TECHNICAL APPROACH ON BID PREPARATION TO SUCCEED ON THE ALASKAN WAY PROJECT

摘要

The WSDOT has decided to replace the old Alaskan Way Viaduct on the SR99 forrna single bore tunnel able to allocate two lanes on each direction. In accordance withrnthe ground conditions existing on Seattle a pressurized TBM is the right choice. But, thernrequired 57.4' on excavation diameter goes by far, beyond the existing TBM’s and willrnrequire the application of the newest technologies on its development.rnTo succeed on this bid a careful and documented technical approach was made,rnevaluating first the two options between slurry and EPB to excavate the tunnel, followedrnby the selection of the most effective and proved systems and devices, sometimesrnduplicated, in order to build the perfect machine for the biggest TBM tunnel everrnbuilt, till now.rnNot only the TBM, but also the impact of the new urban tunnel on the surroundingsrnmust be deeply considered during the bid stage in order to estimate the cost and schedulernof the ground treatments required to minimize the volume loss and consequently tornprogress with the excavation in the safest way for all the parties (see Figure 1).