3D numerical modelling of a compensation grouting field trial in alluvial soils

The underground bypass of the new high-speed and high-capacity railway line in Florence (IT) involves the construction of about 7 km of twin tunnels beneath the historic city centre. To minimise the impact of tunnelling works, mitigation measures using the compensation grouting technique were integrated into the design stage with the aim of limiting the induced settlements and the risk of damage to nearby structures. A field trial near the Campo di Marte railway station was carried out to assess the efficiency of the compensation measure and establish a successful grouting strategy. This paper presents a three-dimensional numerical model of the field trial, explicitly implementing both the grouted volumes and the injection sequence. The grouted area is represented by non-porous soil bulbs with enhanced stiffness properties and the expansion process is simulated through imposed volumetric strains. The injections from each valve of the sleeved pipes (tubes-à-manchettes) are activated in a stepwise procedure, mirroring the injection sequence. The effectiveness of the proposed strategy is validated against recorded displacements in the field trial, demonstrating that the application of non-isotropic volumetric strains (i.e., vertical strains larger than horizontal ones) is able to accurately reproduce the observed heave.