Geostress-associated settlements of a raft-foundation building due to shield tunnelling in soft ground

Abstract

Abstract The stress state of the soil, i.e., geostress, may affect the settlements of a building induced by the tunneling, which, however, has not been well understood. In this study, 3D numerical analyses combined with in-situ measurements were performed to investigate the geostress-associated settlements of a raft-foundation building due to shield tunnelling in soft ground. Basically, two types of geostress fields were investigated: the first type of geostress field considered the effect of additional stress generated in the foundation soil (FAS) due to weight of building; while in the second type of geostress field, a sequential twin tunnelling process was presumed, and the effect of the additional soil stress induced by the first tunnel (TAS) on the building response to the second tunnel was considered. The results indicated that the presence of FAS may aggravate the stress release of the foundation soil during a shield tunnelling, and thus gave rise to a larger building settlement or inclination. In a sequential tunnelling process, the effect of TAS can be more complex: when the first tunnel lowered the stress of the foundation soil, the TAS effect of the first tunnel may help reduce the building settlements induced by the second tunnel; otherwise, it may aggravate the building settlements. In addition to the TAS effect, the sheltering effect was also found to play an important part in the sequential twin-tunnelling. Especially when the first tunnel was positioned between the building and the second tunnel, the building settlements induced by the second tunnel can be impeded.