Top Down Construction Method


To build underground basements conventional method known as a Bottom-up method is used. In this method, construction start from the bottom of the substructure or the lowest level of the basement to the top of the superstructure. This method is simple in design and construction but it is not feasible for the gigantic projects with limited construction time. So a new method was introduced which is known as a Top-Down method. This method is more feasible than the previous Bottom- Up method.

Top-Down Method

Top down Method

This is one of the new methods for deep-seated stabilization is the use of the Top-Down method of self-management. The methodology for the implementation of the top notch is provided in the BS Code: 8002: 1994 for Guardian structures and is an innovative implementation method that has been adopted since the early 90’s and has been in place since 2001 in various countries such as the United Kingdom, America, Finland, China, Russia, Vietnam, Singapore and Iran have been used based on the needs of the site.

In the top-down method, the construction of the structure is in the level below the ground with the excavation and excavation. It is also possible to carry the floor above ground level with the advance of the underground floors. Basically, the Top-Down method significantly eliminates the possibility of damages to neighboring structures that are sensitive to deformations and movement of soil. Due to the ongoing upward and downward implementation of the project, the speed of the project has increased significantly and will reduce resource use and pollution and lead to higher cost efficiency.

The Steps to implement the Top-Down is done in the following order:

  • Construction of the retaining wall.
  • Construction of piles. Place the steel columns where the piles are constructed.
  • The first stage of excavation.
  • The casting of floor slab for first basement level.
  • Begining of the construction of the superstructure.
  • The second stage of excavation.
  • The casting of the floor slab for the second basement level.
  • Repeat the same procedure till the desired depth is reached.
  • Construction of the foundation slab and ground beams, etc.

Construction of the superstructure goes on till it gets finished.

Construction of retaining wall

  • Installation of the retaining walls

Top down MethodInstallation of the retaining wall is done before the excavation starts.

  • Excavation and installation of steel strut

Top down MethodThe soil just below roof slab level of the underground structure is excavated. Then struts are installed to support the retaining walls, which in turn support the soil at the sides.

  • Construction of the underground structure

Top down Method

The roof slab is constructed, with excess openings provided on the slab so that the work can proceed downwards.

  • Construction of the underground structure

Top down MethodThe next level of the slab is constructed, and  this process is continued till the base slab is completed

  • Construction of the underground structure

Top down MethodThe side walls are constructed and the intermediate struts are removed. The access openings on the roof slab are then closed.

  • Backfilling and reinstatement

Top down MethodIn the final stage, the foundation of the structure is executed and the openings formed in the ceiling slab (for the transfer of soil) are closed and the structure of the basement is completed.

In constructing a top-notch structure, in addition to conventional structural controls, simultaneous geotechnical considerations should be included in the design and implementation process of the structure. To this end, the structure should be controlled and designed by a structural engineer and a geotechnical engineer. Failure to overlook some of the various factors in the control and design process that will later be imposed on construction will result in irreversible consequences. Therefore, using accurate control of correct modeling and simultaneous consideration of geotechnical and structural considerations, damage can be avoided.



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