Standing Guard at the Pentagon
Precast concrete retaining/security
walls epitomize - and enhance - our nation's
strength.
By Leslie Lichtenberg
After a search for a team
to design and build a $60 million Remote Delivery
Facility at the Pentagon’s, the U.S. Department
of Defense turned to Hensel Phelps Construction
Co. in Chantilly, Va. Hensel Phelps, who signed
on as the general contractor for the project,
subcontracted precast concrete manufacturer
Smith-Midland Corp. in Midland, Va., to create
a retaining wall and security wall leading to
architecture.
“This was a design-build
project, which meant there were no existing
drawings or specifications,” said Ashley
Smith, vice president of Smith-Midland. “We
had to come up with the design and the pattern
for the precast form as well as develop a system
to brace against the dirt behind the retaining
wall.”
Day-to-day operations of the
Pentagon Remote Delivery facility continued
throughout the construction process, adding
to the challenge of the fast-track project,
which was one of the Pentagon’s first
design-build endeavors in recent years. Also,
with a construction area only 20 feet wide along
the face of one wall, careful measures were
taken to unload delivery trucks daily in order
to prevent the accumulation of extra equipment
on the jobsite. “The work area was small
and extremely tight, which required us to carefully
coordinate all construction activity with other
trades,” explained Smith. Teamwork made
the project successful and ultimately produced
an outstanding product on time and within budget.
The Remote Delivery Facility
is a 250,000-square-foot below-grade structure
that serves as a temporary holding area for
supplies and equipment delivered to the Pentagon.
It also provides space for the Pentagon’s
maintenance facilities and even contains a post
office. Trucks pull in below the building and,
because of tight security measures, have limited
ingress and egress to and from the area.
The two key components of
the project comprised 12,000 square feet of
retaining wall panels and 936 linear feet of
parkway guard wall. HDR Architecture of Alexandria,
Va., aimed to integrate the design of the two
walls into the site without compromising the
historical significance of the Pentagon. To
meet this objective, they took advantage of
the natural sloping grade of the site to screen
the activity surrounding the building.
The stone knee wall was designed
as a perimeter wall to provide a visual and
physical barrier to traffic on State Highway
110, which runs adjacent to the Pentagon. Special
design features included a wrought iron fence
enclosure to complement other structures found
throughout the Pentagon Reservation.
The retaining wall consisted
of steel I-beams embedded into the ground every
8 feet on center with wooden lagging panels
to support the ground behind the wall. Precast
concrete facing panels measuring 8 feet wide,
8 feet to 14 feet tall and 6 inches thick were
installed on the face of the steel beams, and
a 2-foot-wide coping was attached to the top
of the wall to give the appearance of a solid
stone façade.
“Precast concrete proved
to be the best product for the two applications
on this job – a retaining wall and a highway
crash barrier,” said Kevin Conan, senior
estimator for Hensel Phelps Construction.
According to the general contractor,
the use of alternative building materials would
have required additional excavation as well
as the installation of a temporary retaining
system prior to building the wall itself. The
decision to build the retaining wall and the
knee wall crash barrier with precast concrete
eliminated the need for multiple labor trades
and therefore saved money.
The parkway guard wall panels
were 2 feet thick and 30 inches tall, with each
section measuring 10 feet long. The guard walls
were constructed with a 1-foot-tall, 4-inch-wide,
built-in footer to help keep the panels aligned.
HDR Architecture took great
care in designing the project. Stone bridge
abutments and architectural elements along the
parkway provided the prototype for the exterior
panel design on both the retaining wall and
guard wall. A patterned ashlar formliner gave
the face of the panels the appearance of hand-cut,
hand-laid stone. An architectural facing mix
was used that incorporated a blend of gray and
white cement with white limestone coarse aggregate,
white fine aggregate and black accent chips.
The precaster also developed a sandblasted finish
that revealed the aggregate on the “stone”
surface of the panel to match the other elements
in the area.
“A hand-laid stone wall
would generally be 20 percent to 30 percent
more expensive, but since this was a fast-track
project, we saved 50 percent on time and installation,”
said Smith.
The integration of these design
concepts and materials were essential to maintaining
the integrity of a structure that is part of
an important national landmark. Everyone on
the team considered it a major victory that
such goals were accomplished without adding
to the cost of the project.
The $1.7 million retaining
wall and security wall project was completed
in 2001. It has exceeded expectations for providing
strength, permanence, weather resistance and
all the other qualities that make precast concrete
an ideal material for retaining and guard walls.
Despite security issues, space constraints and
tight turnaround expectations, the retaining/security
wall project is a shining example of the benefits
of using precast concrete; namely, overall economy
and speed of installation.
Project Profile
Project
Name: Remote
Delivery Facility
Owner:
U.S. Department
of Defense
Architect:
HDR Architecture
Inc., Alexandria, Va.
Contractor:
Hensel Phelps Construction
Co., Chantilly, Va.
Precast Manufacturer
and Engineer:
Smith-Midland
Corp., Midland, Va.
