Parkway Cave In

This is a hole that suddenly appeared on the parkway in front of my building. I did not put the cigarette butt in the frame for scale but it does the trick. It's about 7 or 8 inches wide and goes down several feet and back under the sidewalk. The wash out under the walk looks fairly extensive. I have contacted 311 3 times and have been told they'd make a report. So far I have seen no response. I put a bit of garden fencing around it to keep people from stepping in it. If noone comes to investigate soon, I will try contacting the ward office.