Actually the temperature wouldn’t have to be 3 times the normal level to melt the ice 3 times faster as the increase in temp could cause exponential melting rates with only an increase of 30-40 degrees.
On another note, the ice in real life wouldn’t melt at normal temp in even 11 turns if you calculated the size of the wall and determined the rate at which it would melt using the simple formula:
q=h*A*(T2-T1), where q is the amount of heat transferred, h is the heat transfer coefficient, A is the surface area of the block, and T2-T1 is the difference between the average air temperature and the temperature of the block of ice, taking into consideration that the heat of fusion (the amount of heat necessary to transform ice to water) is 80 cal/gram.
The key to melting ice is heat transfer and air is a poor transfer medium.
Also, since we are underground the normal ambient temperature is typically around 50 - 54°F year round in this environment, so even if the temp was 3 times normal it would be about 150 - 162°F; which is hot but survivable for short periods.
Just FYI