As I did my homework, and to cover my bases against Tann's sly DM mind, here is a little factoid on the weight tolerance of ice in the real world...
Ice thickness = 8" - 12" (20 - 30 cm) - suitable to hold one car, group of people (approx. 1500 - 2000 pounds)
So 11" should be plenty thick to allow a group of people to pass across it.
Now don't go crazy with your dice Tann!!