The congested conditions of metropolis historic centres and complicated geological and hydro-geological conditions during the construction of new building zero cycles and underground car parkings force to apply semi-closed method as the most safe for the surrounding built-up area.
In that case the ground excavation in a pit is performed under the protection of floor-slabs that are erected according to the «top-down» method and are supported with intermediate temporary steel props or permanent reinforced concrete ones.
Due to the complexity of vertical position ensuring, reliable coupling with the floor-slabs and required bearing capacity during exploitation, these props, as a rule, are made as temporary steel props reinforced by reinforcement bars and concrete solidification during the construction completion phase.
Mach more rarely the permanent props are used that are erected in the bored holes or short trenches using precast concrete elements joined during the assembly. Complicated execution of reliable butt-joints of elements and units connection with the underground storeys floor-slabs as well as additional expenditure due to manufacture and transportation are hardly attractive.
The subject of the article is a detailed consideration of a fundamentally new technology for the erection of bored columns
made of in-situ reinforced concrete and of high execution accuracy and bearing capacity. The author especially introduces the term «bored columns
» into practice to point out distinctions of applied for the first time in the world decision from the well-known bored piles or precast reinforced concrete columns erected in the bored holes.