Top-down construction is the opposite of bottom-up construction. The permanent structure is erect from the top to the bottom of the basement. With deep excavations between. The basement floors build as the excavation continues in this technique. The concrete slabs brace the perimeter wall system in the basement. It pours ground level and basement slabs with access holes.
When finish, the floors operate as lateral bracing for the perimeter wall system. The perimeter wall is a single, safe solution to all the construction issues. Diaphragm walls are useful for retaining the earth and controlling groundwater movement. It is capable of carrying superstructure loads. Allowing for early use of the superstructure even before the building’s substructure completes.
The top-down method is being used by Construction Companies in Calgary or elsewhere for deep drilling projects. Some examples are subway station construction, tunnel construction, underground mining, etc.
Procedures for Top Down Construction
Use in urban infrastructure projects is Top-down building construction. Such as underground parking, underpasses, even subway stations. Also, skyscrapers, and steel buildings in Alberta and other places.
The techniques outlined below are more generic in nature. They will vary depending on the project.
Using the diaphragm walls
Diaphragm walls are first drilled and cast their foundations. Also known as cutoff walls. They can be sheet piles, pipe piles, or soldier piles. Also, diagram walls, depending on the conditions on the job site. Different factors determine the thickness of the wall and the distance between panels. These can be the kind of soil and the quantity of surcharge that must sustain. In most cases, 24″ to 48″ is enough for typical conditions. Although the wall should embed in the soil at full depth.
Drilling the piles
Depending on the site situation, piles should drill using auger boring. Or percussion boring to transfer the load of the building to the hard-bearing stratum. Steel stanchion columns should embed below.
Using the steel columns
Steel columns will support the superstructure’s load. And they must be strong enough to withstand the imposed load during construction. The bottom floor base slab is thicker than the rest of the slabs. And it serves as lateral support for the columns and diaphragms walls.
Working around ground floor slabs
The space within diaphragm walls is then excavated to the ground floor slab level. The ground floor slab is then concreted. And the diaphragm walls should reinforce with steel. Rebars with end couplers are usually left at the floor slab level during casting diaphragm walls. Which are later connected with the reinforcement of the ground floor slab. The slabs have to get entry to voids at appropriate distances. The excavation must sustain downwards for the second degree of excavation. And then on the primary basement ground degree.
Metallic stanchion columns
The metallic stanchion columns should bolster via reinforcing bars. After reaching the intensity of 1 stage of the basement. These will serve as everlasting columns for the basement floor. The diaphragm partitions are also supported with accelerated thickness to grow a lasting part of the structure.
The operation repeats floor by floor of the basement to reach the needed number of basement floors. The access slots left for excavation in the slabs cover up with reinforced concrete slabs that match the floor slab.
Benefits Of Top-Down Construction
Reduced construction time
The structures above ground can restore at the same time as the structures below ground. Construction time for construction companies in Calgary and other areas is shorter due to this.
Concrete diaphragm partitions are extra cost-effective. At the same time, they can feature as a groundwater cutoff. And a brief soil retention device in the excavation section of the project. These partitions can work as permanent underground partitions. With load-sporting abilities for the completed structure.
Roofs come handy
Roofs are easier and more cost-effective to construct. Because they may be cast on prepared grades rather than bottom forms.
Some other benefits are:
- The structural slab acts as an inner bracing for the guide of excavation. Decreasing the variety of tiebacks required.
- The almost vibration-free operation reduces the risk of ground movement. And the resultant unfavorable settlement.
- It necessitates a smaller construction space. Pre-construction earthworks help to lessen environmental pollution.
- It is no longer necessary to underpin adjacent constructions.
To wrap up, the top-down style of construction reduces the construction time in a construction company in Calgary or any other city. As a result, large excavating projects in Calgary or elsewhere use this when time is a critical element.