Called “sheet piling,” this wall is in place. Much of it, however, still needs to be pounded farther into the riverbed. That is what crews are working on as construction of the Riverwalk enters its 21st week.

More steel “H pile” beams still have to be installed between State and Dearborn Streets and between Clark and LaSalle Streets. Old concrete is still being removed from all three blocks of the current construction phase. More rods and walers will be installed to hold the sheet piles in place.

The Chicago Department of Transportation keeps pushing back its estimate of when the much anticipated drilling of caissons will begin. In his report on Friday to neighbors of the Riverwalk, CDOT construction manager Oswaldo Chaves included “installation of the foundation caisson east of Clark Street” in planned work for the week of June 1.

On Tuesday, a diver was spotted west of the State Street Bridge. Divers have been inspecting the bottom of the river in preparation for caisson drilling that will secure the new Riverwalk to a limestone shelf that stretches to Niagara Falls.

The first caisson will be 75 feet long and six feet in diameter.

(Left) A diver emerges from the Chicago River west of State Street on May 27. The diver spoke with crew aboard a tugboat owned by Jack Tanner Towing Company. (Click on image to view larger version.)

(Right) This photo supplied by CDOT shows backfilling east of Clark Street on May 27. A clamshell bucket attached to a crane is dumping crushed aggregate into the water between the old Riverwalk and the new river wall. This is currently being done between Dearborn and LaSalle Streets. (Click on image to view larger version.) As the clean, finely crushed stones go into the river, the water is filtered to remove sand and concrete, contaminants that turned the the water light green. (Below) The aggregate arrived in March on a barge.