Why do the foundations of skyscrapers take several years to build?

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Underground work in ordinary high-rise buildings is completed in four months, but for a high-rise building it takes a year and a half

Moscow is moving higher and higher. Today in the capital, according to the Metrium company, 60 residential complexes with skyscrapers – buildings higher than 100 meters – are already being built. The height of such buildings reaches 85 floors or 340 meters. Such projects often implement the concept of a “vertical city,” which includes placing the infrastructure of entire districts – social facilities and jobs – in close proximity to housing. However, such complexes can take longer to build, and raising the foundation higher can take several years. Experts from the Elitnoe.ru portal learned from representatives of real estate agencies how long it takes to build the foundation of an ordinary house and a skyscraper, and also what is the difference between such work.

Director of the residential real estate sales department of the Summa Elements Group of Companies Svetlana Bardina:

– In a mid-rise apartment building, excavation work lasts from 14 to 45 days. During this period, the developer carries out basic activities to form a pit, lays trenches for supplying communications, and installs piles. Subsequent foundation work lasts from 1.5 to 3 months. If construction begins in the cold season, then this stage lasts longer. In total, zero-cycle work in the case of a standard high-rise building takes approximately 1/10 of its construction time.

The situation is different with skyscrapers. The absence of visible external changes at the construction site at the beginning of the implementation of a high-rise project is an absolutely normal situation due to objective reasons. To make high-rise buildings stable, a very deep pit is required: on average 20-25 meters versus 4-6 meters in other cases. Specific indicators depend on the mass of the future building, the bearing capacity of the soil, the hydrological regime, etc. To make a high-rise building under construction truly durable and safe, it is necessary to prepare the site, install fences and install a spacer system to hold them, remove the soil, build pile foundations, create foundation slab and frame bases. All this usually takes from a year to a year and a half, that is, a third of the entire period of construction of a skyscraper.

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Owner of luxury real estate agency Nika Estate Viktor Sadygov:

– The construction of high-rise buildings is associated with many problems. But if the safety of the above-ground part of buildings is related to the quality of materials and the human factor, then their underground part is exposed to a much greater number of risks. The most powerful terabyte computer is not capable of calculating and anticipating them all. Therefore, designing the foundations of high-rise buildings is perhaps the most difficult and crucial moment in the construction process. The entire future fate of the skyscraper and the buildings located in the neighborhood depends on the successful completion of the initial stage of work.

Naturally, the higher the building, the more it puts pressure on the base of the foundation. The total vertical load can reach astronomical values. Not every soil can withstand the pressure of a multi-story building. Engineering-geological surveys are one of the most important activities when preparing a project for the construction of high-rise buildings. The development site is subjected to ultrasonic scanning, and wells up to 100 meters deep are drilled into the ground. Soil samples are taken at different elevations to determine their composition. There is a risk of unexpectedly stumbling upon underground water, sinkholes, caves; the soil itself may have a small margin of safety.

In Moscow, piles are most often used in the construction of high-rise buildings. But if, with a building height of up to 20 floors, the designer has a choice of whether to use piles or not, then when constructing high-rise buildings they are mandatory. The depth of these piles can be 50 meters, the diameter is one and a half. The cost of a linear meter of a pile with a diameter of 1 meter is about 40 thousand rubles. The thickness of the foundation slab can reach four meters. In each individual case, the type of pile may vary. Installation is carried out using different technologies: you can drill, fill with concrete, lower a core inside – a special type with which the piles can withstand up to 30-40% more load. The walls of the pit are reinforced along the perimeter with reinforced concrete.

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Given the uniqueness of high-rise buildings of the first category of responsibility and the imperfection of the existing regulatory framework, during the construction of high-rise buildings it is recommended to constantly monitor the condition of the soil, piles, grillage and enclosing concrete structures. If we take the average time for the construction of skyscrapers, then about 20-30% of the time will be spent working on the foundation pit. They depend on weather conditions, the design of the house, and the chosen technology.

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