Engineers also should be very well aware of the actual construction by now - given the exposed evidence of the broken spillway. IT makes perfect sense to take these measures.
What they are doing now is correct & is the right action(s) to take. I believe they will address any subsurface risk with possible coring to emplace sub void fixing materials if needed.
comment only: However, whomever was in charge years prior, they should have been doing this exact same work to prevent the main spillway failure. They had the warning sign/alarms (excessive water in drains, missing water, & crack patterns).
Crews using Ground Penetrating Radar on Main Spillway - Looking for voids, unseen cracks, erosion…Plus sealing joints.. note the red marks carefully delineating each run (x & y).
Engineers discussing a long crack in the Upper Main Spillway (note this angle of crack is the "herringbone" pattern angle that has followed underslab drain pipe placement). Note their tilt from the spillway angle.
