From Vintage Seattle:
The night of Nov. 11, 1957, the largest and most expensive sewer collapse in the U.S. to that date occurred at Ravenna Boulevard between 16th and 17th Avenues NE. The hole was 60 feet deep but the sewer trunk in question is 145 feet below the street. Repairs took two years to complete, including first a sewer bypass through Ravenna Park, then stabilizing the broken trunk with a newly devised grout material and re-boring the tunnel.
Just to make a comparison, the now famous Guatemalan sinkhole is estimated to be 60 feet wide and 30 stories (approximately 300 feet) deep.
