Top-down method is mostly suitable for two types of urban structures, tall buildings containing deep basements and underground structures like car parks, underpasses and subway stations. In such a circumstance the basement floors are built up as the excavation steps forward.
The top/down method is utilized for deep excavation projects where tieback installation can’t be done and soil movements should be reduced. Top-down construction method saves the entire construction time. So, it is mainly implemented for some major projects where time is a key factor.
The sequence construction starts with retaining wall set up and then load-bearing elements to support the future super-structure. The basement columns (generally steel beams) are built up prior to starting of excavation and rest on the load bearing elements. These load bearing elements normally belong to concrete barrettes constructed under slurry (or caissons).
Construction method: Given below, the detail construction method for top down construction :-