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[ New Search ] Chicago Subway System: Mining the Tubes in the Loop Section Location : Chicago, IL Date : Jun, 1940 Agency : PWA Owner : NARA (SPB) Medium : B&W Photo Control Number : P-3282 Enlarged Image Description : PWA is financing the construction of the first subway system in Chicago, a 7.7 mile double tube system consisting of two routes, State Street (Route 1) and Deerborn Street (Route 2). In the loop sections of the two routes, the tubes are being mined by the shield method because of the high water content of the soil, and the weight of the loads on the surface. The shield is a huge device 20' long, 25' wide, weighing 225 tons, that is pushed through the soil by means of hydraulic power. As it moves, the clay squeezes out toward the rear through six ports, where it is mined by hand knives. This is a view of one of the two shields in Route 1. Listed Under: [Transportation][Subways][Chicago Subway System]