Temporary Structural Shoring for Golden Gate Bridge Retrofit

Joe Lazzaretti
Sep 16
6 min read

Keeping the Golden Gate Bridge Safe During Retrofit Work

The Golden Gate Bridge retrofit focused on improving earthquake resistance without disrupting traffic or altering the bridge’s historic design. Temporary structural shoring was key to maintaining safety and stability during construction. This process used steel frameworks, hydraulic jacks, and concrete supports to manage heavy loads while crews worked on upgrades.

Here’s what made the project stand out:

Seismic Upgrades: Strengthened foundations and replaced isolation bearings to handle earthquakes.
Traffic Continuity: Kept the bridge open during construction to avoid economic and safety issues.
Advanced Monitoring: Sensors tracked load shifts and environmental conditions in real time.
Custom Equipment: Cast-In-Drilled-Hole (CIDH) piles provided reliable support during foundation work.

The retrofit team also used a collaborative planning method, engaging contractors early to address challenges like load redistribution and site access. These lessons can guide future infrastructure projects, especially in earthquake-prone regions.

TYPICAL ADVANCE SHORING BRIDGE CONSTRUCTION, (MSS)

Engineering Problems in the Golden Gate Bridge Retrofit

Retrofitting the Golden Gate Bridge required balancing complex load management with preserving its historic character - all while ensuring traffic could continue to flow. This effort demanded innovative solutions, particularly in the realm of shoring and load redistribution.

Load Transfer Challenges

The seismic retrofit of the North Approach Viaduct, completed between 1996 and 1999 [1], is a prime example of the intricate engineering required to address load transfer issues.

To strengthen the structure, engineers transformed the original five-span simply supported truss into a partially continuous system. This involved replacing towers and foundations while incorporating temporary supports to carefully manage load redistribution throughout the process [1]. By modifying the bottom chord, they enabled seismic forces to be distributed laterally across all towers, enhancing the bridge's structural resilience [1]. Additionally, the installation of new isolation bearings replaced the older ones, further improving the management of loads under seismic activity [1].

Shoring Solutions and Equipment Used

Cast-In-Drilled-Hole (CIDH) Piles

When it came to ensuring foundation stability during the retrofit, Cast-In-Drilled-Hole (CIDH) piles proved to be an essential solution. These reinforced concrete piles were a key element of the temporary foundation support system. They are created by casting concrete into predrilled holes, offering reliable support throughout the construction process [2].

The effectiveness of CIDH piles depends heavily on the soil's ability to maintain the hole's shape during concrete placement [2]. In cases where groundwater or loose soil threatened the hole's integrity, temporary steel casings were used to stabilize the structure until the concrete was poured [2]. To prepare the hole properly, specialized cleanout buckets were employed to clear out loose debris, ensuring a firm and level bottom for the pile [2].

While CIDH piles are considered one of the more cost-effective piling options, installations with diameters exceeding 24 inches often require additional measures. For instance, even in "dry" conditions, inspection pipes are necessary when dewatering is involved to ensure the quality and safety of the installation [2].

Project Examples and Lessons Learned

Project Coordination Methods

Once the engineering challenges were identified, ensuring smooth project coordination became a top priority. To tackle these complexities, the Golden Gate Bridge retrofit adopted the Construction Manager/General Contractor (CMGC) delivery method specifically for temporary shoring. This approach was designed to address earlier issues with load transfer and site access. The Golden Gate Bridge, Highway and Transportation District approved this method in July 2018, and Project #1923 officially began in April 2019 [3].

During the preconstruction phase (May 2024–September 2025), the prime contractor played a consulting role. Their expertise in constructability allowed the project team - which included the engineer/designer, CMGC contractor, and an independent cost estimator - to create accurate cost models, perform detailed risk assessments, and develop mitigation strategies [3].

In March 2025, the Federal Highway Administration (FHWA) conducted a Cost Schedule Risk Assessment (CSRA) workshop. This workshop used probabilistic methods to estimate costs, a required step for projects exceeding $500 million in scope [3].

The collaborative work established during preconstruction proved invaluable. By identifying and addressing potential challenges early, the team set the stage for a smoother execution of the retrofit in later phases. This proactive and well-coordinated approach became a cornerstone of the project's overall success.

Key Takeaways for Future Infrastructure Retrofits

Critical Success Factors

The success of the project hinged on early planning, thorough risk assessments, and a collaborative approach. By combining the expertise of engineers, designers, and contractors, the team developed accurate cost models and identified potential constructability challenges early in the process. This proactive strategy was essential in managing both costs and risks effectively.

One standout aspect was the use of flexible shoring solutions tailored to the site’s complex conditions. For instance, custom-built drilling equipment, paired with modified Cast-In-Drilled-Hole (CIDH) piles, highlighted the importance of adapting standard solutions to meet unique project demands. Engineers should anticipate the need for equipment customization to address specific site challenges.

Another critical element was the integration of continuous load monitoring systems. These systems not only ensured the structural integrity of the project but also safeguarded public safety - emphasizing the importance of incorporating such measures from the very beginning.

These factors collectively provide a strong foundation for applying shoring innovations to future infrastructure projects beyond the Golden Gate Bridge retrofit.

Future Applications of Shoring Methods

The lessons learned from this project open the door to broader applications of these shoring methods in various retrofit scenarios. Here’s how these approaches can be applied in the future:

CIDH Piles with Tiedown Anchors: This method, which addresses both vertical load transfer and lateral stability, is ideal for seismic retrofits in earthquake-prone areas. It offers a practical template for enhancing the resilience of critical infrastructure.
Temporary Tower Systems with Seismic Isolation: These systems provide a versatile solution that extends beyond bridge retrofits. They can support highway overpasses, elevated transit structures, and other key infrastructure during modernization projects, ensuring service continuity throughout upgrades.
Preconstruction Consulting Model: Engaging contractors as consultants during the design phase proved invaluable. This approach not only helped identify constructability issues early but also led to more accurate cost estimates, reducing delays and minimizing change orders.
Innovative Site Access Solutions: Techniques such as specialized equipment positioning and strategic material delivery offer practical benefits for urban bridge retrofits, waterfront structures, and projects in environmentally sensitive areas.

FAQs

How is safety and stability maintained during the Golden Gate Bridge retrofit using temporary structural shoring?

Temporary structural shoring plays a crucial role in maintaining the safety and stability of the Golden Gate Bridge during its retrofit. This is achieved through the use of engineered support systems such as modular beams, braces, and sheet piling. These components are carefully designed and continuously monitored by expert engineers to strengthen the structure and eliminate the risk of collapse during the construction process.

This method not only safeguards the bridge’s core structure but also prioritizes the safety of workers and the surrounding area throughout the retrofit. By addressing the complexities of large-scale projects, temporary shoring ensures the bridge remains stable, even under challenging conditions.

What challenges arise when transferring loads during the seismic retrofit of the Golden Gate Bridge?

Managing the load transfer during the seismic retrofit of the Golden Gate Bridge comes with its own set of challenges. One of the main concerns is making sure seismic forces are safely redistributed across the bridge’s older structural elements, like concrete and steel, without putting its stability at risk. The aging materials and the uneven distribution of forces make this process even more complicated.

To tackle these issues, engineers rely on advanced methods such as jacketing, which reinforces structural components, and energy dissipation devices, which help absorb seismic energy. These carefully planned solutions are designed to preserve the bridge’s integrity, keeping it functional and safe both during and after seismic events.

What key lessons from the Golden Gate Bridge retrofit can be applied to improving infrastructure in earthquake-prone areas?

The Golden Gate Bridge retrofit highlights the importance of modern materials and methods, like post-tensioning and geotechnical solutions, in reinforcing structures to withstand earthquakes. These techniques help enhance a structure's ability to endure seismic forces, ensuring greater stability during such events.

Some key points to consider include tackling soil instability, following seismic safety regulations, and integrating real-time monitoring systems to observe how structures perform over time. By leveraging these methods, engineers and builders can create infrastructure that is both safer and more durable in earthquake-prone areas.