Once constructed , the bathtub walls relied on the presence of the basement floors of the WTC to give lateral support . When these were partially destroyed following the collapse of the Twin Towers during the September 11 attacks , it was feared that removing the resulting debris pile could weaken the walls and cause them to fail , endangering workers and possibly compromising other buildings and flooding a significant portion of the subway system . During the recovery and clean-up operation , dangerous degradation of the walls was discovered , prompting an emergency operation to install tiebacks to the bedrock to shore up the bathtub walls . Excavation of a new Bathtub was conducted between 2006 and 2008 , with the new Bathtub reaching underground
September 11 attacks
September 11 attacks
The Bathtub