In order to start building the World Trade Center, more than 900,000 cubic meter of material was excavated and a slurry wall was necessary to prevent water seeping into the footing site. All excess material excavated was used to extend Manhattan shoreline. The world trade center construction used a groundbreaking technology using two 'sky lobbies', floors designed on which people could switch from an express elevator to a local elevator. The structural frame of the WTC buildings was made of tube-frame systems, allowing larger open floor spaces than traditional methods. Along with this system, the building also was built using high-strength load-bearing perimeter steel columns called Vierendeel trusses. The core formed by the building was a rectangular area 87 by 135 feet, with 47 steel columns with an extensive use of prefab modular pieces. The general contractor on the World Trade Center initial development was Tishman Realty & Construction Company.
The process of cleanup and recovery continued 24 hours a day over a period of eight months, being completed several months ahead of schedule.