What are the liquefaction effects on tunnels? For example, I'm thinking of downtown Seattle, where they are constructing a new tunnel in an area that is labeled as susceptible to liquefaction. How does the tunnel change the way the ground reacts?
The tunnel will collide with the soil. Thus, likely cause concentrated loads and deformation sufficient for liquefaction. From that point onward everything is a two-edged sword. Liquefied soil becomes softer while liquefied, and remains softer after liquefied. Soft is bad because the tunnel has less support, uneven stress distribution may happen... Soft is good because the tunnel is damped, and if the soil happens to move - the loads shear forces will not be as concentrated. Then again, the undrained response has a higher strength (caused by dilation), and density increases after draining thus even drained soil become stronger... Soil strength is good because it holds the tunnel in place. Strength is bad - because it causes impact loads, and additional loads if soil masses start moving relative to each other... Depending on how many times the soil was liquefied, the soil remains disturbed - sensitive to repeated liquefaction (substantial increase in resistance to liquefaction requires a rather large increase in density). This can be both good and bad, again.... Also, non-liquefiable soil can be disturbed back into the liquefiable state during yielding - its a full circle of losing and recovering disturbed soil states. It requires capturing both loss and recovery of stiffness, strength and volumetric response... both loss and recovery of all properties need to be accounted for. Disturbed soil states are preserved during long-term settlement. Long after an earthquake disturbs the soil, small amplitude loading cycles will cause gradual re-stabilization. thus localised settlements will continue developing along the length of the tunnel, long after the earthquake is over. There's really a lot happening there. It is all nonlinear and complicated... and invisible to the naked eye. It's fascinating :)
![[4K] Watch SpaceX Catch A Starship Rocket From Space!!! #IFT5](http://i.ytimg.com/vi/pIKI7y3DTXk/mqdefault.jpg)
What are the liquefaction effects on tunnels? For example, I'm thinking of downtown Seattle, where they are constructing a new tunnel in an area that is labeled as susceptible to liquefaction. How does the tunnel change the way the ground reacts?
The tunnel will collide with the soil. Thus, likely cause concentrated loads and deformation sufficient for liquefaction. From that point onward everything is a two-edged sword.
Liquefied soil becomes softer while liquefied, and remains softer after liquefied. Soft is bad because the tunnel has less support, uneven stress distribution may happen... Soft is good because the tunnel is damped, and if the soil happens to move - the loads shear forces will not be as concentrated.
Then again, the undrained response has a higher strength (caused by dilation), and density increases after draining thus even drained soil become stronger... Soil strength is good because it holds the tunnel in place. Strength is bad - because it causes impact loads, and additional loads if soil masses start moving relative to each other...
Depending on how many times the soil was liquefied, the soil remains disturbed - sensitive to repeated liquefaction (substantial increase in resistance to liquefaction requires a rather large increase in density). This can be both good and bad, again.... Also, non-liquefiable soil can be disturbed back into the liquefiable state during yielding - its a full circle of losing and recovering disturbed soil states. It requires capturing both loss and recovery of stiffness, strength and volumetric response... both loss and recovery of all properties need to be accounted for.
Disturbed soil states are preserved during long-term settlement. Long after an earthquake disturbs the soil, small amplitude loading cycles will cause gradual re-stabilization. thus localised settlements will continue developing along the length of the tunnel, long after the earthquake is over.
There's really a lot happening there. It is all nonlinear and complicated... and invisible to the naked eye. It's fascinating :)
It’ll be like liquefaction except this time with a tunnel where before there was not a tunnel.
Hope this helps.