@TopCat can answer the question if soil boring tests have been conducted or not. Burj Khalifa borehole tests were done up to 80 m below the ground.
---------------------------------------------------------------------------------------------------
Who told you Sears Tower is floating on swamp? Do not speak false of a subject that you just do not know. Structurally, the building pioneered the use of bundled tube construction. The tower is composed of nine bundled structural tubes resting on reinforced
concrete caissons that go down
to bedrock. Now, you will come out with your own personal definition of caisson.
Read also post #19 to know about the foundation system of Burj Khalifa in Dubai. Who told you it is on the soft sand? Do not please utter again the words, clever engineering, when you do not know even the requirements of a strong geology for high rise buildings.