Deformation of adjacent buildings and ground settlement induced by shield construction of three-line small-spacing tunnels

Abstract

Metro tunnels are often constructed between dense building foundations and underground pipelines, thus the spacing between adjacent tunnels is usually small. A decrease in the spacing can significantly increase the severity of tilting of adjacent piles or ground settlement on either side of the metro. In order to analyse the settlement response of the ground surface and adjacent buildings, as well as the movement of the building piles, field monitoring and numerical simulations were carried out for a section of three small-spacing tunnels. A three-stage analysis method was proposed for the calculation of the ground settlement curve induced by the excavation of the three-line tunnels. The results show that the construction of the three-line small-spacing tunnels caused significant tilting of neighboring piles. Furthermore, the excavation of a new tunnel near the completed tunnel extended the area of settlement, thus increasing the possibility of tunnel construction affecting the adjacent buildings and piles. The maximum axial stress increased as the excavation face approached the pile when the distance reached 4D (D is the diameter of the tunnel), then it stabilized when the excavation face passed a distance of 2.5D. As the excavation face approached the pile, the settlement of the pile top gradually increased and stabilized after passing a distance of 8D. The horizontal displacement of the pile bottom reached stability when the excavation face passed a distance of 2D.