LAUSR

Demands for underground space (e.g., metro stations, deep basements, and underpass) in congested urban areas have been increasingly growing in recent years. The top-down excavation technique becomes an attractive alternative compared to the conventional cut-and-cover construction method, as the ground traffic can be disrupted for a much shorter period. In this investigation, an underpass project linking two large-scale basements under heavy ground traffic constructed by the top-down approach is introduced. The specialty of the project is that the geometry in plane is irregular, which makes the excavation challenging since all empirical design criteria cannot be applied directly. The lateral supports are not applied all around the perimeter of the excavation (only two short sides are constrained by lateral supports). Finite element simulations are conducted to optimize the construction procedure. A comprehensive field monitoring program is implemented to the project, which is excavated using the optimal solution obtained from numerical analyses. Field measurements demonstrate that the top-down technique is effective in minimizing differential settlement and lateral displacement of columns and piles.