The big tracked excavator in the background, the one atop the pile of rock, was scooping up loads of rock and dumping it into this tracked dump truck. (Googling around says this is technically a "crawler carrier" with a "dump chute", I guess?)
The dump truck would then trundle its load along the canal to the other tracked excavator, which would scoop it out and use it to reline the banks. It'd drop a couple scoops and then use its bucket to... WHAM! WHAM! WHAM! ...smoosh the rocks it had just dropped into the bank of the canal.
