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Where is the tallest skyscraper in the world?

Instead of building the world's tallest skyscraper, why can't we start building the world's deepest building?

  • Instead of building skyscrapers up, why can't we build them down? In cities, buildings could be built below the pipes and the subways while there would be some saved space above for other recreational and residential buildings. We could stop worrying about skyscrapers being targets of terrorism and weathered building materials. I am not an engineer, so therefore I'm looking for what everyone has to say about this (engineer/architect insight preferred but not necessary) on the benefits and problems this may have on society, the environment, life of a building, etc... I know seismic activity would be an obvious problem but there must be a solution to that by the time there would actually be an underground skyscraper/city.

  • Answer:

    The answer is we can build the deepest building, but mostly we don't want to. A few things to consider. In most locations of the world, the ground is composed of layers of sands, silts, clays and organic top soils. Below these layers, sits bedrock. The depth to bedrock can range from a few feet to hundreds of feet. In many locations it is well under 100 feet. For example. here is a graphic depth of bedrock of Minnesota, USA.. Bedrock, as the name suggests, is very hard rock material. This means that constructing a very deep building in most locations wouldn't be so much an exercise in digging as an exercise in tunneling/boring. Tunneling through bedrock can be done. Here is an image of the Chicago deep tunnel  (http://en.wikipedia.org/wiki/Tunnel_and_Reservoir_Plan): The issue is that creating this tunnel has taken many years and it has been quite expensive. It does however serve an important function, in helping the region drain water better. So this is a major challenge for a building going excessively deep. With skyscrapers, the deep foundation systems overcome this issue by drilling or hammering in a series of relatively small foundation piers (3ft or 1m in diameter or so). Drilling a 2 or 3 foot hole can be done with normal equipment, while drilling a ten, 50 or 100 foot diameter vertical hole would require an entirely new invention. As others have pointed out, there is a serious issue with supporting the soil's outward pressure; this can be resisted by constructing a slurry wall or sheet pile wall. Here is a sheet pile wall: But, there are limits to what this sort of wall can resist. The pressure increases linearly with the depth and eventually the wall would become extremely difficult to construct. If we try to cast a concrete/grout wall to resist the pressure, the construction process is very problematic. If we managed to dig a several hundred foot vertical shaft and the soil was feeling generous, not collapsing inward and waiting for us to build the wall, the challenge of casting this concrete would still be great. We would have to deal with ground water issues, which will tend to fill the hole and destroy the concrete mix, and we'd have to deal with the vertical and horizontal pressure of the concrete. Until the concrete sets up into a solid, it functions like a liquid and instead of being a load resisting element, it is a load producing element! Here is the closest example I can think of for this sort of thing. This is an image of the foundation of the never completed http://en.wikipedia.org/wiki/Chicago_Spire. It has a 104 foot diameter is 74 feet deep. If a structure were built inside, it would be 6 or 7 stories tall, by no means a skyscraper. As the depth increases further, the sheet pile wall (the vertical brown members in the image) would need to stronger and stronger (heavier) Now, we could combat these issues by digging the hole much wider, to the http://en.wikipedia.org/wiki/Angle_of_repose, at which point the soil will naturally remain stable without the need for a resisting wall. We could then build our structure inside this hole, and then back-fill the soil afterwards. However the construction of this structure would now proceed like the construction of a skyscraper, it would just happen to be a skyscraper placed inside of a big hole. In its completed form, the skyscraper would still need to resist the later soil pressure, which means the walls and framing would be massive. Essentially what we would be doing is building a skyscraper at the bottom of this: And then filling it back in afterwards. This would be unbelievably expensive and time-consuming. And after all the effort and expense, we'd be left with a building that I believe the vast majority of people would find quite undesirable.

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Money. There's no compelling reason to build super-deep for office space--the primary function of a skyscraper. Sure, there's plenty of "space to develop" down below grade but the costs of going very deep are prohibitive. The lateral earth pressure forces are quite large--and water is an even bigger issue...These aren't things geotech engineers can't overcome but the costs are enormous. There are deep military installations, missile silos, and mining works which go down quite deep. There are some mines many times deeper than the Burj Khalifa is tall--but the miners who spend an hour or more getting to the bottom of a mineshaft to work the face every day aren't getting any natural light or ventilation. The owner of an upside-down sky-scraper would be hardpressed to sell prestigious firms looking to rent space moldy penthouse suites hundred of feet below grade with no views, no sunlight or windows and no natural air. Also in areas where development is dense enough for skyscrapers (major urban cores) there is typically a poorly documented 3 dimensional labyrinth of utilities and/or subway infrastructure that would be extremely expensive and possibly dangerous (at least from a liability POV) to build into. It's simply cheaper, more gratifying for the architect and owner, and more satisfying for the building occupants to be up above ground.

Matthew Sutton

seismic forces, and the fact that it gets hotter as you go deep enough and increases costs of air circulation cooling. Much of the energy you get above the ground, , incl. light won't be available below

Venki Nishtala

Problems of ventilation, cost of constructing retaining walls supporting soil mass of higher than 13 m in depth is very high , pumped drainage is required to pump the waste water up to the sewer pipes.

Shivam Mathur

Building Deep (inwards) = Digging + Building a skyscraper in the hole (upto ground level) Going by common sense, and for better efficiency and productivity, I would avoid the digging part (process intensive, and many time more complex than building the skyscraper) and just build the skyscraper. Therefore people build skyscrapers. Q.E.D.

Amit Saxena

There are two main reasons that I wouldn't build deeper instead of taller;1. Light 2. Pressure1. Building vertically allows for natural light to penetrate to the interior of a building. Believe it or not this is crucial to the usability of a building. Natural light is affects human comfort and regulates natural sleep cycles. Creating artificial light to replace natural light is not only more expensive over the lifetime of a building but it doesn't do the job. Artificial light as it exists today normally provides light of a narrow wavelength range. 2. Building deeper instead of taller requires enormous structural reinforcement to shore up walls. In vertical buildings we fight gravity, seismic loads, wind loads, and static & dead loads. In subterranean buildings we fight all of these (except for wind loads) but now we have to deal with lateral pressure from soil, rock and hyrostatic pressure (or the pressure of subsoil water pushing against subterranean walls). These loads are tremendous and only increase with depth. Therefore a deep vertical building would consume enormous amounts of material to keep from implosion and be illuminated with mostly artificial light.

Jacob Douenias

I believe that many people will praise the architect for the amazing skyscraper facade, building envelope and shape of the building. Can you imagine if the trend change to underground skyscraper ? I think the architect won't be the "hero" anymore for the building, cause the engineers will take the credit for giving the best structure and good building system.

Willy Yu

As we go deeper into the earth, the temperature and pressure increases because of having more matter around that empty space. And maintaining these conditions of increased temperature and pressure is costlier than maintaining the same conditions above the earth.

Naren Immadi

Your question reminds me of a sci-fi movie I had seen as a child. It showed Earth and its people in 3000 AD. Ozone layer (up above in the Stratosphere) is completely wiped out due to high levels of pollution and Chloro Fluoro Carbons (CFCs). Rampant deforestation resulted in no tree cover on the planet and the temperature rose to beyond tolerant levels. People, dressed up in space-suit like attire to protect themselves from the external conditions, started living underground. Man had become technically very advanced and everything from communication towers to submarines and buildings were built underground.  Thus, underground cities developed and the entire life moved to sub-ground level to adapt to the changing environment! Now, back to reality, as long as all is well above planet Earth, I don't think underground cities (or habitable buildings) will even be a remote possibility. Most living organisms love light and sun, something that can never be naturally found underground.

Yashaswini Subraveti

If you are to ask any Civil /Geotechnical Engineer / construction manager what cost is the most expensive in terms of erecting a building. The answer would be the ground works...simply the displacement of underground water through lowering the watertable (which can have detrimental effects to other localised buildings if not fully considered) but there is also the high risk to contaminate ground water. As there is alot of hydro-static forces to contend with,exstensive structural calculations would be required to offset any seismic or increase in ground water levels in the future. In creating multi-story underground buildings the dewatering of the local water table will have knock on effects to local ecology and habitat especially if located near a water body. In other words the further you develop into the ground the higher the upfront cost values (ecological and habitat destruction, unnecessary alteration to sub-surface water streams etc) for construction are. I believe these are the main reasons for not building underground sky scrapers (along with sunlight deprivation)!

Vincent Byrne

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