How does the temperature vary throughout a tunnel? 2

[bojoka4052]

For example it tends to be colder at the opening, but warmer as we move further in? It would also make sense that the temperature only goes up a little during the summer, and a bit down during the winter months deeper inside the tunnel, compared to right by the opening; where I imagine the temperature would go up and down much more?

Edit: I ask because of joint sealant for concrete, I get too much displacement in the concrete due to rise and decrease in temperature. I am thinking this cannot be realistic numbers (5 mm) deep inside the tunnel. Maybe in reality the temperature is significantly lower.

 

[SlideRuleEra]

bojoka4052 - This is really a (conduction) heat transfer problem. The earth has a molten core that is semi-infinite in size (for practical purposes). Go deeper underground, soil temperature gets hotter. The first 10 meters, or so, of depth are affected by sun and surface temperature. As depth increases from 0 to 10 meters, varying surface condition have a steadily decreasing effect. At a given depth below 10 meters, soil temperature is essentially constant.

http://www.SlideRuleEra.net

 

[miningman]

Bojoka, I have to ask , is your concern in an existing tunnel or is it generated by a computer model??? If its a computer model , GIGO. In reality in a real tunnel , the surrounding rock acts as an infinite heat sink. And yes , conditions at the tunnnel mouth will not represent conditions say 200 metres from the mouth. I have never experienced conditions within a tunnel that gave rise to tunnel stability concerns and I have worked in literally miles of underground workings.

 

[bojoka4052]

Its an existing underground tunnel, I am trying to figure out the temperature inside the tunnel. The tunnel has been designed as if it were an outdoor structure in the shade all throughout the tunnel, which I feel must be quite far off. Especially as we get further in the tunnel. I am thinking as the hot summer air enters during summertime, it will be cooled off as it travels further in due to the surrounding rock, and the opposite during winter, the air will get warmed up as we move further in. But its very hard for me to say how much this will change the temperature. Say it has been designed for +30C and -30C outdoor air temperature; how much could one expect the temperature to change 100m in? 1000m in? - and how could I justify explaining this without any calculations to show for it.


Ive been told there is ventilation in the middle of the tunnel, and it pumps out dirty hot air but pumps in cold clean air, also that it most likely wont be cold here which I struggle to understand why.

 

[WARose]

I would think once you get the worst case air circulation (in terms of temperature) tied down you could then tie down what it is. (Since we are talking a conduction/convection issue.)

Just a guess: most probably the heat loss from contact with the soil would outweigh the increase from the air flow. But without hard numbers (i.e. fully defining the problem)....it is difficult to say.

 

[bojoka4052]

Thats the problem, I cannot get hard numbers, just need the best educated guess with the limited information I have

 

[MotorCity]

If this is an existing tunnel and you want hard numbers, use a thermometer.

 

[miningman]

Well IMO , at 1000 metres from the portal , the air temperature has definitely stabilised to reach the virgin rock temperature. It probably reaches equilibrium at 400- 500 metres from the portal. There is probably geothermal information on line for your geographical location to provide initial estimates. If this is Norway, conditions are probably similiar to Canada but even within Canada there are large local variations..... permafrost being one extreme. But then one has consider other sources of heat.... diesel motors running , water flow , ventilation quantities. This is starting be be a "how long is a piece of string??? " debate

 

[IRstuff]

https://www.scientificamerican.com/article/the-temperature-of-the-earths-inter/

https://www.tandfonline.com/doi/abs/10.1080/01430750.2000.9675374

https://www.architectmagazine.com/t...f the Earth,wider adoption of the technology.

So not only is it stabilizing to the temperature of the rock; its temperature is relatively stable. What the actual value is will vary:

https://www.weather365.net/en/weath...e/norway/step-2/surface/soil-temperature.html

https://www.cbc.ca/news/science/norway-s-ark-underground-vault-to-house-world-s-seeds-1.748890

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[WARose]

Thats the problem, I cannot get hard numbers, just need the best educated guess with the limited information I have

You said it was a existing tunnel....and you have no info as far as dimensions, concrete thickness, air temp, etc? And to expand on what MotorCity was saying: you can get a laser thermometer pretty cheap.

BTW, if you have no numbers.....what is the basis for your statement in the OP that you "get too much displacement in the concrete due to rise and decrease in temperature"?

 

[JStephen]

One of the neater train-watching experiences I've had was visiting the East Portal of the Moffat tunnel. Entrance was closed off with a big curtain. Curtain opens, unit coal train comes out, coasting at that point, with 4 locomotives on the lead, two more halfway back, two more at the end. Then the curtain closed, big fans came on, and they blew black diesel smoke out of that tunnel for the next half hour. With that kind of operation, temperatures could potentially be all over the place, and the thermometer idea above sounds like the way to go.

 

[IRstuff]

The thermal mass of rock is pretty large, so unless you've got a wind tunnel, it's unlikely to shift the temperature by much

TTFN (ta ta for now)
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[bojoka4052]

Thank you for all those sources IRstuff, I cannot access the second to last link (weather365), but I believe I get your point; underground temperature is pretty constant, but what it exactly might be varies. But how do you take into consideration that the tunnel will have an opening at each end, will this just be cancelled out if we get far enough into the tunnel? Also all the traffic in the tunnel will probably matter for the temperature as it brings cold air? Hot air?

Also its not the rocks im worried about, but just that the concrete tunnel itself has been designed based on very conservative temperature data (outdoor structure in the shade). I dont plan on doing any hard calculations, but I wanna discuss this and see if there is anything I might not have thought of.

 

[miningman]

what is the elevation difference between the two tunnel entrances?? Is any of the tunnel driven thru rock or is it a totally man made structure??

 

[WARose]

I ran some quick numbers.....and unless we are talking something blowing in hot gasses (at high velocities) almost constantly.....I don't know that the differential is that much to worry about (from that). I suppose direct sunlight could be a issue (at the ends).

But (again) all this is based on a lot of guesses at your situation.

 

[bojoka4052]

I think its all through underground rock, but I cant see how the tunnel is not fully manmade? I think the elevation is approximately the same at both ends - how would this influence the temperature if the elevation at both ends were same or different? This is something I didnt even think about.


Is there any way I could get a look at those calculations or get a how to explanation?

 

[Kaniou]

Hello bojoka

If you could get your hands on the German document 'ZTV-ING-Teil-5-Tunnelbau-Baudurchfuehrung' you may find something helpful. Basically if I remember correctly, it mentions a difference of 10 C degrees between the entrance and the inside.

 

[bojoka4052]

Thank you Kaniou, do you remember at which chapter it might mention it? I find german to be a bit troublesome to navigate. I found these document, but cant seem to track down the full version:

"Zusätzliche Technische
Vertragsbedingungen und Richtlinien
für Ingenieurbauten
ZTV-ING

Teil 5
Tunnelbau

Abschnitt 3
Maschinelle Schildvortriebsverfahren"

and

"Abschnitt 1
Geschlossene Bauweise"

 

[Kaniou]

I also do not really speak German but the document I was referred to was

"Zusätzliche Technische
Vertragsbedingungen und Richtlinien
für Ingenieurbauten
ZTV-ING

Teil 5
Tunnelbau

Abschnitt 2
Offene Bauweise

 

[miningman]

BOkja, I think there are a large number of variables that you have not considered. Research " natural ventilation pressure" in order to get an initial understanding of how the elevation differences of the portals affects airflow and temperatures within the tunnel.