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We shared Mechanics of materials with structural engineers back in college. I learned some basic concept about structural engineering, but besides the basic knowledge i don't know anything about structural engineering.

If i recall correctly, an engineer found a way to distribute the weight of buildings over a wide area to reduce the stress, i think he managed to solve the problem of sinking buildings for the first time in Chicago, and up to this moment, his solution has been popular.

If the area has a strong bedrock, manhattan for instance then, the buildings are much more stable, but my question targets the areas with very weak bedrock, The Hague for instance.

I can say, there is channel is every street, when i walk in streets i can actually hear the vibrations of water beneath my feet, if you dig the ground four or five meters, in city centre you'll reach water.

I wonder how engineers manage to build skyscrapers in this area? The concentration of tall buildings is not as same as in manhattan, Chicago or ... . But still, how those few tall buildings are still on the ground?

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As part of the process of obtaining a building permit is the requirement to investigate the soil strength and competency and possible elevated subterranean water levels by a licensed geotechnical engineer and if needed in some cases by a multitude of engineering specialists' investigation, such as geology, seismology, and any other concerns pertinent to that site investigation as determined by the building department authority.

Geotechnical engineers, after studying the site and tabulating logs of test pits and doing lab test on the excavated samples, submit a report with specific recommendations for construction of that particular building on that site including modifications to the soil by additional foreign materials, borehole drainage among other things.

The structural engineer following geotechnical recommendations and using their approved tables of such things as allowable bearing, shear strength, passive and active soil pressure, seismic and dynamic over loads, and if there is need of use of mat foundation or deep foundation supported on piles or need of subterranean drainage (boreholes) to drain moisture of soil to acceptable level, design the building closely following the geotechnical engineer's report. Then the structural engineers send their design to geotechnical engineer and if he approves it they submit it to the building authority to get the permits.

In cases of weak soil or subterranean water, in some cases they recommend building a big subterranean concrete cube a little bigger than the entire subterranean parking and foundation of the building, like a giant dry swimming pool and water proof it and install emergency sump pumps or alternative means of drainage, then they start to build the foundation inside that giant concrete clad excavation. This is similar to the way bridges are built in rivers.

In some other soft incompetent soils the geotechnical engineers may recommend building a system of deep piles tied and integrated with each other, called soldier piles, and then build the building on top of it.

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  • $\begingroup$ Great, i think this is the answer, but do the emergency pumps remain functional after construction? In designing the wind turbins in the same city, we have to redirect a portion of generated electricity to those pumps to drain the foundation, pumps always work 24/7. $\endgroup$ Nov 16 '18 at 21:15
  • $\begingroup$ @Sam Farjamirad, yes and they have to have their own independent emergency power generator. In many coastal cities such as. Vancouver in Canada or Seattle in Us it's the code. $\endgroup$
    – kamran
    Nov 16 '18 at 21:50
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You don't need any modern technology to succeed. The tower of the tallest medieval building in Britain, the main church in Boston, was completed in 1520. It is 83m (280 feet) tall, and built on ground which is almost pure silt, and only 10 meters away from a tidal river.

Because of the difficult soil conditions, digging the deep foundations was "sub-contracted" to coal miners from a different part of the country. The building has never needed any structural reinforcements in the 500 years it has been standing, and the top of the tower is only 5mm away from being perfectly vertical.

https://en.wikipedia.org/wiki/St_Botolph%27s_Church,_Boston#/media/File:St_Botolph%27s_Boston_ext.jpg

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Usually using piles in multiple vertical arrays is the answer. The friction between the soil and rock against a long vertical concrete column can be substantial enough to provide more than enough reaction force to the compressive load applied by structures on it. A good example is the Shard in London which was built this way. The clay soils in London are notoriously unstable and the 97 floor tower rests on these piles. Shard construction Impossible Engineering Documentary

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  • $\begingroup$ The second video around 5:55 shows the 23 piles that the Shard is built on $\endgroup$
    – Rhodie
    Nov 23 '18 at 1:28

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