We want to clarify media reports that may have left you with the impression that the SR 99 tunnel access pit is unsafe. Despite what you may have seen or read, at no time has there been a “risk of catastrophic failure” due to excavation of the access pit.
Last week, the Seattle Department of Transportation and Seattle Public Utilities sent WSDOT a letter with concerns about construction and dewatering of the pit that will be used to access and repair the tunneling machine.
The City’s letter compares sentences from draft Dec. 11 and final Dec. 19 letters written by Seattle Tunnel Partners’ Engineer of Record on the access pit. These letters were between the contractor and its sub-contractor. An Engineer of Record’s role is to prepare a design and help assess potential risks for any work on a contract and make recommendations on ways to address those risks so they don’t materialize.
Before access pit construction began, STP and their Engineer of Record agreed to inspection procedures to verify the quality of the access pit work as excavation progressed to 90 feet below the ground surface. Procedures for excavation below 90 feet had not been agreed upon in December; they have since been finalized.
The Engineer of Record sent a draft letter to STP on Dec. 11 starting a technical conversation between the two parties about whether their current procedures needed to be adjusted for excavation below 90 feet. Both agreed that the procedures needed to be adjusted. The Engineer of Record then revised their draft letter and sent a final version on December 19 that stated excavation may not proceed until new procedures are adopted. This is a routine work and risk assessment process.
At no time did the Engineer of Record state that there was an existing “risk of catastrophic failure” due to access pit excavation. The correspondence describes what steps STP must continue to take to assure that they adequately address risk for the balance of the work.
STP is excavating and verifying their work in a manner that is consistent with the direction from their Engineer of Record – otherwise they would not be allowed to continue. This is a design-build contract which puts the responsibility of design and construction on the contractor. WSDOT’s role is to assure the terms of contract are met and to verify the quality of the work.
Our first priority is safety – period. At no time has the Alaskan Way Viaduct or the access pit been at risk due to excavation. The viaduct remains safe for vehicle travel.
WSDOT and the City have a shared commitment to public safety and to improve communication. We are in constant contact with representatives from SDOT and other departments at the City. We have provided access to all of our data and have weekly meetings where they can raise questions about the data they are receiving.
The City has access to real-time information, and we will work with the City to establish more specific protocols so that when there are questions about a project activity we both share data, expertise and context.