September/October 2023 - 16

Lift and suspension of historic roof over the project site (Photo: Anna Halstead, Mortenson)
Much of the realignment of the perimeter walls was at the
four snorkels at each corner of the structure. In order to
maintain the aesthetic qualities of the original arena design,
four remote headhouses were planned away from the original
structure to provide access and ventilation into the new
below grade space. These snorkels became quite complex
with large air chases, stairs, elevators and utility connections.
They were multilevel and included re-entrant corners rather
than being simply rectangular in configuration.
Two decisions on the perimeter wall system had to be
made early in the design process: how would the wall be
supported and what type of wall system
would be used? The engineering team
explored several ways to support the
wall without using continuous diaphragm
slabs. These included buttresses
using a type of T-panel system,
creating a ring beam using portions of
the floor plates around the open event
space, and tiebacks. While the tiebacks
may have seemed like the obvious solution, city ordinances
prohibited the installation of permanent tiebacks below
public streets. Therefore, while negotiations were underway
with the city for an exemption, all three options, possibly
16 * DEEP FOUNDATIONS * SEPT/OCT 2023
resulting in a hybrid system, were pushed forward. In the end,
the use of tiebacks was approved so long as a certain depth of
cover was maintained in the road right-of-way to allow for the
installation and maintenance of utilities. The plan was to
proceed with all the walls supported by permanent tiebacks.
As for what type of wall system would be best for the arena
project, the engineering team has had much success using
slurry walls in similar situations, and they were its first
option. Ground conditions in Seattle are well suited to the
construction of slurry walls, which are relatively robust and
allow for more widely spaced levels of support. In addition,
In order to maintain the aesthetic qualities of the
original arena design, four remote headhouses were
planned away from the original structure to provide
access and ventilation into the new below grade space.
slurry walls provide relatively good groundwater protection
and could be used to provide vertical support to new arena
facilities below grade. The slurry walls did, however, have
their drawbacks, such as installing the perimeter wall below

September/October 2023

Table of Contents for the Digital Edition of September/October 2023

TOC
September/October 2023 - Intro
September/October 2023 - 1
September/October 2023 - 2
September/October 2023 - TOC
September/October 2023 - 4
September/October 2023 - 5
September/October 2023 - 6
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