The first picture is of the Engineer Corps. Notice the oil lamps on their hats which they used to light their way.
This second picture is from the river tunnel taken May 9, 1907. According to the caption on the back of the photo, the two men on the right are inserting the "caulking mixture" into the joints; the two men in the middle are "hammering mixture in"; and the two men on the left are "tightening bolts after putting on grummets, grummets soaking in red lead in front."
This third picture depicts "dumping car used to place concrete below track level," according to the caption.