Hi Kim, yes the tubes are filled with concrete. Their main purpose is as footings for the waterfall wall, but should provide some stability also. The contractor also mentioned inserting styrofoam somewhere along that side, which will act as a buffer to absorb pressure when the ground water freezes and expands in the winter. When i get home from work tonight the collar forms should be done, ready for concrete tomorrow.
btw he was feeling better today, also i left him water and soda on ice and a couple snacks