On November 11, 1957, at 11:30 p.m., a break is reported in the 50-year-old Ravenna Trunk Sewer located in Seattle's Ravenna neighborhood. Within the hour, the cave-in of the six-foot brick sewer tunnel causes a sinkhole to appear in Ravenna Boulevard. The sinkhole gapes wider, and 10 families are evacuated out their back doors after midnight to prevent their being swallowed up. (The chasm on Ravenna Boulevard eventually grows to 175 feet wide, 200 feet long, and 50 feet deep.) Shortly after midnight, some 8,000 cubic yards of sand, bricks, and timbers flow a quarter of a mile through the six-foot tunnel. The Ravenna Trunk Sewer is the largest in the city, and sewer service is cut off in a 13-square-mile area in which 43,000 people live. This is the most costly sewer break experienced by any municipality in the country up to this time.
They Show Their Stuff
Some time after midnight, City Engineer Roy W. Morse sprang into action. He contracted with the Western Bridge Company, which had men and machines on site within hours. First they attempted to build a cofferdam, but this had to be abandoned, with the loss of a large mobile crane narrowly averted. Working around the clock, they then built a bypass sewer through Ravenna Park. This involved the building of a cofferdam at Brooklyn Avenue and Ravenna Boulevard, obtaining 5,400 feet of welded steel by-pass pipeline (from Seattle Water Department stocks of used pipe), and installing pumps. Service was restored by November 22, 1957.
Repairing the original brick sewer, which had been built in quicksand, presented severe technical difficulties and took months to complete. The quicksand had to be made stable and hard before it could be tunneled through. After trying several techniques that didn't work, project engineer Robert Burns proposed the Joosten Process. A modified form of this process finally worked to harden the sand. Sodium silicate (water glass) and calcium chloride were injected into the sand using high-pressure grease guns. This made the quicksand into a stable hard sand cocoon that could be tunneled into.
Nightmare Pothole Filled
The pit in Ravenna Boulevard caused by the cave-in was filled with 16,000 cubic yards of fill, brought in by barge from Steilacoom, trucked from barge to hopper, and then conveyed by conveyer belt from 17th Avenue NE to the center of the hole. Filling took 10 days.
The entire cost of repairing the cave-in of the Ravenna Trunk Sewer was $2 million. The work took two years to complete.
