It would seem that the clay/earth mass of the dam is intact. Calculations have shown that the mass of dam is more than the force of contained water pressure.
The cracking and damage was to the "spillway". It's the concrete cover that conducts excess water away when the dam is up to level.
Over time, water has crept under the concrete and damaged it. Hence why they are adding bagged mass , simply to reinforce the spillway.
As usual in this country, the problem is not with the installation itself, but with lack of continuing maintenance.