Structural behavior in top-down excavation method

The top-down excavation technique is one of the alternative methods to effectively reduce the completion time of construction projects. In this study, the structural behavior of three casting stages of strut ring slab is assessed using finite element simulation. The stages are introduced to analyze various excavation steps before the completion of slab construction. Hence, the probability of excavation initiation can be investigated. The results indicate that whenever the slab is casted for one strip and excavation is subsequently commenced underneath, the moment value, steel requirement, slab stress, and support reaction are generally lower than the case when digging operation is started after the casting of the full ring. By contrast, if two thirds of the slab is constructed and excavation begins underneath, the moment value, deflection, stress, and support reactions are quite higher than those of a fully casted slab.