The Alaskan Way Viaduct tunneling project was in the news late last year when settlement of the Viaduct was reported during the dewatering efforts for the Bertha TBM rescue shaft. A recent post by WSDOT makes it clear that the settlement of the viaduct has been a problem for many years before the start of construction. The most recent round of monitoring by WSDOT began in 2001 after the completion of repairs to the the Viaduct following the Nisqually Earthquake. By 2006, a total of 4 3/4 inches of settlement had been recorded at one location. It appears that the rate of settlement is on the order of about 1/8 inch to 1/4 inch per year. I am sure the dewatering around the access pit didn’t help the problem, but it looks like it didn’t create it by itself either. This information just underscores the importance of the tunnel project to replace this aging structure. [Source: WSDOT Alaskan Way Viaduct. Image: WSDOT and STP via KPLU]
