November/December 2021 - 19

The tunnel itself, which enters the pitch at a depth of 22 ft
(6.7 m), is 90 ft (27.4 m) long by 20 ft (21.3 m) wide by 20 ft
(21.3 m) high. Its incorporation into the secant wall required
extensive planning, coupled with skill and finesse on the part
of the drill rig operator. The entrance retaining walls, which
are 90 ft (27.4 m) long on the east side and 68 ft (20.7 m) on the
west side, required 40 soldier piles, 36 in (91.4 cm) in
diameter. They were placed 7 ft to 8 ft (2.13 m to 2.43 m) on
center and drilled down to glacial till at an elevation of 675 ft
(206 m). The design also incorporated 36.6 in (15.2 cm) posttensioned
tieback anchors, which were drilled through the
steel beams to depths of 50 ft (15.24 m) to 60 ft (18.3 m). The
anchor down angle was between 40 and 45 degrees. The
horizontal skew angle was primarily at 0 degrees, but ranged
from -16 degrees to +17 degrees. Anchor lengths varied
between 49 ft (15 m) and 58 ft (17.7 m), and design loads, from
160 kips to 220 kips.
Due to the U-shaped wall that wraps around to meet the
secant pile cutoff wall on both sides, the tieback anchors
ultimately created a spider web effect, layering on top of and
crossing over one another. Per standard procedure, for this final
phase of the project to be successful, all drilling was mapped
out via AutoCAD and building information modeling. Special
attention was required of operators in the field, who had to
avoid ACPs that were already in place and other tieback
anchors that were skewed at intersecting angles, while
attempting to anchor the new tieback at a 5-degree angle.
Dan Brown and Associates cultivated an individual list of
risks and obstructions should the operator drill too close or
into another structure. Along with that document, there were
3D models of all tiebacks and pilings in place. Despite a few
close calls of coming within inches of an ACP, operators were
able to install tiebacks without any setbacks.
Conclusion
The location of the Columbus Crew Stadium adjacent to a river
in a 100-year flood plain and high groundwater levels
challenged the design and construction team to develop a
solution that would keep the playing field - which was below
the floodplain and 22 ft (6.7 m) below the concourse level - dry.
Anchored soldier pile wall for pitch access tunnel
The design assist subcontractor proposed a secant pile
wall for the cutoff wall design that would encircle the Ohio
stadium. Other proposals favored a slurry wall solution,
which Goettle cited as being problematic during excavation
and pile drilling due to cobbles and boulders in the substrate.
In addition to surrounding the stadium perimeter as a
cutoff wall, the 2,300 lft (701 m) secant pile wall also acts as
the back form of the stadium foundation walls and retains the
overburden soils for the pitch level grading. The wall consists
of interlocking primary and secondary piles, with steel beam
reinforcement at the alternating piles. The unreinforced
primary piles used low-strength ACP grout, whereas the
reinforced secondary piles were finished with higherstrength
grout, with 27,000 cu yd (20,643 cu m) poured. During
the 5-month installation period, the subcontractor used
Bauer BG40 and BG45 drilling rigs to perform CFA drilling
methods, accommodate pile depths and conquer obstructions
posed by cobbles and boulders.
For Goettle's second contract to construct the stadium's
foundation, large diameter ACPs were required. Running
concurrent with the secant pile wall, the subcontractor added
another rig to drill 506 piles ranging in depth from 50 ft to 75 ft
(15.2 m to 22.8 m).
Posing the biggest and most interesting construction
Tunnel cutoff wall plan
challenge was the pitch access tunnel, which runs from grade
to the playing field (pitch) and is 90 ft (27.4 m) long and 20 ft
(21.3 m) wide and high. Its incorporation into the secant wall
required extensive planning, coupled with skill and finesse
DEEP FOUNDATIONS * NOV/DEC 2021 * 19
November/December 2021

Table of Contents for the Digital Edition of November/December 2021
