Geological Survey investigations in the U12b.01 tunnel, Nevada Test Site

The U12b.01 tunnel is part of the U12b (Rainier) tunnel system driven northwestward from the east slope of Rainier Mesa (figs. 1 and 2). Geologic and geophysical studies in this tunnel were conducted by the U.S. Geological Survey on behalf of the Albuquerque Operations Office of the Atomic Energy Commission. This report includes a brief description of the stratigraphy and structure, and data on petrology, mineralogy, and chemical and physical properties of the rocks that are exposed in the tunnel.

The U12b.01 tunnel trends N. 10° W., and connects with the Ul2b tunnel at about 500 feet from the portal (fig. 2).  The U12b,01 tunnel is about 250 feet long and contains an alcove 40 feet long and 20 feet wide, and a shot chamber 17 by 20 feet. The tunnel is irregular and ranges from 6 to 15 feet in width and averages 7 feet in height.  Much of the tunnel has been supported using 6-foot steel sets and wood planks for lagging Vertical and minimum cover over the shot chamber at west end of the tunnel are approximately the same, about 295 feet.