For most of 2012, the Washington Department of Transportation was watchdogged by KOMO News because of cracks found in new pontoons for the new 520 bridge. Now the Seattle Times‘ Mike Lindblom reports that Bertha, the 7,000-ton tunnel boring machine, purpose-built for digging the SR 99 tunnel beneath Seattle, sustained damage during its initial testing in Japan.
A January 23, 2013, update from WSDOT read, “She was performing well until last week, when crews discovered that something wasn’t quite right with her main drive unit, which rotates the cutterhead. It appears there was insufficient clearance between a rotating and stationary portion of the main drive unit, which resulted in damage to some of its components.”
Said Lindblom: “Testing was to be finished Dec. 25. As of this week, Hitachi Zosen crews in Osaka are disassembling and diagnosing the drive system.” (Sidebar: Although Bertha is, for a little while, the world’s largest-diameter TBM, it’s not a Big Bertha reference; the machine is named for Bertha Knight Landes, Seattle’s only female mayor.)
Bertha’s Twitter account has so far made no reference to its need for repair, or who’s paying for it. But in fact taxpayers are not on the hook yet. Seattle Tunnel Partners (STP) doesn’t officially take ownership of Bertha from Hitachi Zosen until the TBM has made it through about 1,000 feet of Seattle soil with no issues. Even then, says said Linea Laird, WSDOT’s administrator for the Alaskan Way Viaduct Replacement Program, “More than 90 percent of STP’s work will be performed for a fixed price.”
Meanwhile, cracks in pontoons and mistakes in construction continue to plague WSDOT’s 520 bridge replacement project. In December, WSDOT announced that although specified “hooked” rebar had been left out of three pontoons, they would “structurally adequate” anyway. That omission is, of course, troubling because the rebar in question was supposed to help prevent cracking due to stress.
In an earlier update, in mid-December, titled “Continued progress on SR 520 east approach bridge piers,” WSDOT mentioned that part of that progress was tear-down of a new 58-foot-tall concrete column that had been built with too little concrete over its reinforcing steel skeleton. That was on contracting team Kiewit/General/Manson’s dime.
The state has been pressing for an ambitious finish to replacement of the floating section of the bridge, by late 2014, which presumably was a factor in transportation chief Paula Hammond’s decision not to reject the cracking pontoons shipped so far, proclaiming them mostly cosmetic and of no danger to pontoon integrity. But today Mike Lindblom noted on Twitter:
Intriguing, and expensive. @wsdot is considering extra post-tensioning (transversely) to close remaining @520_bridge pontoon cracks. #WAleg
— Michael C. Lindblom (@MikeLindblom) January 24, 2013
