Common sense dictates that you don't want to be anywhere near a concrete pylon when the load it's bearing is too much: when all that weight comes crashing down, you'll find out quickly how much weight your body can shoulder as well.
But if that wasn't reason enough to stay away from structurally unsound foundations, Phil Plait from Slate's Bad Astronomy documented another at the University of Illinois at Urbana-Champaign's Engineering Open House Day. There they demonstrated a machine that can stress-test materials with up to 3 million pounds of pressure. The concrete only lasts until the 1.6 million pound mark (start at about 1:30 to skip to the fun part), but do you think that 800-pound block of concrete just crumbles under the weight? Think again. [Laughing Squid]