Simplify the following text for a Grade 11 native English-speaking person.
Original: The power of the explosion , which surprised even gunpowder experts , was such that seven-foot deep solid concrete walls ( made deliberately to replicate how archives suggest the walls in the old House of Lords were constructed ) were reduced to rubble .
Simplified: The power of the explosion was such that the 7 f deep concrete walls ( replicating how archives suggest the walls of the old House of Lords were constructed ) were reduced to rubble .