Unless there is some kind of weighing system that tells the exact weight any guess is the best guess. A load can be of 100t or 120 or 150 tonnes and for naked-eye it will remain a guess. If original design was for 70t then they should enforce it. They should have set up some kind of system.
On the other hand, if there is a use of low-quality material or there is the deviation from original design due to negligence, corruption, an inquiry should be held and those involved should be punished whether its engineer, contractor, administrator, politician or even CM.