Sadly it's not possible to display anything underground, Although there is a way around it. Your option is to create a 3D Model of the Mines, and then position the models in the air, above the actual sites. Also, however deep the mines are, is the distance you could place the model above the surface.
Here's a good example: http://www.gearthblog.com/blog/archi...in_google.html
Hope that Helps.