Role of tunnel ground loss on the mitigating effect of pile-wall barriers

Pile wall barriers are an effective mitigation measure to protect heritage or infrastructure from tunnelling-induced ground movements. This paper presents the results of parametric finite element analyses aimed at studying the effect of tunnel volume loss on the efficiency of end-bearing pile wall barriers, accounting for shearing at the soil-pile interface. The considered scenario is the field trial of a pile wall barrier installed at an experimental site during the construction of the Line C of Rome underground railway. Results indicate that, at small volume loss, the excavation induced movements can propagate across the barrier. Contrarily, at larger applied tunnel volume loss, shearing at the pile interface, enhanced due to the barrier embedment in the stiff bottom layer, results in the progressive formation of a slip plane that prevents the transmission of soil displacements behind the wall, thus acting as a smooth continuous diaphragm wall. The transition from perfect compatibility to slipping between the soil and the barrier affects the propagation of the ground loss, and hence surface settlements, on both sides of the wall.