A personal commentary about the SR99 Alaskan Way viaduct replacement TBM tunnelling project in Seattle last week by Lok Home, President of The Robbins Company, stimulated several points of feedback some on the record, some with the source withheld. Each contributes to the open discussion needed for advancing the process of learning from experiences.
The day-to-day management of the situation in Seattle belongs to the individuals and companies involved and trial by media is certainly not something to advocate. The overall experience however, belongs to everyone in the industry with an opinion.
This is the stance that project owner WSDOT adopted and has followed from the beginning of what is the long process of replacing the highway viaduct that was earthquake-damaged in 2001. WSDOT, the Washington State Department of Transportation, has been as open and as engaging with the general public and citizens of Seattle as it had to be for a project of such magnitude and significance to the general public and within the very heart of the city. The project’s public relations department has responded to all media enquires, senior managers of the project have been made available for regular media interview opportunities, and there has been open access to high level public meetings that discuss the project and its current situation.
TunnelTalk along with many other technical trade magazine and local newspapers, The Seattle Times in particular, has reported and recorded developments as they have unfolded across the current construction phase and through the previous years, and as investigated and probed by the journalists. This maybe uncomfortable for those in the spotlight, but that too is a learning process. As more underground infrastructure is to be built under the heart of major cities of the world, the industry has to be prepared, like other industries, to answer for itself, be open to the discourse and engage with the overall process within the industry to profit by experiences. The industry wants a higher profile for its achievements to overcome the ‘out of sight, out of mind’ complaint of old. It needs then to shoulder the focus of attention and be as open as possible in return. When professionals in the industry and others speak, it is in its interest of the industry to be aware of the opinions.
To that end, TunnelTalk published the personal commentary by Lok Home last week and has published commentary about the SR99 project by others as well. Notably, in our report of the WTC2013 conference event in Geneva, Switzerland, we published comments of the discussion period after presentation of a paper about the mega machine ordered for the SR99 project. From the floor Martin Herrenknecht asked: “Why did you choose an EPBM? I would have selected a slurry system. I wish you good luck but you will have problems.” He added in reference to anticipated boulders in the glacial deposits of Seattle: "You would be much better cutting the boulders. Settlements will be a problem and how will you get in under 5.6 bar pressure? With this high water pressure I am quite afraid. I think that finally you will end up with a slurry machine on a screw conveyor." In response, and after presenting his paper to the session, Alejandro Sanz of STP JV partner Dragados of Spain, said: "We have analysed the situation carefully and for us an EPBM is the choice. In this area there has been a problem with a slurry TBM getting stuck."
Futher feedback comments received including an ‘I told you so’ warning by Dr Tom Williams of the USA who refers to the SR99 TBM’s encounter with the steel borehole casing and questioned the suspected operation of the mega 17.5m diameter EPBM in relation to torque. In his full comment published on our Feedback page, Williams makes clear his preference for open-face tunnel excavation and criticizes plans by engineers in Los Angeles to use four TBMs of up to 60ft (18m) to excavate the missing SR-710 highway link through the hills between Pasadena and Riverside.
Other off the record comments also question the accuracy and scope of the site investigation programs by the client and ahead of tunnel excavation start, referring in particular to the encounter with the steel borehole casing. Others have highlighted the issue of high cutterhead torque commenting that clogging of material in the excavation chamber of such a large diameter EPBM would increase torque significantly. There have also been comments about wear of the cutterhead tools being excessive and unable to cut material in the face as well as suggestions about the effectiveness of the conditioning system and its operation on the huge machine.
All are comments from professional engineers with personal experience and case studies available to back their suggestions and opinions. All are relevant and worthy of being included in the overall discussions about the progress of one of the industry’s largest, most important and most high profile projects of current times. Comments and feedback is welcomed by TunnelTalk on all is published content and will be reviewed, edited as required, and published.