I realized later
that it was only a walk on the path across the terrace toward our door that would make the big slab of concrete bump against the steel-reinforced industrial-strength (grocery store/shopping mall below) superstructure and then tip back. In other words, the path to our door always tipped it and since it was slightly heavier on the other side, it tipped back; ready again.
I recognized that the feeling I got when I heard that sound had no remaining useful function.
I got a bag of sand from beside the river. I dusted the sand back and forth along the cracks between the large concrete squares, letting it settle in while I teetered the tottering slab back and forth upon its axis of balance....