct comparison with the centrifuge data, the numerical strategy was also validated against in situ observations carried out over a stretch of the Milan metro line 5. This case study was also used to perform a numerical exercise, through inverse analysis and meta-modelling procedures, to optimize the position of the monitoring sensors for a possible real-time calibration of the soil constitutive and TBM-EPB machine parameters used in the numerical modelling.