Phase 1 of the Second Avenue Subway was constructed between the Lexington Avenue–63rd Street station on the 63rd Street Lines and an existing tunnel segment between 99th Street and 105th Street, with a terminal station at 96th Street. In Phase 1, tunneling was completed between East 63rd Street and East 92nd Streets through the use of TBMs. The TBM launch box was , and is now part of the 96th Street station. Two access shafts were constructed for the 72nd Street station. Slurry or diaphragm walls, wide and long and about deep, were built alongside the sections between East 93rd and 95th Streets. Since the rock is shallower between East 91st and 93rd Streets, secant piles did the same work at shallower depths. Earth excavation was conducted between walls once they were installed, and box structures were built using a bottom-up construction method. Temporary decking constituted the top of the boxes, and the decking both braced the excavation and supported the walls and Second Avenue traffic.