If the foundations of buildings are VERY DEEP, they are properly supported from solid earth far below the surface. In Bangkok, that means more than 30 metres depth. It's the sediments nearer the surface that are drying out and shrinking, so the ground surface is subsiding. If your building is not "growing taller," that is, adding more steps to get down to the sinking ground surface, then it is floating on the top of the shallow, contracting sediment stack. It will crack, or lean, sooner or later - and bad luck if a minor earthquake should rattle it.