 The tunnel proved to be a constant nuisance to the Chicago Great Western and its predecessors . Almost immediately , railroad engineers realized that the unstable nature of shale through which the tunnel was bored , ground water seepage , and the isolated location of the tunnel meant repairs would be frequent and costly . The tunnel was originally <unk> by wooden beams when it opened to rail traffic in January 1888 , but these eventually proved inadequate , to be replaced in 1902 by brick and reinforced concrete . Constant deterioration of the supports meant large @-@ scale reconstruction of the tunnel would be needed again in 1912 , 1918 , 1944 and 1947 . 
