Your structural engineer friend seems to have leaked confidential and sensitive information about his company to you. If proven to be false, your friend and his firm can be sued by the developer for either defamation, or breach of confidentiality agreement, or both. He has to prove, on balance of probabilities, that his assertion about the structural integrity of the building is technically correct.

Is he in a position to do that now? If he is in a position to do that now, and therefore his assertion is proven to be true, surely the authorities or the contractor would have cordoned off the construction site for safety reasons by now.

Building's foundation being held up by compressed sand and gypsum? ... as advised by whom? The structural engineer or geotechnical engineer?

There will be a three-day "Exhibition on Construction" between the 28th and 30th April 2009 at the Qatar Exhibition Centre. You may wish to get free and expert advise from the exhibitors on foundation failures and their remedies.