Machine Tunneling on Missouri River Dams

The world's first successful large-diameter tunneling machines were developed at Oahe Dam after mechanical tunneling methods had been evolving at other Missouri River dams over a period of 20 yr. At Oahe Dam, specifications prohibited blasting through highly faulted shale; consequently, the contractor who was awarded the first tunnel contract devised a cutterhead type of machine that would mine the full face in one continuous operation and would permit erection of temporary supports near the heading. Despite mining problems encountered in tunneling through highly faulted shale, rates of advance were more than doubled by the use of these machines over the rates normally attained by conventional tunneling methods. Since their development at Oahe Dam, similar machines are being used throughout the world.