The Influence of Construction Scheme of Asymmetric Three-Cabin Utility Tunnelling on the Surface Settlement Behaviour

摘要

The asymmetric three-cabin structure is one of the favourite choices in urban utility tunnel engineering, as it can provide a higher space utilization and clearer classification for pipelines. However, few work has been done on utility tunnel in such special cross-section during undercutting construction until now. Besides, as the loose soil layers such as sand and silt are often encountered during the utility tunnelling, its influence on surface settlement become one of the main concerns. This study focuses on the influence of the construction scheme on the surface settlement details for an asymmetric three-cabin utility tunnel. A 3D finite element method (FEM) model was established including both the stratum and a utility tunnel based on the Beijing Daxing International Airport (BDIA) Expressway Urban Utility Tunnel project. With this model, the behaviour of the surface settlement with the undercutting construction of the utility tunnel was investigated, and the causes and values of surface settlement in five construction stages were analyzed. By changing the construction spacing and sequence of mid and side cabins, the surface settlement and structural deformation were compared. The numerical results demonstrated a strong correlation between the cross-section shape and surface settlement characteristics. And the symmetry line of the surface settlement trough was offset by 1 m to the side with the larger cross-section. The second (excavation of upper bench in mid-cabin) and fourth (excavation of upper bench in side-cabin) stages caused the largest surface settlement, which were 41.9% and 18.07% of the total settlement, respectively. In addition, after optimizing the field tunnelling scheme, the surface settlement was reduced by 31.9% using the side-tunnel first construction sequence. The proposed numerical model is able to predict the settlement characteristics in each construction stage, which is important and provides a basis for further studies on the surface settlement mechanism and optimal design of the asymmetric three-cabin utility tunnelling scheme.