Details of top down construction method

Under top down construction method, the basement concrete slabs function as lateral bracing toward the perimeter wall system. Ground level and first basement slabs are poured, with access holes left to facilitate excavation below. Since every succeeding sub-grade level is finished, the floors perform as lateral bracing toward the perimeter wall system.

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 :-

• Built up the retaining wall.
• Build up piles. Arrange the steel columns or stanchions where the piles will be developed.
• Carry on the first phase of excavation.
• Cast the floor slab of first basement level
• Start to build up the superstructure
• Carry on the second phase of excavation; cast the floor slab of the second basement level.
• Reiterate the similar method unless the required depth is attained.
• Develop the foundation slab and ground beams, etc. Finish the basement work.
• Continue constructing the superstructure unless it is completed.

To learn the step-by-step process in detail, go through the following video presentation.

Video Source: geobuuk

Details of top down construction method