to mark the height restrictions. To speed soil removal, the
company had custom-designed, small excavation bins
imported from Europe that could hold more than a typical
clamshell (four cubic yards vs. two cubic yards, doubling the
excavation production).
With worker safety a primary concern, the four new loaders
Goldin & Stafford ultimately purchased included scrubbers to
clean the exhaust and keep the work environment safe from
equipment exhaust fumes. Hensel Phelps also set up large
fans that were designed by a mine ventilation engineer and a
flexible temporary ductwork system to produce constant fresh
air and ensure consistent air circulation in the confined space.
The fans also included silencers to substantially reduce the
noise they generated while running constantly and providing
330,000 cfm of air to the below-grade spaces.
Once excavators dug down to the floor levels, concrete
contractor Baker DC, LLC installed a three-inchmud slab to act as
aworking surface for installationof the requiredelementswithin
the two-foot-thick below-grade floor slabs. Steel subcontractor
Canam/LPR then installed two-inch-thick steel plates with
nine-inch-long nelson studs around all slab openings, such as
elevator, stair and mechanical shafts. The plates were welded
together after their size and orientationwere confirmed tomeet
the structural design specifications. Canam/LPR also installed
wide flange beams between many columns.
After all the structural steel was installed, Baker DC installed
two layers of reinforcing steel (#8 rebar in both directions,
spaced 1 foot apart). Additional reinforcing steel elements
were installed around the embedded beams and at the steel
plate locations. Finally, Baker DC placed the 24-inch-thick
concrete structural slabs.
“Our challengewas placing over 39,000 cubic yards of concrete
and installing approximately 4,000 tons of reinforcing steel
over an 825,000 square foot area using the top-down method,”
said Richard Williams, Baker DC’s senior project manager.
“During the winter we were faced with cold weather and a
lack of direct sunlight. This retarded the concrete set time even
with added accelerators. Crews often worked 14 to 16 hours to
make sure the job was completed to the strict specifications
for floor flatness and levelness.
“We were also challenged with equipment as conventional
gas-powered equipment was prohibited. We used all-electric
equipment or placed scrubbers on the diesel equipment that
was permitted as air quality was constantly monitored for
optimal working conditions,” Williams said. “Each co-worker
was assigned an air monitor and oxygen tanks and we
implemented the buddy system where a minimum of two
co-workers would be assigned to tasks so they could keep an
eye on each other.”
For Cleveland Construction Inc. the hardest part of working
below grade was getting the material into the building. The
company installed all of the below-grade drywall plus the
drywall for the atrium facade, which extends from the hotel
lobby all the way up to the skylight. “We coordinated between
Hensel Phelps and our supplier to boom it down by crane,”
said Dave Huff, general manager. “We brought our suppliers
in between 4:00 and 5:00 a.m. to beat traffic and to get our
materials in before the day started.”
The company’s crews worked on the framing and installation
of mold-resistant drywall for the spaces around the
mechanical equipment even as the floors below were still
being excavated. “We were framing away and the dirt was
flying right past us,” said Huff.
Keeping the complicated project on schedule required close
and constant coordination between Hensel Phelps and its
subcontractors, plus long hours and many double shifts for
their workers.
BALANCING ACT
To maintain the project timeline Hensel Phelps also needed to
build above and belowground simultaneously. That presented
different challenges.
With 1,175 guest rooms and 49 suites, the upscale Marriott Marquis serves
as the headquarters hotel for the Walter E. Washington Convention Center.
10 Building Washington
