Top-down and bottom-up planning methods are two of the most popular approaches used in the construction industry. And building diaphragm walls is one of the most crucial stages of construction in building a deep basement structure using either top-down or bottom-up method.

Heritage Infraspace (India) Pvt Ltd (HIPL) is ranked as one of the best construction companies in India for its deep basement and underground construction services like diaphragm wall construction services in India for both top-down and bottom-up construction methods. Here, we brief you about how construction of the diaphragm wall in dams, metro stations, basement parking, etc. works, on both top-down and bottom-up construction.

What is top down and bottom up construction?

What is top down and bottom up construction?
Image Source – Researchgate

Tall buildings with deep basements and underground constructions like parking lots, underpasses, and subway stations are the two principal types of urban structures for which the top-down technique is applied. The technique has been applied to deep excavation projects where soil movements needed to be kept to a minimum but tieback or anchor installation was not an option. In this way, it is often possible to shorten the entire building period.

Buildings with underground basements are typically created using the bottom-up approach, where substructure and superstructure floors are built one after the other, starting at the lowest level of the basement and working their way up. 

Although this traditional approach, often known as the bottom-up approach, is straightforward in both design and construction, it is not practical for large-scale projects with constrained construction time or site conditions.

Diaphragm construction in both bottom up and top down construction

Diaphragm walls help form the perimeter walls of the excavation site and push the surrounding soil back, preventing the excavation site from collapsing. A hydro fraise machine is typically used for diaphragm walls. A special blade attached to the boom arm of this machine allows a bentonite slurry to be pumped down to the cutters, preventing the excavated area for the wall from collapsing.

The cutter descends to the desired level, and the slurry mixture aids in the preservation of the shaft. Rebar cages are then lowered into the shaft to provide reinforcement for the being built wall.

While one wall is being finished by pouring concrete and pumping out the bentonite slurry, the process on the opposite side begins. Depending on the soil quality, it is sometimes possible to build diaphragm walls on both sides at the same time. HIPL has, in the past, achieved this feat, making it one of the trusted construction companies in India. Rebar is lowered into the completed shaft for wall reinforcement once more. Once all of the walls are completed, the excavation site will have a rigid vertical structure to keep the surrounding soil from moving and collapsing into the excavation area.

When providing diaphragm wall construction services in India, once the excavation begins, posts or piles are driven into the ground to act as pillar supports for the earth retaining system. The struts are then installed as the next component of the earth retaining system. These are the horizontal braces that push the diaphragm walls apart and prevent them from inward movement.

Struts are installed at regular intervals to keep the diaphragm walls apart as the excavation progresses downward. The base slab is cast once the desired level is reached. In top down construction, the roof slab is cast before excavation begins. Access shafts in the roof slab are constructed to allow for the delivery of machinery and materials below for further excavation of the lower floors.

top-down and bottom-up construction
Image source – YouTube – Pooja Hegaje

The intermediate level slabs are now cast, and struts removed as the structure takes shape. As the structure takes over the function of the struts in holding the walls apart, the struts can be removed as the structure rises.

The slab casting continues upwards in the bottom up construction, as does the strut removal. Once the roof slab is cast, preparations for the construction of entry points begin with the removal of the final layer of struts.

All struts are removed once the walls of the entry points are up and the roof slab is complete. Post this, the diaphragm wall construction gets completed and the next stage of construction of the basement continues.

The points of distinction

The top-down approach provides for minimum acquisition or demolition during development while allowing excavation to go on in heavily populated regions. Although switching back and forth between different procedures makes it slightly more difficult than the bottom-up approach, it enables the construction of stations in heavily populated locations.

Working in such areas is difficult due to the slabs being cast as the excavation progresses downwards, especially for a diaphragm wall used in dams. The availability of fresh air, as well as adequate lighting, is critical for the continuation of work. Crane access is not restricted up and down the sides of the excavation during bottom-up construction. This method is faster than the top-down approach for sites large enough to have a perimeter area to accommodate construction equipment and when the excavation is not wide.

But, a major point of advantage for top down construction is that it requires little or no temporary steel shoring, as a result producing good cost savings. Further, it requires no formwork for floors or roof too, which means significant savings in cost and time.

HIPL has been providing crucial geotechnical solutions for large-scale residential and commercial construction, dam projects, metro and subway systems all over the country for over a decade now. To know more about our construction projects in India or to collaborate with us on your upcoming projects, get in touch with us today. Send us an email on info@heritageconstruction.in or call 079 26840355

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