I discovered that if I zoomed in and then focused manually the screen was nearly invisible. That entire device on the left is the boring machine. All if it advances through the tunnel as the blade grinds away at the front. The tailings are carried away on a conveyor (the blue structure along the center; it doesn't have the belt installed yet). A separate conveyor will bring the concrete wall segments to the front. The borer has a mechanism that picks up the segments and puts them into their proper positions around the circumference of the tunnel.
Capital Hill StationConstructionLight Rail StationCapitalHillStation5163
From Sound Transit Capital Hill Station