Even if the number of Aliens in this area wasn't overwhelming, when they rushed from their various lairs towards the explosion site, their numbers were still considerable. Especially since some of the Aliens seemed not too intelligent, attempting to force their way through rocks when their own kind couldn't squeeze past.
Normally this wouldn't be an issue, but the problem was that Zheng and Jiang were not the only ones in the underground lairs. So, when too many Aliens got stuck and were unable to open up the heavy rocks, small bombs came in handy.
While setting off bombs on one side and coordinating with the other, explosions were heard from three different locations—now no one had time to mind others as everyone was only thinking about how to save themselves. Therefore, there was no restraint in using the explosives, and coupled with the fact that the area above them had just been thoroughly tunneled by Unit 114, the combined efforts led to the collapse of a stone belt!
