that needed to be finalized prior to bidding. A range of engineering
calculations were performed to evaluate potential variability in
pile length for bidding purposes.
The RFP required load testing of sacrificial piles to confirm pile
capacity before the designs were finalized. While not necessarily
new or innovative in 2018–2019, two sacrificial piles were statnamically
load tested, a very expensive dynamic load testing technique
used for piles whose design (and test) loads cannot practically be
confirmed with conventional static load testing. Test loads of up to
3,500 kips per pile were needed.
A third obstacle was the construction of the eastern abutment
on land, which was designed in close proximity to an aged, 108-
inch diameter sanitary sewer line owned by DC Water, which was
very concerned about rupturing the line during pile driving.
Innovation
The project provisions stipulated very low allowable vibrations
imparted on the 108-inch sanitary line and clearly outlined liability
(to the design-build team) if the line was damaged as a result of pile
driving (or other construction activities). The sanitary line could
not be taken offline or rerouted temporarily during construction,
nor could the line be surveyed for structural condition prior to the
start of construction. The designers specified a combination of predrilling
and permanent casing to be used for some piles nearest the
sanitary line to lower induced vibrations. This resulted in variable
pile lengths in this substructure. The loads on each of the 32 piles
in the eastern substructure (laterally and vertically) were evaluated
by the designers and unique embedment lengths were determined
for each pile. Ultimately, the piles were driven for the eastern abutment
in very close proximity to the sanitary line without incident.
The open-end diesel hammer used for this project is very large and
was uniquely built for this project.
Environmental requirements
The District Department of the Environment (DDOE) maintained
an active role in the project from the early design phase to the
current date. The soils on the shore and bottom of the Anacostia
River are environmentally contaminated, and DDOE representatives
have been on site to confirm adherence to the environmental
regulations required for the project. By changing the foundation
type from cofferdam/drilled shaft to driven piles, the amount of
excavated soil (including that excavated from the river bottom)
was significantly reduced. Disturbance of the soils at the bottom
of the river was lessened by using driven piles versus cofferdams.
Award-worthy project
It is not often that the foundation costs of a large design-build
transportation project influence the overall costs or award of a
project. For this project, a reduced foundation footprint, together
with schedule improvements by switching to driven piles (i.e.,
not having to build cofferdams to build the bridge foundations)
proved to be a key aspect of the overall cost and design of the
project. Additionally, there were significant technical challenges
to overcome to make the project ultimately successful, such as
negotiating the driving/vibration thresholds that nearly adversely
impacted the east abutment construction. t
ASSOCIATE/ENGINEERING AFFILIATE CATEGORY
The open-end diesel hammer used for this project is very large and was
uniquely built for this project
Large diameter open-end steel pipe piles were used as deep
foundations to support the new bridge
88 | ISSUE 3 2020 www.piledrivers.org
/www.piledrivers.org
