The photos below show the drill rig boring the 48" caissons for the center bridge pier. The holes are 32 feet deep, with the last 16 feet being drilled into solid bedrock. Then the rebar cage is lowered into the hole, through the temporary upper sleeve. The sleeve stabilizes the drill hole and is retracted when the hole is filled with concrete, assuring there are no voids in the sides of the caisson.
The following photos show the caissons being drilled for the West abutment. These caissons are 30 inch diameter and are drilled to a depth of 58 feet, the lower 15 feet drilled into solid bedrock. The process is the same as that for the center caissons.
These last two photos show the East abutment foundation being formed on cleaned bedrock.