34 Pile Buck Magazine | Vol.30 No.3 2014 | pilebuck.com

PILE BUCK SPOTLIGHT

Every day about 134,000 vehicles cross the Tappan Zee Bridge trav-elling over the Hudson River in

the New York Metropolitan Area. Since the 1980s, the bridge has been in notable decline and undisputedly would be costly to repair.

The Final Environmental Impact Statement foresees that maintaining the current bridge would cost $1.3 bil-lion over the next decade.

To address this problem, as well as other shortcomings, the decision was made by the New York State Thruway Au-thority to replace the bridge rather than expend funds

to mitigate the deficiencies identified at the Tappan Zee Bridge. The new design is being constructed to be safer, improve traffic and may one day support a rail line.

On March 9, 2012, the New York State Thruway Authority put out a Request for Proposal to design and construct a new bridge

under the Design-Build delivery method. The new bridge is referred to as the “New NY Bridge.”

A Blue Ribbon Selection Committee was created to evaluate the proposals. The criteria for selecting the win-ning bid included judging the design, management, and ex-perience of the participants,

TAPPAN ZEE CONSTRUCTORS’ COST-SAVING PROPOSAL FOR NEW NY BRIDGE PROJECT

By Mark Georgian

pilebuck.com | Vol.30 No.3 2014 | Pile Buck Magazine 35

as well as, cost. The commit-tee was instructed to evaluate the plans with approximately equal weight given to techni-cal merit and cost.

Cost played a role in de-termining the winning bid, therefore, it was crucial for the bids to have an efficient design in terms of both ma-terial and construction.

The winning proposal came from Tappan Zee Constructors, LLC. (TZC), a consortium of design, engineering and construc-tion firms, including Fluor Corporation, American Bridge Company, Granite Construction Northeast, Inc, and Traylor Bros., along with key design firms HDR, Inc., Buckland & Taylor, Ltd., URS, and GZA GeoEn-vironmental, Inc. HDR is

the lead designer and GZA is handling the foundation design and quality control.

The new bridge contract is $3.142 billion. This win-ning proposal used an ag-gressive foundation design that kept the cost of the foundation in check.

According to Robert J. Pal-ermo, P.E., senior vice presi-dent at GZA, “One of the cost drivers here was certainly the foundation design”. “The structural design by HDR and GZA’s foundation design allowed us to go with 350-foot spans. This resulted in considerable cost savings [by reducing the number and length of piles needed],” ac-cording to Walter Reichert, TZC’s project manager. In addition, the project took an aggressive approach on

the pile design, resulting in savings from reducing the length and wall thickness of the piles themselves.

For this design to work, the piles need to be able to support the long spans. Palermo stated, “GZA felt confident that we could get the [needed] capacity on the piles in order to design it.”

Palermo summarized, “The longer spans and ag-gressive pile design allowed TZC to come in quite a bit lower in terms of bid price on this job.” HDR and GZA worked closely with TZC during the proposal phase of the project to provide a very efficient design. Ac-cording to HDRs design director, Jeffrey Han, “the collaboration promoted by the Design-Build process

resulted in our innovative approach to the foundation design and ultimate success of the pursuit”.

Even with the long spans, the bridge still has a total of 42 piers and about 1,100 piles.

These piers are support-ed by three different sizes of piles. The largest piles are 72-inch-diameter open ended pipe piles bearing on bedrock or glacial till and support the foundations for the main spans. The load on each main span pile is about 7100 kips.

The majority of the piers supporting the approaches use 48-inch diameter open ended pipe piles with capaci-ties ranging from 3800 kips to 5400 kips. About half of these piles are end bear-ing and the remainder are

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36 Pile Buck Magazine | Vol.30 No.3 2014 | pilebuck.com

PILE BUCK SPOTLIGHT

friction piles that derive their support in the thick (up to 500 feet) varved silt and clay deposit. The friction piles used in the project are up to 332 feet below the mud line into varved clay. The capacity of these piles ranges from 3,800 kips to 4,200 kips.

Both the 48- and 72-inch-diameter piles utilize 1-inch thick walls.

Smaller, 36-inch diameter piles with 1.25-inch thick walls were used as founda-tion support of the new bridge piers along the river bank. Palermo explained, “We saved a significant amount of money on the wall thickness of the piles.” Extensive analyses were conducted to select a ham-mer that could drive the piles to the depths and capacities

required, without overstress-ing the thin-wall pipe.

The team was innovative in their approach in some of the environmentally sensitive portions of the project. Work in the shallow areas required dredging, adversely affecting the spe-cies in the area. The existing environmental permitting for the project allowed for a 1.8 million yard dredging prism, but the plan proposed by TZC and HDR required only 0.95 million yard prism, a 47% reduction.

Rather than perform dredging along the river banks to provide adequate draft for barges and tugs to install foundation piles, a trestle was built so that crawler cranes could be used to install the 36-inch piles in

the shallow areas. The trestle allowed for a reduction in dredging at the end of the new bridge. The smaller piles allowed TZC to use a lighter crawler crane and smaller hammer to limit the weight on the temporary trestle. This improvement was one of the “Aspects of Superior Solution” cited in the Blue Ribbon Committee Report.

Another consideration for the design and installation of pile foundations bearing on bedrock was the steep incline of the bedrock. This poses problems for pile driving because the piles can glance off the steep face. In this event, the piles are likely to be damaged.

Palermo stated this is a problem because, “If you look up the cost of each pile,

they are not cheap.” The project team engaged Bengt Fellenius, Dr.Tech., P.Eng., Mike Holloway, Ph.D., P.Eng., and Dan Brown, Ph.D., P.Eng. to assist in developing an effective approach to address these conditions.

Palermo summarized the resulting strategy this way, “Rather than driving the piles as hard and quickly as possible, install the pile to the top of rock or glacial till using as little energy as prac-tical to keep the pile moving. When the pile encounters hard driving, we hit it 80 or 100 times with low energy to “chisel” the piles into the bedrock. Once we feel like we have it firmly seated, we hit it with a limited number of blows at high energy just to demonstrate capacity.”

38 Pile Buck Magazine | Vol.30 No.3 2014 | pilebuck.com

PILE BUCK SPOTLIGHT

Both dynamic and static testing of the piles is being conducted. For the static tests, a water-filled barge and a crane counter weight were used to apply a load of just over 7 million pounds to a reaction frame. Up to five, 9000-ton jacks were used to apply the load in up to 50 feet of water.

As a supplement to the conventional pile load test-ing setup, an automated AMTS located on the barge was used to shoot targets on the reference piles, the reaction piles, the test piles and also on the existing bridge. The readings were automatically electroni-cally sent to people on- and off-site. Automating this process ensured that up-to-date data was shared efficiently, also realizing some savings.

Another way that TZC was able to keep cost down was proposing the use of an enormous crane called the “Left Coast Lifter.” It has a 328-foot boom and is capable of lifting 1,900 tons, which

is 12-times the weight of the Statue of Liberty.

This crane will be used to demolish the old Tappan Zee Bridge as well as to erect massive precast bridge components to save time and reduce construction costs. It is able to lift large sections of the bridge and place them on a barge to be destructed off-site rather than taking down the bridge in smaller pieces.

The crane was recently used on the San Francisco Bay Bridge project where it was named the “Left Coast Lifter” and was the largest crane ever used on the West Coast.

The project has been un-derway for almost one year. The construction test pile

program began in July, 2013 with production pile driving beginning in October, 2013. The bridge will open for traf-fic in stages. The first span of the new bridge is scheduled to open in 2016, at which point all traffic will routed to the new bridge and the old bridge demolished. The east bound bridge should be completed in 2017 and the project physically completed April, 2018. The bridge has a 100-year service life.

When construction is completed, the bridge will feature several improve-ments. Shoulders and emergency access are being added. The reduced incline of the new bridge is

anticipated to improve flow and reduce the number of accidents. Additionally, there will be a shared-use path for pedestrians and bicycles.

Although not completed within this contract, the bridge was designed and constructed to be mass-tran-sit-ready. The new bridge will accommodate bus rapid transit, light rail or com-muter rail construction with respective funding obtained in the future.

More about the pile driving process for this project will be presented at the “SuperPile ’14 piling design and construction conference” in Cambridge MA, June 18-20.

COST PLAYED A ROLE IN DETERMINING THE WINNING BID, THEREFORE, IT WAS CRUCIAL FOR THE BIDS TO HAVE AN EFFICIENT DESIGN IN TERMS OF BOTH MATERIAL AND CONSTRUCTION.