Tunneling-induced sandy ground deformation affected by surface framed structures

The construction of urban subway tunnels will inevitably lead to ground movements and deformations, which are determined by the construction method and strata conditions and affected by the adjacent structures. Based on 24 centrifuge model tests, the influences of frame structures with raft foundations on the movement and deformation of dry sandy ground caused by tunnel construction are studied. Five aluminum frame structure models are manufactured, in which the length of the buildings, the width of the bays, the thickness of building elements and the number of stories are different. The influences of sand density, additional load of buildings and the relative horizontal position of structures and tunnel are considered in the tests. In the centrifugal tests, the displacement data of the soil and buildings are captured by particle image velocimetry technique. The horizontal and vertical displacements of the surface soil, the movements of ground and the contour of shear and volumetric strains are released. The results show that the surface frame structures have a great influence on the horizontal movement of the soil, the central long buildings significantly restrict the horizontal movement of the shallow soil, and the degree of restriction is related to the building load and the size of the gap between rafts and ground surface, while the eccentric short buildings increase the horizontal movement. The structural load widens the ground settlement field, and the degree of influence increases with the increase of building load. The restriction of the foundation to the horizontal movements of soil generally results in a thin shear band at the soil-foundation interface with a decreased maximum contraction level. The relative expansion index of sand depends on the relative density and stress state. Therefore, for the loose soil tests, the loose sand exhibits a contractive response, whereas the dense soil transforms from contractive at lower values of tunnel volume losses towards dilative at higher tunnel volume losses. The building load slightly increases the contractive deformation of the soil. The research results may provide important reference for safety assessment of nearby buildings and risk control of shield tunnel construction in urban areas.