Hypothesis for the effect of an explosion

Each house had 9 barrels of explosives placed in it for a controlled explosion. The first house being above ground was blown to smithereens. The second house which was half submerged had its roof blown off but sustained no major damage to its foundations because of the dampening effect of water. The third house which was fully submerged was crushed by an implosion due to the low pressure created by the explosion of the barrels.