<p>This question is not about earth science. If anything, it has more to do with engineering.</p>
<p>Strategic or critical defense or government infrastructure needs to be protected against explosive attacks, particularly nuclear attacks. A mountain offers a sizeable protective cap/roof to an underground installation. Similar levels of protection can be provided in flat ground, but the underground installation would need to be significantly deeper.</p>
<p>Critical parts of the installation would not be established within the mountain above the level of the ground surrounding the mountain; it would be established below.</p>
<p>Additionally, many mountains are composed on igneous rock: rock that solidified from a molten mass. Such rock, such as basalt or dolerite (diabase), is typically stronger than sedimentary rock and can thus offer better blast protection than sedimentary rock.</p>
<p>Also, if the installation is established igneous rock, the same strength parameters can also mean reduced geotechnical and subsequent ground support measures would be required for the underground voids that if they were established in sedimentary rock.</p>
<p><a href="https://www.popularmechanics.com/military/a32380097/norad-cheyenne-mountain-fortress/" rel="nofollow noreferrer">Cheyanne Mountain</a> is composed of granite, and igneous rock that solidified while still underground. The NORAD installation within Cheyanne Mountain &quot;was designed to ride out a nuclear attack&quot;. Having been completed in 1966, when tunnel boring machines were not a consideration, it was established using drill and blast methods and consumed <a href="https://en.wikipedia.org/wiki/Cheyenne_Mountain#NORAD_operations_center" rel="nofollow noreferrer">500 tons of explosives</a>.</p>

CC BY-SA 4.0
2023-12-20T07:37:29.920Z
Would such mountain bunkers require concrete rebars or ultra high performance concrete (UHPC) to supplement the igneous rock of the mountain?
dazzleworth
CC BY-SA 4.0
2023-12-20T08:11:26.310Z
@dazzleworth: that would depend on the geological and geotechnical conditions for each site, the ground reinforcing/support technology that was available at the time of establishment, the ultimate purpose of the facility & the duration that it needed to be operational. A facility such as NORAD's operation at Cheyanne Mountain these days would used cable bolts, rock bolts & ultra high performance concrete for its survivability during a potential attack, but also to ensure loose rocks don't fall off the walls & ceiling damaging internal infrastructure or injuring personnel.
Fred
CC BY-SA 4.0
2023-12-19T00:42:41.030Z
2023-12-19T00:55:01.427Z
2023-12-19T00:55:01.427Z
Fred
<p>It is possible, but three reasons at least play in favours of remote mountain locations:</p>
<ul>
<li><p>It is easier to dig into mountains, because you can start with the excavation directly from the mountain side, instead of having a vertical huge shaft that brings your equipment at depth into the rock formation of interest: it is easier to excavate tunnel horizontally than large diameter shaft vertically (easier, not easy :) );</p>
</li>
<li><p>It is easier to control access and safety of a remote installation, rather than an installation build in the middle of an urban environment;</p>
</li>
<li><p>the structure in the mountain allows for easier control of water infiltrations and air circulation.</p>
</li>
</ul>

CC BY-SA 4.0
2023-12-18T23:41:49.130Z
Tunnel boring machines are not required to make tunnels. They might be in vogue now, but [drill & blast](https://drillitco.com.au/what-is-the-drill-and-blast-tunneling-method/) techniques were used in the past. Secondly, shafts would not be used to provide initial access for tunnel boring machines. If there isn't a hill to bore into they start at the surface using a [box cut](https://www.greatmining.com/box-cut.html) in the surface. Your second point is also incorrect; plenty of rail & road tunnels have been established in urban areas, with & without tunnel boring machines. ...
Fred
CC BY-SA 4.0
2023-12-18T23:46:29.983Z
... Your third point is also incorrect, particularly concerning air circulation. Fan forced ventilation will be used to get the air flow rates required. As for water infiltration, you comment may be applicable if the underground opening are above the land surface of the surrounding countryside. If they go below, there is no advantage.
Fred
CC BY-SA 4.0
2023-12-19T10:19:46.273Z
@Fred Thanks for your comments! The second point applies obviously to the (future) structure itself, not to the excavation operations. The third point your correction is wrong. It is much easier to take care of water with drainage from the mountain: all you need is water collection and a bit of slope towards the exit. If you are underground, you need to actively pump it out or to set up higher pressure in the tunnel, which is more complex. Considering drill and blast, it is still easier and quicker to carry material horizontally than vertically. And CMC building is very obsolete.
EarlGrey
CC BY-SA 4.0
2023-12-18T10:20:51.343Z
2023-12-19T13:17:55.387Z
2023-12-19T13:17:55.387Z
EarlGrey
<p>Why is it that underground facilities (or underground military bases) are almost always built into hollowed out mountains? Examples of (publicly known ones anyway) are Cheyenne Mountain Complex and Mount Weather government/ military facilities. Is having a highland/mountain a prerequisite for construction of military/government facilities? Is is not possible to construct facilities beneath lower ground, plains, dessert or under cities, besides subway stations and tunnels? Say if we wanted to build NORAD bunker somewhere deep beneath San Jose population centers, is this possible discounting the fault lines and permits for now?</p>

<earthquakes><soil-science><bedrock>
Question regarding underground man-made facilities
dazzleworth
# Question regarding underground man-made facilities

(Asked by: username_0 on 2023-12-18)

Why is it that underground facilities (or underground military bases) are almost always built into hollowed out mountains? Examples of (publicly known ones anyway) are Cheyenne Mountain Complex and Mount Weather government/ military facilities. Is having a highland/mountain a prerequisite for construction of military/government facilities? Is is not possible to construct facilities beneath lower ground, plains, dessert or under cities, besides subway stations and tunnels? Say if we wanted to build NORAD bunker somewhere deep beneath San Jose population centers, is this possible discounting the fault lines and permits for now?

**Tags:** earthquakes, soil-science, bedrock


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## 2 answers

### Answer by username_1 on 2023-12-19. Score: 1 | Accepted answer

This question is not about earth science. If anything, it has more to do with engineering.

Strategic or critical defense or government infrastructure needs to be protected against explosive attacks, particularly nuclear attacks. A mountain offers a sizeable protective cap/roof to an underground installation. Similar levels of protection can be provided in flat ground, but the underground installation would need to be significantly deeper.

Critical parts of the installation would not be established within the mountain above the level of the ground surrounding the mountain; it would be established below.

Additionally, many mountains are composed on igneous rock: rock that solidified from a molten mass. Such rock, such as basalt or dolerite (diabase), is typically stronger than sedimentary rock and can thus offer better blast protection than sedimentary rock.

Also, if the installation is established igneous rock, the same strength parameters can also mean reduced geotechnical and subsequent ground support measures would be required for the underground voids that if they were established in sedimentary rock.

[Cheyanne Mountain](https://www.popularmechanics.com/military/a32380097/norad-cheyenne-mountain-fortress/) is composed of granite, and igneous rock that solidified while still underground. The NORAD installation within Cheyanne Mountain "was designed to ride out a nuclear attack". Having been completed in 1966, when tunnel boring machines were not a consideration, it was established using drill and blast methods and consumed [500 tons of explosives](https://en.wikipedia.org/wiki/Cheyenne_Mountain#NORAD_operations_center).

> **Comments:**
> **username_0**: Would such mountain bunkers require concrete rebars or ultra high performance concrete (UHPC) to supplement the igneous rock of the mountain?  
> **username_1**: @username_0: that would depend on the geological and geotechnical conditions for each site, the ground reinforcing/support technology that was available at the time of establishment, the ultimate purpose of the facility & the duration that it needed to be operational. A facility such as NORAD's operation at Cheyanne Mountain these days would used cable bolts, rock bolts & ultra high performance concrete for its survivability during a potential attack, but also to ensure loose rocks don't fall off the walls & ceiling damaging internal infrastructure or injuring personnel.  

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### Answer by username_2 on 2023-12-18. Score: 1

It is possible, but three reasons at least play in favours of remote mountain locations:

* It is easier to dig into mountains, because you can start with the excavation directly from the mountain side, instead of having a vertical huge shaft that brings your equipment at depth into the rock formation of interest: it is easier to excavate tunnel horizontally than large diameter shaft vertically (easier, not easy :) );
* It is easier to control access and safety of a remote installation, rather than an installation build in the middle of an urban environment;
* the structure in the mountain allows for easier control of water infiltrations and air circulation.

> **Comments:**
> **username_1**: Tunnel boring machines are not required to make tunnels. They might be in vogue now, but [drill & blast](https://drillitco.com.au/what-is-the-drill-and-blast-tunneling-method/) techniques were used in the past. Secondly, shafts would not be used to provide initial access for tunnel boring machines. If there isn't a hill to bore into they start at the surface using a [box cut](https://www.greatmining.com/box-cut.html) in the surface. Your second point is also incorrect; plenty of rail & road tunnels have been established in urban areas, with & without tunnel boring machines. ...  
> **username_1**: ... Your third point is also incorrect, particularly concerning air circulation. Fan forced ventilation will be used to get the air flow rates required. As for water infiltration, you comment may be applicable if the underground opening are above the land surface of the surrounding countryside. If they go below, there is no advantage.  
> **username_2**: @username_1 Thanks for your comments! The second point applies obviously to the (future) structure itself, not to the excavation operations. The third point your correction is wrong. It is much easier to take care of water with drainage from the mountain: all you need is water collection and a bit of slope towards the exit. If you are underground, you need to actively pump it out or to set up higher pressure in the tunnel, which is more complex. Considering drill and blast, it is still easier and quicker to carry material horizontally than vertically. And CMC building is very obsolete.  

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