Integration of Operations and Underground Construction: Sound ...

Operational considerations and Neighborhood stakeholder concerns at the PSST
Early in the design of the connection design it was made clear to us that disruption of the Sound Transit and King
County Metro operations within the PSST had to be held to a minimum. After some reflection on all of the
construction activity that could not be avoided within the PSST and the risks this posed to ongoing transit operations
the concept of “demising walls” was developed. The “demising walls” are fixed bulkheads fitted out with roller and
personnel access doors constructed between 15 and 20 m (50 and 65 feet) from the PSST headwall in order to create
a construction exclusion work zone. These bulkheads have been designed to prevent the communication of dust and
noise from the zone, control personnel access into the active transit operations area, and maintain the integrity of the
existing FLS (Fire Life Safety) ventilation. Installation of the bulkheads could not avoid impacts to the PSST.
Relocation of the light rail “bumper posts” reduces the available storage length for light rail vehicles by
approximately 60 feet and restricts Sound Transit to two-car travel. However, the advantages of the bulkheads
outweighs this temporary inconvenience to operations and Sound Transit will not need a three-car service until the
completion of University Link in 2016. Once the bulkheads have been installed they will remain in place until all
systems and other finishing works have been carried so that the seamless integration of the U-Link with the PSST
can be completed.
To address the concerns that site neighbors and other stakeholders would have of further construction being carried
out that would disrupt traffic on Pine St. the design team came up with a feasible approach that would ensure that for
the most part construction activities would take place within the site boundaries, only stepping outside into the side
walk areas for very specific operations such as the angled jet-grouting below Pine St as shown in Figure 3.
Figure 3. Jet grouting below Pine St.
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