Among the reinforcements the protagonist brought, there were special forces, riot police, and bomb disposal experts. But there were too many mines buried; the first wave of explosions sealed the exit, intending for everyone to be buried with it. The second wave of explosions was just five minutes after the first.
Actually, the bombs made locally were not hard to defuse, and the protagonist brought enough bomb disposal experts to handle it. The key was the large number, and they didn't know where they were buried or how many were buried. At the crucial moment, the heroine, who knew the details, informed them of the bomb locations. The bomb disposal experts handled them based on the locations reported by the heroine and indeed dismantled most of the dangerous explosives, but still triggered one or two.
