Bay Bridge Skyway: Sheet-Pile Cofferdam Shoring Techniques on the Eastern Span

Joe Lazzaretti
Jul 21
14 min read

Updated: Sep 2

The Bay Bridge Skyway Eastern Span project, completed between 2002 and 2013, replaced the original bridge after the 1989 Loma Prieta earthquake revealed structural vulnerabilities. This $6.5 billion project ($8.38 billion in 2023 dollars) prioritized seismic safety, ensuring the bridge could withstand earthquakes expected every 1,500 years while supporting over 270,000 vehicles daily. Key challenges included unstable bay mud, complex soil conditions, and harsh marine environments. Engineers used sheet-pile cofferdams to create dry workspaces, drive tubular piles at precise angles, and meet stringent seismic and construction standards. This approach allowed deep foundations to be built in challenging conditions, ensuring earthquake resilience and uninterrupted traffic flow.

Key Takeaways:

Foundation Innovation: Large-diameter tubular piles driven through soft mud into firm layers.
Seismic Design: Built to remain operational for emergency vehicles after major earthquakes.
Construction Techniques: Sheet-pile cofferdams enabled precise work in water depths up to 33 feet.
Environmental Compliance: Measures like silt curtains minimized impact on aquatic habitats.

This project showcases how tailored engineering techniques, like sheet-pile cofferdams, can meet seismic safety demands while addressing soil and marine challenges.

Project Requirements and Engineering Context

Eastern Span Structural Requirements

Replacing the Eastern Span demanded meticulous engineering to meet California's rigorous seismic standards. The 3.5-kilometer-long structure was designed to remain functional after major earthquakes, ensuring emergency vehicles could still use the bridge when needed[6]. The 1.2-mile Skyway section posed unique challenges, as its 452 pre-cast concrete segments required deep and stable foundations[4]. The complex soil conditions beneath San Francisco Bay ruled out the use of simple spread footings.

To address these challenges, engineers employed a combination of foundation techniques tailored to the site’s varied conditions. These included spread footings with hold-downs, steel and concrete piles anchored in drilled rock sockets, and steel tubular piles driven to remarkable depths[6]. In the most demanding areas, 160 rebar and concrete-filled steel piles - each with a diameter of 8.5 feet - were driven deep into stable soil layers. The foundation design followed performance-based criteria that set strict limits on footing displacement after earthquakes. This led to the use of both battered and vertical pile configurations, carefully selected to handle seismic forces and the site’s layered soil profile[6]. With seismic activity and variable soil conditions in play, the project required innovative solutions to ensure stability. These advanced foundation strategies paved the way for using cutting-edge shoring techniques in a challenging marine environment.

Role of Shoring and Cofferdams in Construction

The foundation challenges at the eastern end of the bridge called for the extensive use of sheet-pile cofferdam shoring. The Skyway spanned water depths ranging from 10 to 33 feet, with soft Young Bay Mud forming the topsoil layer[6]. Beneath this, a mix of soft mud and firmer aggregates required precise driving of large-diameter tubular piles at calculated angles to achieve the necessary bearing capacity.

Between 2002 and 2008, the Kiewit/FCI/Manson joint venture utilized sheet-pile cofferdams to create dry, controlled workspaces. These cofferdams allowed crews to pump out water and safely install the angled steel tubular piles through the soft mud and into the firm Alameda formation below. The absence of a dense Merritt sand layer at shallow depths - eroded by ancient Paleochannels - meant that battered pile groups were the only feasible foundation solution for the Skyway[7]. Additional challenges arose at the Oakland Mole approach, where poor soil conditions and steep ground relief further emphasized the need for temporary shoring systems[7]. The cofferdams ultimately enabled precise construction of concrete pads and pile caps, ensuring the foundation met the project’s stringent seismic performance standards. Steel sheet piling proved to be the ideal choice for this work, offering strength, availability, and ease of use in the demanding bay environment[5].

Sheet-Pile Cofferdam Shoring Methods and Application

Sheet-Pile Cofferdam Shoring Basics

Sheet-pile cofferdam shoring relies on interlocking steel sheets driven into the ground to create a watertight barrier. This barrier keeps water out, enabling construction work to take place in a dry environment even below the waterline [8]. This method played a critical role in the Bay Bridge Skyway project, where high groundwater levels, unstable soil, and a demanding marine setting required a dependable solution. Here's a closer look at how this system is installed and applied.

Installation Steps and Equipment

To install the sheet-pile cofferdam, vibratory hammers were used to drive the interlocking steel sheets through soft mud until they reached firm soil layers, forming the watertight barrier. Hydraulic bracing was then added to counteract the lateral pressure from both soil and water. Continuous pumping was employed to dewater the enclosed area [8][10]. The depth of the sheet piles depended on the soil conditions, with the goal of penetrating the soft layers to achieve sufficient bearing capacity. For the Bay Bridge project, excavation went as deep as 50 feet below the mud line in water approximately 20 feet deep. To ensure stability, multiple levels of lateral bracing were required [10]. These methods worked in conjunction with temporary support systems, which are discussed next.

Connection with Temporary Support Systems

Temporary support systems were essential in providing extra stability under the challenging marine conditions of the Bay Bridge project. These systems were designed using geotechnical data and included HP sections, welded steel tube piling, and multiple levels of lateral bracing. Together, they created a solid construction platform capable of withstanding significant loads. The project utilized 20 temporary cofferdams, 14 tower cranes, and 28 pile-driving templates to manage earth, equipment, and hydrostatic pressures up to 50 feet below the mud line [9][10].

The temporary steel sheeting was carefully tailored to match the size of the substructure and the findings of soil borings and geotechnical reports [9]. It was engineered to meet strict performance criteria, including a minimum nominal section modulus of 18.1 in³/ft for handling traffic loads. Additionally, the system was designed to limit deflection at the top of the sheet piles to no more than 2 inches [9]. These precise standards ensured the stability and safety of the temporary structures throughout the construction process.

Construction Challenges and Solutions

Deep Water and Soil Condition Management

Building the Bay Bridge Skyway Eastern Span came with its fair share of challenges, especially in the underwater environment. This section of the bridge stretches across water depths ranging from 10 to 33 feet, with a foundation resting on soft Young Bay Mud. These unstable conditions called for some creative engineering solutions [11].

To tackle the varying soil layers, engineers used a combination of spread footings, steel and concrete piles, and angled tubular piles driven as deep as 328 feet [11]. One particularly tricky hurdle was the dense Merritt sand layer, which appeared at inconsistent depths. To address this, battered pile groups were chosen to provide the necessary support for the skyway structure [7].

Sheet-pile cofferdams played a crucial role in stabilizing the construction site. These cofferdams enabled large-diameter tubular piles to penetrate through the soft mud and reach firmer layers below, creating dry and stable conditions for the work [1][7]. This method proved effective in overcoming the challenges posed by the marine environment.

The scale of the project added to its complexity. The Skyway spans 1.2 miles and consists of 452 pre-cast concrete segments supported by fourteen sets of piers, ranging in height from 45 to 115 feet. To ensure stability, piles were driven as deep as 300 feet [4].

Overcoming these soil and water challenges laid the groundwork for incorporating robust seismic safety measures.

Seismic Design and Lateral Stability

Given the Bay Area's high seismic activity, the bridge's design had to prioritize earthquake resistance. Engineers focused on creating a structure that could withstand seismic forces while allowing safe evacuation if needed [12].

The design adhered to IBC and ASCE 7 guidelines, which emphasize ductile systems capable of dissipating energy during seismic events. This approach ensured the bridge could flex without collapsing, providing crucial safety during an earthquake [12].

Several factors influenced the design, including site-specific ground motion, soil conditions, and the lateral force-resisting system. Temporary cofferdam structures were also carefully evaluated for their interaction with permanent bridge components during seismic activity [12].

Unlike regions like Florida, where wind loads dominate design considerations, the Bay Area's seismic risks dictated the need for additional reinforcement and specialized connection details. These measures extended to the temporary shoring systems, ensuring they could handle the earthquake loads [12].

Environmental Compliance and Regulations

Beyond engineering challenges, the project placed a strong emphasis on environmental responsibility. Measures like silt curtains and best management practices were implemented to protect water quality and aquatic habitats during cofferdam operations.

Silt curtains helped contain sediment and maintain water clarity in the bay. Additionally, erosion and sediment control practices were employed throughout the construction process to minimize environmental impact.

Before breaking ground, the team secured environmental permits and conducted thorough assessments to establish guidelines for reducing ecosystem disturbances. The cofferdam designs were tailored to meet both structural needs and environmental standards.

Even the demobilization phase received careful attention. Crews managed any remaining water and sediment within the cofferdams during removal to prevent pollution and ensure compliance with environmental regulations.

Continuous monitoring technology was used throughout the project, enabling quick detection and resolution of any environmental concerns. This proactive approach helped keep the project on track while adhering to strict environmental standards and staying within budget.

Equipment, Materials, and Construction Practices

Equipment and Materials List

The Bay Bridge Skyway Eastern Span project required a mix of heavy machinery, specialized concrete pumps, and durable materials to tackle the challenges of marine construction while meeting seismic safety and environmental guidelines. The $2.6 billion project relied on a carefully chosen array of tools and materials to achieve its ambitious goals [13].

Concrete Pumping Systems were at the heart of the operation. KFM, a joint venture formed by Kiewit Pacific, FCI Constructors Northern Division, and Manson Construction Company, utilized two primary concrete pumps: the S 58 SX and the KVM 39 X. These pumps managed the installation of over 185,000 cubic yards of concrete for the Skyway's substructure [13].

The S 58 SX boom pump, with its impressive 187-foot reach, handled about 75% of the pours. Grant Scott, KFM Concrete Superintendent, highlighted its importance:

"With the substructure alone we've got over 140,000 cubic yards of concrete going through these pumps. The 58-meter has that 187-foot boom that enables us to reach up and over for some of the larger pours at the column and pier table levels. We've utilized that long boom to its fullest extent on several occasions. To this point, it's completed about 75 percent of the pours." [13]

The KVM 39 X served as a secondary system, completing roughly 25% of the work. Scott explained its utility:

"The 39-meter comes in handy when maneuverability is important and setup needs to be executed quickly. We've utilized the pump for about a quarter of the concrete work, specifically on the piling and footing pours when we don't need that long boom reach." [13]

Heavy Construction Equipment included 14 tower cranes, which were strategically deployed to service alternating piers. A 150-foot pile-driving template ensured precise placement of sheet piles into the Bay floor [13].

Materials Selection emphasized durability and environmental responsibility. Steel sheet piles were favored for their strength and recyclability, while steel footings were pre-fabricated off-site and transported by barge to streamline the installation process [13].

The project utilized hot-rolled steel sheet piles due to their superior interlock seals, which effectively prevented water seepage. Though more expensive than cold-rolled options, their performance in a marine environment justified the cost [14].

Construction Materials included 452 precast concrete sections used to form the Skyway roadway. Rebar cages were installed inside the piles before concrete was poured, providing essential structural reinforcement [13].

Reliable equipment played a key role in the project's success. Scott emphasized this point:

"The first thing we asked ourselves was, 'Are these pumps going to get the job done?' We wouldn't stand for breakdowns or any type of maintenance problem that could set us back. The Schwings have been the center of this operation, and they have exceeded our expectations." [13]

The careful selection of equipment and materials laid a solid foundation for meeting the rigorous demands of U.S. infrastructure standards.

Construction Standards for U.S. Infrastructure

The project adhered to stringent U.S. construction standards and safety protocols, setting a high bar for large-scale infrastructure projects. These practices ensured worker safety and the structural integrity of the complex marine construction process.

Design Compliance and Approval Process mandated that all steel sheet piling designs meet the AASHTO Standard Specification for Highway Bridges and relevant state bridge design manuals. Temporary steel sheet piling and cofferdam designs underwent rigorous reviews to satisfy geotechnical and structural requirements. Construction teams were required to keep approved designs on-site, as per MIOSHA regulations [16][9].

Installation Standards and Tolerances were strictly enforced to ensure precision. Pile tops installed over water had a maximum allowable deviation of 3.94 inches, while land-based installations were limited to 2.95 inches. Verticality requirements were equally strict, with tolerances of 1.5% for piles over water and 1.0% for land installations, increasing to 2.0% in challenging conditions [15].

Quality Control Measures were tailored to each operation. ESC Steel LLC explained:

"ESC treats every sheet piling operation as a unique activity that depends ultimately on distinct parameters dictating the set of necessary quality control measures for sheet piles as individual material and as an integrated sheet pile wall or system." [15]

Construction teams used rigid guiding systems or frames to maintain verticality during sheet pile installation, regardless of the equipment or technique [15].

Safety and Structural Requirements included specific standards for temporary steel sheet piling near traffic areas. The minimum nominal section modulus was 18.1 in³/ft of wall, with deflection limits capped at 2 inches at the top of the sheet piling [16][9].

Environmental Compliance was a key focus throughout the project. All cofferdam operations adhered to environmental permit conditions, ensuring marine ecosystems were protected during construction [16][9].

Documentation and Inspection Protocols relied on standardized forms, such as MDOT form 1990, to monitor critical aspects of cofferdam installation and maintain quality control. The Michigan Department of Transportation's 2020 Standard Specifications for Construction prohibited practices like pulling up, cutting, and re-driving sheeting during temporary steel sheet piling operations to preserve structural integrity [16][9].

These rigorous standards and practices were instrumental in the successful completion of the Skyway portion, which alone represented the largest contract ever awarded by the State of California at $1.04 billion. The project's adherence to these guidelines directly impacted its seismic resilience and environmental safeguards [13].

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Contractor Insights and Project Takeaways

Drawing from the engineering and material challenges discussed earlier, contractors have shared valuable lessons that can guide future marine infrastructure projects.

Bay Bridge Skyway Project Lessons

The construction of the Bay Bridge Skyway Eastern Span provided a wealth of insights that continue to influence marine projects across the country. The sheer scale and complexity of the project offered opportunities for the construction industry to refine its methods and approaches.

One major challenge was managing deep excavations, which required innovative solutions. Cofferdams had to reach depths of up to 50 feet below the mud line, supported by multiple layers of lateral bracing. This highlighted the critical need for thorough geotechnical investigations before beginning cofferdam design.

The Kiewit-Flatiron-Manson joint venture tackled this challenge by using dewatered cofferdams to build all 21 bridge foundations. Their systematic approach ensured consistency and stability across the project, showcasing the importance of detailed pile-driving analyses to optimize installation and maintain the integrity of temporary structures. This approach supported the sheet-pile shoring techniques discussed earlier in the article [18].

Material selection and quality control also emerged as key focus areas. Early in the project, anchor rods failed due to hydrogen embrittlement, breaking at 70% of their intended tensile strength. This incident, which occurred in 2008, led to stricter material testing protocols and improved corrosion protection measures [17].

Salim Brahimi, President of IBECA Technologies and Chairman of the ASTM F16 Committee on Fasteners, explained the findings:

"The conclusion of this study stated that the cause of this failure was hydrogen embrittlement combined with the applied load exceeding the susceptibility of the rod material." [17]

Environmental planning also played a pivotal role. Protective measures were successfully implemented without disrupting the project schedule, demonstrating how environmental considerations can be seamlessly integrated into large-scale projects.

Ultimately, the Eastern Span's success proved that well-designed cofferdams can handle heavy traffic loads. Today, the bridge accommodates over 240,000 vehicles daily [17]. These takeaways emphasize the importance of selecting the right shoring technique, which is further discussed below.

Shoring Method Comparison

The Bay Bridge Skyway project provided valuable insights into the performance of various shoring techniques, offering guidance for future projects. Each method has unique benefits and drawbacks that need to be carefully evaluated based on site conditions and project goals.

Shoring Technique	Advantages	Limitations
Sheet-Pile Cofferdams	Excellent dewatering, reliable soil retention, proven marine performance	High initial equipment costs, requires specialized driving equipment
Cellular Cofferdams	Great stability for large projects, handles high water pressures	Requires significant materials, labor-intensive installation
Braced Cofferdams	Effective for deep excavations, adaptable to varying soil conditions	Complex installation, higher costs due to extensive bracing
Double-Walled Cofferdams	Superior stability and strength, ideal for high-pressure environments	Most expensive option, time-consuming to install
Earth-Filled Cofferdams	Low material costs, simple construction process	Limited waterproofing, unsuitable for deep water projects

For the Bay Bridge project, sheet-pile cofferdams stood out as the most effective choice. Their ability to form tight seals and resist lateral soil pressures made them well-suited for the soft Bay Mud conditions encountered during construction. This method successfully managed excavations up to 50 feet below the mud line and has since been validated for similar deep-water applications [10].

In contrast, cellular cofferdams are better suited for projects requiring maximum stability. For example, the Panama Canal expansion used cellular cofferdams to create dry work environments, incorporating grout injections and synthetic liners to prevent seepage [18]. However, the Bay Bridge's timeline and budget constraints made sheet-pile cofferdams a more practical solution.

Ultimately, the choice of shoring method depends on several factors, including water depth, soil composition, environmental regulations, and budget. The Bay Bridge project underscored the importance of thorough site assessments - evaluating soil type, water flow, depth, and nearby structures - to determine the best approach [8].

The complexity of installation also varies between methods. The Bay Bridge team's success with sheet-pile cofferdams was due in part to their systematic approach to pile driving and lateral bracing. Their experience highlighted that selecting the right equipment and employing skilled operators are just as critical as choosing the appropriate shoring technique for achieving project success.

Conclusion: Golden State Shoring's Shoring Solutions

The Bay Bridge Skyway Eastern Span project is a prime example of how modern shoring techniques can address the tough challenges of marine construction. Completed between 2002 and 2013, this massive undertaking required cutting-edge engineering to build seismically resilient foundations on unstable bay mud [1][2].

Golden State Shoring has proven its ability to tackle similar challenges, with a strong track record of reinforcing hundreds of properties across the Bay Area. Their expertise in seismic retrofitting and deep foundation engineering ensures their designs not only meet but often exceed earthquake safety standards [19]. By leveraging advanced technology and sophisticated modeling software, the company creates shoring systems that comply with strict building codes while simplifying the permitting process [20].

The Bay Bridge project also highlighted the value of using innovative methods like sheet-pile cofferdams. These custom solutions played a key role in enhancing seismic resilience, helping the bridge achieve its designation as a Lifeline Structure capable of withstanding a massive earthquake expected once every 1,500 years [3]. Golden State Shoring applies a similar safety-first approach, offering services such as soil-structure interaction analysis, temporary support systems, and phased construction strategies to handle the complexities of marine and seismic construction [19].

Their advanced shotcrete techniques stand out as well, cutting project timelines and costs significantly. For instance, these methods saved over $100,000 in demolition expenses and shaved more than two months off project schedules [20][21].

The lessons from the Bay Bridge Skyway project - like the importance of thorough site evaluations, smart material choices, and strict environmental compliance - align closely with Golden State Shoring's systematic methods. Their expertise in excavation support, lateral bracing, and ground improvement ensures success in even the toughest environments [19]. These insights continue to shape their approach to future projects.

Golden State Shoring combines rigorous engineering with practical solutions to address the most demanding construction challenges. For contractors and engineers tackling large-scale infrastructure projects, their proven expertise offers reliable, efficient answers to both marine and seismic construction needs.

FAQs

What are the key benefits of using sheet-pile cofferdams in marine construction projects like the Bay Bridge Skyway Eastern Span?

Sheet-pile cofferdams bring several important benefits to marine construction projects:

They provide a dependable seal to keep water out, ensuring a dry and secure work area.
Built to withstand tough conditions, their strength and durability make them a solid choice for demanding environments.
These structures can speed up construction timelines, which helps lower overall project expenses.
Their adaptability and affordability make them a great option for large-scale projects like bridges and piers.

With their balance of efficiency and strength, sheet-pile cofferdams play a crucial role in marine engineering work.

What seismic design features help the Bay Bridge Skyway remain functional after a major earthquake?

The Bay Bridge Skyway is built to remain functional even after major earthquakes, thanks to cutting-edge seismic engineering. Its standout features include seismic-resistant foundations that keep the structure stable during ground shifts, energy-dissipating decoupling techniques that lessen the force of seismic activity, and specialized pier designs that allow controlled movement in key areas. These measures help the bridge endure powerful earthquakes while reducing potential damage and keeping disruptions to a minimum.

What steps were taken to protect aquatic habitats during the construction of the Bay Bridge Skyway’s Eastern Span?

To protect aquatic habitats during construction, several protective measures were put into place. These included using wave attenuators to reduce erosion and promote seagrass growth, along with advanced noise reduction methods during pile driving to shield marine life from harmful sound levels.

These actions helped keep the impact on the surrounding ecosystem to a minimum, meeting preservation standards while allowing the project to move forward effectively.