The main cause as seen in the photo is under-reinforced lintel beam, this lintel has been cast by uneducated workers and not designed by a structural engineer, if it was designed by a structural designer it would not have failed.
The span is also quite big so they should have gone for a proper structural beam rather than a lintel.
Further the quality of the work is also shabby so such kind of bad quality construction is bound to fail.....Cheers
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