is it true that blasting the entrance of a tunnel locked in pressure to keep the sides intact, and once closed tunnel is opened, in a few days, it begins to collapse?
No you don't have to blast the entrance. just in our site here, we encounter a closed tunnel, in the entrance we found a diagram stone which is the same form with the tunnel. the openings are in both sides and at the back. But the our operation was stopped due to our diggers having nightmares. they said that there's a tall man wants to kill them. two of my diggers almost the same story about their nightmares.
Atan, read the post of Kaloy again. What he was saying, when the Japanese Sealed off the Tunnel by Blasting the entrance, the pressure resulting from the Blast was sealed inside the tunnel when the tunnel entrance collapsed and thereby sealing the entrance. When the tunnel was opened, the tunnel, he says, begins to collapse after a few days because he thinks the pressure inside the tunnel was released after the entrance was opened. My answer was NO as the tunnel is normally earthen material and earth is porous, meaning it will not stop or seal in Water nor Air. Hopefully my explanation clarified the matter.
Not exactly. As a Structural Geologist, there is a couple of factors involved. A tunnel that has remained open from the start has a natural rhythmic exchange of air with the outside. This includes, moisture and barometric pressure. A closed tunnel has a predominately flat line moisture and barometric pressure changes are modulated to very long periods. On the micro level, moisture creep (that means changes up and down in percentage saturation) will make the soil or rock expand and contract, this is exaggerated with barometric pressure changes such as weather fronts passing by. A sealed tunnel gets stabilized to the very small changes due to it's isolation. Once the tunnel is opened up to the outside atmosphere, the tunnel walls start to creep. This is when the surfaces start to exfoliate, that meas flake off in spots up to extensive failure as in a roof collapse. It is a well known fact to miners and geologists that once opening a formerly sealed old tunnel, the tunnel will start to destabilize in about 3 weeks, that is about 21 days. This is an approximate. We have always had a rule, once a tunnel is opened up, the freaking thing will start falling apart in about 3 weeks. So get in and get out fast. The longer you wait, the greater a chance for a collapse and getting caught inside alive. I have opened several sealed tunnels in the islands and the results are always the same. Another factor that can be a problem is developing water intrusion. A sealed pressure tunnel may resist water intrusion. Once the tunnel starts to breath, water intrusion may very well develop and steadily increase. Been there and done that unfortunately.
Z
