July/August 2021 - 19

Utility Support Structure (TRUSS),
consisted of a 154 ft (47 m) long steel box
truss superstructure supported by
reinforced concrete abutments. The
location selected for the temporary
structure placed the abutments within 5
to 15 ft (1.5 to 5 m) of a 65 ft (20 m) deep
portion of the excavation. Also, the
structure foundations were located atop
existing subsurface utilities that had to
remain in-service until rerouted, which
severely constrained the abutment
foundations.
With limestone nearly at grade on
the east abutment, a spread footing with
a void form over underlying utilities was
utilized. The west abutment required
short-drilled shafts into the limestone to
address conflicts with an adjacent
retaining wall and a proposed temporary
gravity stormwater line (which was approximately 10 ft
[3 m] below ground surface and would be installed while the
TRUSS was in service). The design also had to account for
lateral forces from the abutments being transferred into the
retention system, with rock anchors installed within the
abutments to restrain these loads.
BIM Modeling
The project required that all permanent structures be
designed using BIM (Revit-based) platforms. The retention
system was also modeled in Revit, with live models shared
via an Egnyte server. To ensure the entire TRUSS system
coordinated with the retention system components, both the
superstructure and concrete abutments were included
within the overall excavation BIM modeling. Every anchor for
the retention system (over 3,000 total) was uniquely
identified with a tag indicating phase in which it was used,
location, length, etc. This automatically prevented duplicate
anchor tags during design and facilitated communications
between the project team during construction. The Revit
model further provided an automated means to develop
anchor schedules and manage the procurement of required
materials - such as the approximately 90,000 lft (27.4 km) of
anchor tendons required. Including the excavation support
system in the BIM also facilitated coordination with the
ongoing permanent civil and structural design development.
Anchor elements included a tolerance zone to determine
potential conflicts with adjacent underground structures and
utilities (existing and proposed). Several iterations of clash
detection and conflict resolution occurred as the design
progressed to reconcile the retention system with the
permanent structure and utility improvements. The 3D
model also facilitated interleaving the retention system
anchors at re-entrant corners to preclude conflicts. As a result
of this coordination, the project experienced minimal impacts
from underground conflicts during construction (one minor
design modification due to a utility as-built location error that
affected four anchors).
TRUSS superstructure and abutments
Isometric of Revit 3D
coordination model, with
1601 Congress in orange
Actual fault plane location and orientation observed during Phase 1A
DEEP FOUNDATIONS * JULY/AUG 2021 * 19
July/August 2021

Table of Contents for the Digital Edition of July/August 2021
