Numerical investigation into the influence of cross walls on a deep excavation

The growing population in metropolitan areas has driven the need for enhanced infrastructure, often requiring deep excavations near buildings and monuments. A primary challenge is minimising displacements during and after excavation, which can be addressed through effective design solutions and displacement mitigation systems. In this framework, the cross-wall system has been successfully employed in cities over the world and mainly in Asia. The system involves pre-installed cross walls that work as pre-embedded struts on the excavation side, reducing the displacements of the diaphragm walls and limiting settlements during excavation. Cross walls also improve the stiffness of the soil beneath the excavation bottom, reducing excavation heave caused by the relief of vertical stresses. This paper presents a numerical study that evaluates the efficiency of various cross-wall systems, based on the available soil profile and geotechnical characterisation data for Venezia station on Line C of the Rome underground. 3D Finite Element (FE) analyses were first conducted on a reduced numerical model simulating the diaphragm walls and the cross walls as cluster elements, to calculate the displacement field induced by the excavation. A simplified 3D FE model, in which plate elements were used incorporating anisotropic stiffness for the diaphragm walls, was then calibrated for further investigation. The efficiency of the cross-wall system was then assessed, also considering the partially drained conditions in the presence of cross walls, which have not been explored in the literature so far. A comparison with existing literature data finally validated the findings of the study.