Superposition behaviour of ground settlements caused by symmetrical deep excavations in soft soils

The aim of this paper is to investigate the ground settlement caused by two symmetrical deep excavations in soft soils. The ground settlements under excavation procedures and distances were investigated using the finite-element method and centrifugal model testing. Testing results show that when two symmetrical pits are excavated successively, the ground settlement exhibits a non-linear superposition. The superposition factor of the ground settlement at the symmetrical centre follows a quadratic parabolic function change. When excavated simultaneously, the ground settlement increases non-linearly with time, and the magnitude from the symmetrical centre to the edges of the two excavations decreases with increasing distance. The ratio of the ground settlement at the centre of the two symmetrical excavations caused by simultaneous excavations and single excavation shows a power function-like behaviour. The ground settlement caused by successive excavations is higher than that of simultaneous excavation, and the ratio of ground settlement under the two excavation conditions increases with increasing distance. Simultaneous excavations have priority over symmetrical excavations because of their better settlement control capability. Stricter settlement control requirements should be raised under successive excavation, and the distance between the second excavation and the bearing platform should be larger than 1.0H (depth of deep excavation).