Engineering and Construction

Normally, the substructure of a building is completed before work begins on its superstructure. If the building  has several levels of basements, however, substructure work can take many months or even years.

In such a case,  up–down construction is sometimes an economical option, even if its first  cost is somewhat more than that of  the normal procedure, because it can  save considerable construction time.

As diagrammed in Figure 2.69,  up–down construction begins with  installation of a perimeter slurry  wall.

Internal steel columns for the  substructure are lowered into drilled, slurry-filled holes, and concrete footings are tremied beneath them. After  the ground floor slab is in place and  connected to the substructure columns, erection of the superstructure may begin. Construction continues  simultaneously on the substructure, largely by means of mining machinery: A story of soil is excavated from  beneath the ground floor slab and a  level mud slab of CLSM is poured.

Working on the mud slab, workers reinforce and pour a concrete structural slab for the floor of the topmost
basement level and connect this floor to the columns. When the slab is sufficiently strong, another story of soil is removed from beneath it, along with the mud slab. The process  is repeated until the substructure iscomplete, by which time the super-structure has been built many storiesinto the air.

Figure 2.69 Up–down construction.