January 13, 2016One of the barges Seattle Tunnel Partners is using to haul away excavated material began to list or lean to one side as STP crews loaded it early Tuesday.To prevent damage to the conveyor system, STP released the barge from its moorage at Terminal 46. Some excavated clean soils were spilled into Elliott Bay. The barge then drifted into nearby Pier 48, which is owned by WSDOT and slated for demolition.The barge has since been moved to the west end of Terminal 46. STP crews are working to transfer the material on the barge to another barge. STP is inspecting Terminal 46 and Pier 48 to determine if any damage occurred.Tunnel excavation is temporarily on hold as STP addresses this issue. We’ll provide additional updates as we receive new information.
Governor Inslee has put a hold on drilling until the cause of the sinkhole is determined.Seattle Tunnel Partners resumed mining Tuesday evening, using trucks to remove excavated material while they continued working to resolve an issue with a soil-removal barge. STP crews resumed excavation at 7 p.m. Tuesday.Approximately two hours later, a sinkhole developed within STP’s work zone near South Main Street, about 35 feet north of the access pit. It is located more than 100 feet south of the cutterhead's current location, in ground that crews mined through last week. STP filled the sinkhole overnight with 250 cubic yards of concrete.This section of the tunnel drive is protected by an underground wall built by STP before tunneling. The wall was designed to isolate ground movement and protect the nearby Alaskan Way Viaduct. A manual survey of the viaduct conducted after the sinkhole developed found no movement. WSDOT and STP will continue surveying and monitoring the ground, viaduct, utilities and other structures.The cause of the sinkhole is still under investigation. STP is analyzing the portion of the tunnel that crews have excavated since mining resumed. There is no indication that any other locations have experienced ground loss.
So, to recap, in two days we lost a barge, rammed some piers and caused a sinkhole after traveling about 30 feet. What is so disturbing, is that the sinkhole could have appeared under the viaduct, the elevated highway in the photo. Seattle is planning to shut the viaduct down for two weeks as Bertha tunnels underneath. I think this is a really good idea for the safety of the motoring public. I am so glad we sold the West Seattle house, after the Nisqually earthquake in 2002, they closed the viaduct. We couldn't leave home due to the traffic caused by the closure.
Here is a better shot of the rescue pit which I screen-scraped from a Bloomberg article. The Bloomberg piece is interesting in that it continues the myth that removing the viaduct will "open up" the water front. One hates to point out that the water front is entirely built up and the best place to see the water is from the viaduct, or some other elevated place.
So, here is your Bertha update for the new year. I will close my tale of tunneling woe with a hummingbird to lighten the mood.