WSDOT and Seattle Tunnel Partners gave an update to the Seattle City Council this morning on the Viaduct condition, the SR99 tunnel, and ground monitoring.
WSDOT’s slides are here.
First topic: the Viaduct status. Tim Moore, lead engineer from WSDOT who works in the Preservation office, presented. WSDOT performs weekly and monthly high-precision surveys of the columns, and Seattle Tunnel Partners has an automated monitoring system that give updates every 20 minutes. Plus, twice a year WSDOT does an in-depth inspection, and this morning they reported on the recent inspection (Oct 31/Nov 1). They did see some additional settlement near Seneca, between a quarter and half an inch on the west side (previous settlement was on the east side). In the Seneca area they have also seen some cracks in previously-repaired expansion joints, which is probably also related to the settlement.
Context: they have only been monitoring settlement since 2001. The Nisqually quake caused an immediate 6 inches of settlement, and since 2001 they have seen 2-3 inches of settlement in certain places.
They are approaching the Viaduct monitoring and ongoing repair with the perspective that this structure is on its way to eventually being torn down. They feel confident that it is safe now though trucks are restricted to the right lane an overweight vehicles are further restricted. WSDOT gives bridges a sufficiency rating of 1-100 based upon its condition and sufficiency for its purpose, and the Viaduct rates just over 9. Partly this is due to lack of certain features like shoulders, but also because of a lack of reinforcing on crossbeams and ongoing corrosion of steel beams. Restricting trucks to the right lane places them on a stronger part of the structure and eases the overall strain on the bridge.
Next up: Chris Dixon of Seattle Tunnel Partners, project manager, presented on the status of the SR99 tunnel project. Since August they have been reconnecting the front end of Bertha and re-testing. They claim they have reconnected everything and are performing the “no load” test: making sure everything works and has been reconnected correctly. Lots of testing and measuring to ensure that all clearances and tolerances are met. They are at the final stages of the “no load” test; next they backfill the shaft — with sand until they are about 4 feet above Bertha, then with the materials that they dug out of the shaft. Then they run “load tests” in the shaft. They have about 20 feet of mining while still in the shaft before they hit the north wall. From there they will continue forward in late December until they reach a point designated as “Safe Haven 3” in late January when they do planned maintenance. From there they begin tunneling under the Viaduct, with completion of tunneling in January 2017. Their target for having the tunnel complete and open for traffic is April 2018.
A side note: the contract with Bertha’s manufacturer, Hitachi Shosen, specifies the final payment after the machine has tunneled 1500 feet (or 200 rings installed). Currently they are at 1000 feet and 158 rings, so they haven’t received their final payment. There are warranties, service contracts, etc. as part of the contract as well, and Dixon reports that Hitachi Shosen has been very involved and responsive in the repair efforts.
Construction on the south tunnel entrance is almost complete, and likewise for the north tunnel entrance. Once the tunneling is complete they need to finish the “access pit” at the south end where soil is removed and rings are brought in, and the “receiving pit” at the north end where Bertha will end up and will be lifted out. This work represents about 1/5 of the entire project.
Council mmeber Bagshaw asked Dixon why he has confidence that we’ll now have a tunnel boring machine that can complete the job. Dixon replied that his confidence comes from the quality of people involved and the level of detail in the plans. Hitachi Shosen designed a new seal mechanism to replace the broken one, and they have added steel reinforcing to manage changes in the load forces the machine will be under while operating. So in some ways it’s a different machine with some new components. Also, with the redesigned seal system, if they need to do anything to the seals from this point on they are much more accessible without needing to dig a new pit.
Council president Burgess asked “What went wrong?” and Dixon responded that there are 6-7 theories as to what happened. Burgess followed up by asking How do you know it’s not going to happen again if you don’t know what the cause was?” and Dixon replied that the work they have done has addressed the several most likely causes. Dixon danced around the fact that there are several lawsuits pending and so he is unwilling to go on the record as to what he believes the cause was (WSDOT has not released a description of their theory).
David Sowers, deputy program administrator for the Viaduct replacement program, presented on the ground monitoring program for the tunneling project. When the access pit is filled in at the end of the month, they will turn off the four dewatering wells that have been controlling water seepage in the pit. They also do ground monitoring throughout the Pioneer Square district, and they will pay particularly close attention to any settlement when they start turning off the wells. They are not expecting any changes, though. They also did outreach to the Pioneer Square Alliance so the local businesses know what’s going on. They have seen some settlement that seems tied to the drought, and the recent rains seems to have stabilized that settlement.
The “north access” to the tunnel (surface streets, onramps and offramps) is currently about 80% done and should be largely complete by next summer (with the balance done after the tunnel is complete). They also plan to do a bunch of lane and signage work on Aurora between the tunnel and the Aurora Bridge starting in mid-January, with one lane closed around the clock for 7 weeks southbound and 5 weeks northbound (and additional lane closures at night).
Bad news: John, Thomas and Harrison can’t be reconnected until the tunnel is complete and opened; so that’s been delayed until 2018.