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Port Infrastructure:
Marine Commerce Terminal in New Bedford, MA
Susan Nilson, P.E.
1
, John DeRugeris, P.E.
2
, Eric M. Hines, Ph.D, P.E.
3
,
Jay Borkland
4
, David Carchedi, Ph.D., P.E.
5
, Diane Y. Baxter, Ph.D., P.E.
6
1
CLE Engineering, Inc. 15 Creek Rd., Marion, MA 02738 PH(508) 748-0937;
email: SNilson@CLEengineering.com
2
CLE Engineering, Inc. 15 Creek Rd., Marion, MA 02738 PH(508) 748-0937;
email: JDeRugeris@CLEengineering.com
3
LeMessurier, 1380 Soldiers Field Road, Boston, MA 02135 PH (617)-868-1200 x440; email:
ehines@lemessurier.com; Tufts University, Professor of Practice
4
Apex Companies, LLC, 125 Broad Street, 5th Floor, Boston, MA 02110 PH(617) 728-0070; email:
jborkland@apexcos.com
5
GZA GeoEnvironmental, Inc., 530 Broadway, Providence, RI 02909
PH(401) 427-2706;email: david.carchedi@gza.com
6
GZA GeoEnvironmental, Inc., 530 Broadway, Providence, RI 02909
PH(401) 427-2742; email: diane.baxter@gza.com
ABSTRACT
The Marine Commerce Terminal (MCT) in New Bedford, MA is the first port
facility in the nation designed to support the construction, assembly and deployment
of offshore wind projects, as well as handle bulk, break-bulk, container shipping and
large specialty marine cargo. The MCT, which is located inside New Bedford Harbor
and protected by an USACE hurricane barrier, is in close proximity to offshore wind
planning areas along the East Coast that are under consideration for future
development. The MCT consists of a 1,200-linear-foot bulkhead system with deep-
water access and roughly 20 acres of port terminal space engineered to sustain mobile
crane and storage loads that rival the highest capacity ports in the nation. The most
demanding requirement of the terminal structure is supporting a ground pressure load
of 4,100 psf and the maximized reach of fully loaded cranes (500 tonnes at a distance
of 30 meters) to operate right up to the offshore edge of the platform and laterally for
the entire 1,000 foot length of the newly constructed facility.
As part of construction, the project included the dredging and removal of
approximately 280,000 cubic yards of contaminated sediment and the landside clean-
up of 18,000 tons of contaminated soil caused by industrial waste generated during
the 1930s and 1940s, a significant environmental benefit. Geotechnical challenges
included high bearing pressures, maximizing beneficial reuse of dredged materials,
and blasting near sensitive structures.
Construction of the MCT was completed in early 2015. This paper discusses
the port bulkhead facility design including the uniqueness of the site, dredging
considerations, structural design, and geotechnical engineering.
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INTRODUCTION
In 2009, the newly formed Massachusetts Clean Energy Center (MassCEC)
was tasked with facilitating plans to integrate offshore wind into the Massachusetts
energy landscape. One of MassCEC’s first tasks was to assess the infrastructure
needs that this new industry might have and determine where appropriate and
beneficial infrastructure upgrades could facilitate the development of the industry. A
critical component of the infrastructure required to support offshore wind is an
appropriately designed port facility, and as such, the work described herein was
commissioned by the MassCEC. Recognizing that the development of the first
offshore wind staging port in the U.S. would require the skills of a diverse team of
experts, the MassCEC constituted a Design Team to work on the new port facility
terminal. Apex Companies, LLC (Apex) was the engineer of record with a team
comprised of CLE Engineering, Inc. (CLE), which performed the structural design,
GZA GeoEnvironmental, Inc. (GZA) which performed the geotechnical engineering,
LeMessurier Consultants, which served as the Owner’s representative, Fuss and
O’Neil, for utility design and Aspera Associates to further support the development
of the Marine Commerce Terminal (MCT).
The first step in developing plans for a port facility terminal was to identify a
location. In 2010 MassCEC commissioned a study to identify the best Port within the
Commonwealth to support the developing Offshore Wind industry. After a thorough
evaluation of the State’s five major Ports, the State determined that the Port of New
Bedford had the most attributes that the Offshore Wind industry desired including but
not limited to: protected harbor, shipping channel depth, overhead clearance,
operational ability, exclusive use of port facility, berth length, shipping vessel water
depth, wharf and upland yard area, rail access, highway access, and proximity to
wind development areas (TetraTech EC, Inc., 2010). The Port of New Bedford was
identified as the best opportunity for the State to capitalize on the significant shipping
and fabrication activities that are associated with the installation of a Wind Farm.
Further, a MCT at this site would fully support global shipping operations that go
well beyond offshore wind.
The Port of New Bedford is on the south coast of Massachusetts, in close
proximity to wind development areas. The terminal is north of the US Army Corps
of Engineers’ Hurricane Barrier which provides protection from hurricane storm
surge. The site is directly south of South Terminal, an existing marine terminal
facility, and includes areas of upland, intertidal and subtidal land.
DESIGN CRITERIA FOR THE MARINE COMMERCE TERMINAL
The development of a MCT to support the offshore wind industry as well as
global shipping and specialty marine cargo represented a great challenge, not the least
of which was determining the correct specifications that would define the design
process.
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Figure 1. Overview of MCT Site (image from Google earth)
Bulkhead and Quayside Design Criteria. In consideration of the European ports as
well as criteria provided by potential users of the MCT, MassCEC developed design
parameters for the facility that ensured it would meet needs of current and future
wind farm installations. The Design Team learned from the knowledge that
European developers had gained during their decade long development of the
industry there. Direct correlations between European and U.S. applications, however,
were inconclusive as no two applications were identical. As a result of the MCT’s
unique context, MassCEC and the Design Team independently identified many of the
attributes that the facility would require for current and future offshore projects and
future industry trends.
Potential users of the facility identified the ability for super lift cranes to
transit laterally along the seaward face of the facility while carrying their loads as
advantageous for improved efficiency of operations. Therefore, the design criteria
included a structure capable of supporting a ground pressure load of 4,100 psf
(20 t/sq meter) as well as “super lift” crawler cranes capable of picking 500 tonnes at
a distance of 30 meters, and the more demanding feature of enabling their maximized
reach by allowing the fully loaded cranes to operate right up to the offshore edge of
the platform and laterally for the entire 1,000 foot length of the new facility.
Dredge Design Criteria. Apex Companies, LLC developed berth designs to
accommodate vessels likely to utilize the facility. The north end of the NBMCT was
designed for ships up to 500 feet in length, with drafts of up to -30 feet (9.14 meter)
MLLW. The ship berth is expandable up to 100 feet to the south, and up to 150 feet
New Bedford
Inner Harbor
Location of MCT
USACE Hurricane Barrier
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to the north. The southern 400 feet of the NBMCT is designed as a barge berth with a
draft of -14 feet (4.27 meter) MLLW.
A total of approximately 900,000 cubic yards (cy) of sediment was dredged to
complete the project design, including approach channels to the new marine facility
and dredging at the berth adjacent to the new quayside to accommodate the types of
vessels anticipated to be serviced by the Terminal. Of that, approximately 250,000 cy
of sediment was contaminated with levels of PCBs and heavy metals that could not
be reutilized within the project and would be extremely expensive to dispose of at a
conventional landfill. In order to create a viable and cost effective solution to the
contaminated sediment issue on the project, the project design incorporated the use of
a Confined Aquatic Disposal (CAD) Cell.
Geotechnical Criteria for Upland Facility. Gradations of acceptable dredged
material were developed for reuse at backfill behind and in the cofferdam cells.
Compaction of the materials was specified by vibrocompaction through the use of
driving a probe with a vibrating hammer through the placed dredged materials.
Various probe spacings were investigated and verified with the use of a drill rig and
standard SPT tests. In this way, dredged materials were re-used on site and were able
to meet the high crane bearing loads. Another aspect of the Upland Design included
removal of existing fill and recompaction of the fill to specified densities.
DESIGN OF BULKHEAD AND QUAYSIDE
There were several site related and conceptual design issues which needed to
be weighed as a whole in order to determine the most cost effective approach to the
project. The most significant site issue was the presence of extensive ledge rock
underlying the site, at a range of elevations, overlaid with a variable layer of
fragmented and highly fractured rock, and very dense glacial till populated with large
boulders. The most significant design criteria were the capacity requirements up to
the edge of the quayside and throughout the site to support heavy cranes.
Initial bulkhead and quayside concepts for the facility involved several
different design types: king-pile wall, tied back sheeting, filled concrete cell,
marginal wharf, and circular cofferdam cell wall. Each potential wall type was
evaluated in comparison to the existing conditions at the site coupled with the facility
design requirements determined during the concept design. The primary technical
factors influencing the bulkhead design were the load bearing requirements at the
quayside coupled with the presence of extensive rock and very dense till above the
target dredge depth. In order to alleviate high soil loads that would occur near the
face of the bulkhead, a shallow relieving platform was applied to all preliminary
designs.
A layout schematic of the final cofferdam wall alignment for the new facility
is shown in Figure 2. A cross-sectional diagram of the bulkhead and quayside design
of the facility resulting from the final design process is shown in Figure 3.
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Figure 2: Cellular Steel Cofferdams and Pile Supported Relieving Platform
Final Design. The final design of the bulkhead utilized 61 foot (18.6 meter) diameter
steel cells at 82.9 feet (25.27 meter) centers, and minor cells are a 15.4 foot
(4.7 meter) radius. Minor cells were constructed on both sides to allow pile driving
and other equipment to work from on top of the cells during construction; thus
providing schedule advantages for construction. The front third of the cell’s sheet
piles are driven to refusal, and the remainder of the sheet piles gradually stepped as
they progressed inshore. The sheet piles for the front half of the cells were Skyline
AS-500-12.7 sheets made of epoxy coated, 50 ksi A-690 corrosion resistant steel.
Costs were reduced by using lighter AS-500-9.5 uncoated sheet piles for the back half
of the cells.
Prior to installation of the cells, a layer ranging from two to seven feet of
geotechnically unsuitable soil was removed. Final backfill after cell installation was
predominantly select sandy soil from the dredging operations, which was vibro-
compacted to improve the density. The fill was topped off with a variable layer of
crushed stone, and topped with two feet of dense graded aggregate to provide a stable
walking surface for the cranes to operate on.
The cells were topped with a hybrid shallow relieving platform/ marginal
wharf, specifically designed to withstand the crane loads discussed earlier in this
paper. The design provided a pile supported overhang of approximately 13 feet (3.96
meter) from the seaward most face of the cells, and an additional 4’-9” (1.448 meter)
of stand-off distance was provided by the fender system. The overhang and fender
system was configured to allow enough room for the construction of a shaped rock /
soil slope from the toe of the sheet piles down to the berth dredge template. The
finished slope was then protected from scour by the installation of a 16 inch precast
concrete mattress. It can be seen from Figure 3 the design allowed for the unique
feature of allowing the cranes to work right up to the face of the bulkhead with a
lifting limit of 500 tonne, at a radius of 30 meters, which would allow for the loading
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and off-loading of the heaviest components of offshore turbines from ships and
support vessels. Figure 4 shows the site during cell construction.
Figure 3. Final design section of deeper draft bulkhead (dredging to -32, stepped
circular cells, overhanging pile supported platform and toe scour protection).
Overcoming Design and Site Challenges for Structure. One notable constructability
issue that the Design Team faced was the known presence of a considerable number
of boulders and fractured rock within the soil column. The flat sheets that make up
the cells have a very low section modulus individually, and it is only in their
interconnection with each other (in the formation of the circular cell) that they obtain
the strength of the whole. To obtain this unified strength the sheet piles must be
driven individually in a specific sequence to assure complete interlocking with each
adjoining sheet for the entire length. However, because of their relatively low
strength as individual sheet piles, they are prone to damage during the driving
process. They are particularly vulnerable to bending when they strike buried
boulders. There are few options available if or when this occurs, because if an
obstruction below one or more of the sheets does not allow the sheet to be driven to
design depth (i.e. it meets refusal above the design toe elevation), then the strength of
the entire cell is affected. To further complicate matters, one of the features unique to
driving circular sheet pile cells is that a sophisticated driving template must first be
put in place and carefully aligned, then leveled to maintain the circular shape and the
interconnected pattern of the overall pattern of all of the cells. Once this circular
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template is placed, then the entire circle of sheet piles must be “threaded” together
around the template to form the circle for what will become the cell wall.
Figure 4. Aerial View of Cell Construction in Progress
The problem that arises is that once the template is in place, and the ring of
sheets installed, and then driving is initiated, if an obstruction were encountered
during this phase of the driving, then it would become very costly and time
consuming to remove all or part of the cell wall as well as the template to allow the
removal of the obstruction. Knowing this, it became obvious to the Design Team
early on that because of the known presence of sizable rocks within the soil column, a
reliable and cost effective method would have to be devised to locate and remove as
many obstructions as possible in advance of the cell construction.
The Design Team specified a pile probe exploration program that was part of
the construction contract, which included probings to refusal at an interval of three
feet around the full perimeter of each cell. The selected contractor elected to utilize a
sizable vibratory hammer with a single H pile (HP14 x 117), clamped to the jaws
hanging vertically from a barge mounted crane. The crane had an RTK-GPS mounted
at the top of the boom for positioning, and a GPS navigation software program with a
heads-up display for the crane operator to align each probe. This exploration program
required an investment in over 1,800 probes, and yielded project savings that far
outweighed the cost of the probing program.
The procedure was relatively simple: the operator could see where each probe
was to be placed on the computer screen, and with the help of a crew member could
place the tip of the H-pile with relative precision (1’+/-), then vertically plumb the
pile in the X-Y directions. Once the pile was plumbed they would simply activate the
hammer and vibrate the pile to the design depth. An engineer recorded each location,
and observed the depth of any slowing of the probe during its decent or skewing of
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the probe that might indicate a physical obstruction. All of the data was then plotted
in an AutoCAD template of the project site, and the data from each obstruction
reviewed. A profile along the circumference of each cell was developed and a table
was generated to allow the contractor to go to the designated obstruction locations
and remove them. The probing program was considered very successful. It located a
considerable number of buried obstructions; it was roughly determined that at least
95% of the potentially problematic obstructions were found and removed in advance
of pile driving, which in itself resulted in viable savings in time and cost to all parties
involved.
Figure 5. Pile Probe Exploration for Obstructions in Progress
Interlock Strength and Testing. The use of circular steel cell cofferdams to support
ultimate and future working loads of the magnitude called for on this project pushes
the limits of currently available materials for construction of sheet pile cells. The
major issue that is encountered in the use of cells for heavily loaded sites is “Hoop
Tension”, which occurs in the cell interlocks, and vertical shear within the cell which
would be the result of extreme un-equal loading. The more important of the two
issues is the interlock tension, and there is an unusual performance issue with
interlocks in tension that must be considered when the design approaches the
advisable design limits of the material. The most common failure of a cell is the
pulling apart of an interlock, which normally occurs in the lowest third of the cell,
where soil pressure is at its highest. This failure is caused by the outer jaw of the
interlock which grips around its counterpart “knuckle” of the joining sheet (see
Figure 6 below) opening and thus releasing the adjoining sheet. It is also known from
experience that the junction-pile (where the cells are joined, or the “Y” connector) is
apparently the most highly loaded location, because it is the most common point of
failure. Both of these issues were carefully addressed in the design.
The first item addressed was the inherent weakness in the “Y” branch itself,
which for this project was specially reinforced using additional plates, installed by the
manufacturer, as shown in Figure 6. For the interlock issue, a more rigorous testing
program of the interlock “pull-apart” strength was specified by requiring laboratory
coupon testing of every sheet that would be used in the manufacture of the outboard
junction piles.
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Figure 6. Detail showing interconnecting knuckles of flat sheets, and the
reinforcement used to strengthen the junction pile “Y” connector
The increased testing protocol used for this project revealed another unusual
performance related issue with the sheet pile interlock. While all of the sheet piles
supplied by the manufacturer passed the design minimum “pull apart” load test by a
satisfactory margin, it was noted that the pull-apart strength is not directly correlated
to the strength of the metal used in the manufacture. The following are some general
statistics related to the testing:
Of 62 samples tested as of this writing, the yield strength of the steel itself
varied from a low of 5% above the minimum yield, to as high as 38% above
minimum yield.
Of these samples:
38% (24 Samples) ranged from 5% to 19% above minimum yield;
55% (34 samples) ranged from 20% to 29% above minimum yield;
7% (4 samples) were above 30% above minimum yield.
Interlock “pull-apart” yield strength ranged from 1% to 123% above the
minimum requirement; however these percentages were totally inter-dispersed among
all of the samples from the lowest to the highest yield, rather than among the samples
that tested as having the highest yield strength. For instance, of the 38% (24 samples)
that tested from 5% to 19% above minimum yield strength: 7 samples had pull-apart
yield from 1% to 9% above minimum; while the remainder were distributed from
10% to 113% above minimum with no direct correlation to the tested steel yield
strength.
Of the group of 55% (34 samples) that tested from 20% to 29% above
minimum yield strength; 4 samples had pull-apart yield from 3% to 9% above
minimum; while the remainder were distributed from 10% to 133% above minimum,
again with no direct correlation to the tested yield strength. The most surprising was
the 7% (4 samples) that were 30% or higher above minimum yield. All (100%) only
had pull-apart yield strength of 1% to 9% above the minimum (among the lowest of
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the test results); again demonstrating the lack of correlation between material yield
and interlock strength.
Our conclusion is that this unpredictability of interlock pull-apart strength
must be accounted for when designing heavily loaded steel cell cofferdams.
Therefore laboratory testing of not only minimum yield of the metal, but also
interlock “pull-apart” is extremely important. Specific additional reinforcing and
testing should be considered on critical or highly stressed components.
Overcoming Geotechnical Site Challenges. Geotechnical challenges included
designing the site for high crane bearing pressures and blasting near sensitive
structures. Many options to produce high bearing capacity were investigated
including ground improvement, deep foundations, excavation and replacement, and
reinforcement with geosynthetics. High groundwater, environmental concerns, and
schedule made many options impractical. Concerns that were investigated for the
geofabric included pull out, double seam installation procedures, and one-directional
strength for high strength geofabric. Concerns for the geogrid included proprietary
strength properties and proprietary software. It was found that the engineering
support for the geofabric and geogrid manufacturers evaluated different failure modes
but not all failure modes. It was determined that geosynthetic reinforcing did not have
a significant benefit over placing compacted fill without the reinforcing, and some
concerns could not be reconciled.
Rock blasting required to reach the dredge elevations was required in close proximity
to the USACE hurricane barrier, which is an earthen embankment constructed in the
1960’s. Seismic analyses were performed to predict the impact of vibrations from
blasting to address the Army Corp’s concerns over liquefaction or settlement of their
structure. Blast weight limits as a function of distance from the structure were
established for the project based on the analyses. A test blast program was conducted
to verify the assumed attenuation relationships. Real time monitoring of the
vibrations and pore pressures in the structure were conducted by the design team
using remote systems with no exceedances in threshold values.
REFERENCES
APEX Companies, LLC (2013) New Bedford Marine Commerce Terminal, New
Bedford, Massachusetts, Contract No. MACEC-FY13-001NB, Technical
Specifications
APEX Companies, LLC (2011) Design Analysis – New Bedford Marine Commerce
Terminal, Design Analysis Data Package and Value Engineering Memo
TetraTech EC, Inc., February 2010, “Port and Infrastructure Analysis for Offshore
Wind Energy Development”, Boston, MA
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