El Chapo's pyramid

Recently, El Chapo, the leader of Mexico's Sinaloa cartel, was in the news for his incredible escape from the high security Altiplano prison. Over the course of months, members of his cartel dug a tunnel 30 ft underground from a decoy warehouse to the space directly below the shower of his prison cell, almost one mile in length!

To dig such a tunnel, one must remove dirt as one goes along, and store it outside of the tunnel. Suppose the dirt was piled in a cubic warehouse, built specially to store the dirt. If Chapo's escape tunnel measures 1.5 km long by 1.7 m high, by 0.75 m wide, what would be the required side length ( $l_w$ ) of the storage warehouse (in m)?