Today, the ground beneath Grand Central Terminal houses New York's second-busiest subway station, but in 1916, commuters could only dream of shuttling around in tunnels as storied as this one. At the time, construction workers and engineers were struggling to install the Lexington Avenue line without disturbing traffic on ground level. Digging subway tunnels was a tricky business, especially in areas like Grand Central where workers had to dig around existing subway lines. Quite frequently, they would encounter "rotten rock," or weak strata, which would collapse temporary structures and trap builders underground. Engineers also had to deal with underground water, which would frequently convert the floor of construction sites into quicksand. At the corner of Broadway and Canal street, engineers installed a set of pump that removed 20 million gallons of water a day from just one spot. Meanwhile, near Grand Central, New Yorkers watched in horror as a temporary street collapsed into a tunneling site, taking a truck, a streetcar, and several pedestrians with it.
Read the full story in "The Giant Task of the Subway Diggers in New York"