Well, if they were burried in the ground, I'm sure the explosion would have been bigger. But, just laying on top of the ground, most of the damage is going to be propelled upward, so that's still pretty impressive to blow that large of a crater in the ground.
Well just becuase there were 17.5 ton of explosives doesn't mean you'll get a 17.5 ton blast. Thats freaking nuts though. Crazy nobody was hurt. Did anyone notice there's no truck to be found!