A single tunnel shows significantly greater responses under earthquakes in comparison to static condition. What is the reason behind this significant increment?
Hello Sumee tabassum Amin
some causes can determine the conditions you have observed.
Referring to stress levels ("forces") outlined for example in numerical modelling, one could list:
- different combinations of possible loading schemes
- different values of static - dynamic moduli between surrounding formation and concrete (shotcrete) lining
- dynamic (short term) loading without immediate redistribution of stresses
- expected high concentration in zones where a change in geometry is relevant (corners, different thickness, presence of ribs in primary lining etc)
Consider that seismic induced stress is affected by mass of vulnerable elements; some useful observation could arise also from displacement calculated form the model.
Hope these suggestions can help your interesting question.
Regards
C.O.
The main reasons are as follows:
- Earthquakes generally act as shear forces affecting different parts of tunnels.
- These shear forces have lateral and vertical components which can act simultaneously on different sections of tunnels.
- The combination of horizontal and vertical components of earthquakes can generate areas of high stress concentrations.
- Dynamic actions are generally more cumbersome and more destructive than static actions.
To resist all earthquakes actions (dynamic actions), tunnels must develop strong adequate responses (high internal forces). Otherwise, their failures may be imminent.
Accordingly, tunnels must have enormous and sufficient resistance to withstand earthquakes attacks.
Hello Wadslin
just to understand, but to mention that "shear forces have lateral and vertical components" seems a misunderstanding, because in structural mechanics shear is applied as "lateral" component, while vertical component is intended as normal action to the body. In other words, global force applied to a body has components.
If I have correctly understood your post, otherwise, sorry.
Regards
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