How do multi-disciplinary firms help solve the challenges of complex PPP (concession) projects overseas?

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Langan serves as technical advisor to the lenders (LTA) for EKPPT Motorway in Peloponnese, Greece.

By nature, public–private partnership (PPP or 3P or P3) projects are collaborative and multi-disciplinary. PPP projects have numerous stakeholders, multiple success criteria, longer time horizons, and greater risks in procurement and delivery. The ultimate goal is achieving a balance between risk and return. Therefore, the PPP project model requires numerous specialists to access and address a variety of technical, environmental, contractual, and financial aspects.

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EKPPT Motorway will link Athens and Korinthos to the western end of the Peloponnese.

The role of the Lender’s Technical Adviser in a PPP not only requires excellent technical background, but also an understanding of the bigger picture.  During the tender and construction phases, Langan liaises with the involved parties and provides lenders with risk assessments for environmental permitting, designs and construction methods, project schedule, and robustness of CAPEX and OPEX. As a multidisciplinary firm with extensive experience in complex construction projects, Langan has been able to provide high quality Lender’s Technical Adviser services, help cross-disciplinary and cross-functional conflicts, and move the project forward.

About Tasos Papathanasiou, PE
Tasos has over 18 years of diversified experience managing large scale multi-disciplinary projects, including geotechnical and environmental investigations, site evaluations, foundation design, bulkhead design, construction oversight, and stormwater management. He has provided technical advisory services for motorway and airport concession projects in Greece, Cyprus, and Eastern Europe.

What challenges did you encounter while working on the SFMOMA project?

Project Background and Challenges
The expanded San Francisco Museum of Modern Art (SFMOMA), designed by lead architect Snøhetta, opened last month. The 10-story steel-framed structure stands 210 feet above the adjacent streets.

Originally designed in 1991, the museum’s foundation system consisted of a relatively thin mat that extended beyond the structure’s limits to support a future seven-story expansion. Two decades later, expansion plans revealed that the museum needed more space than originally planned.

The expansion combines the existing mat foundation with the new foundation. The project also added a basement, which required a 30-foot-deep excavation in a heavily dense urban area.

Langan faced the following geotechnical challenges:

  • Differential settlement between the existing and new foundations
  • Temporary support of the adjacent 32-story W Hotel during the planned excavation for the new basement
  • Weak and potentially liquefiable soil underlying the new mat foundation
  • Presence of relatively thick deposit of moderately compressible soil
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Construction at the SFMOMA site.

Our Solutions
Langan was a key member of the project team, working closely with Magnusson Klemencic Associates (project structural engineer) and Webcor Builders (project general contractor). As the geotechnical, earthquake, and environmental engineers, we developed performance-based seismic design criteria and foundation solutions so the project could move forward.

To address the geotechnical challenges, we recommended deep soil-cement mixing (DSM) to improve the ground beneath the new basement and provide temporary shoring. The objective of the ground improvement was to: (1) reduce the potential for liquefaction, (2) reduce the potential for disturbing the weak underlying soils during construction, and (3) transfer building loads to deeper competent layers.

The DSM panels provided appropriate subgrade bearing for the mat and brought the anticipated differential settlement to acceptable levels. For the original mat foundation, MKA developed a system of stiff shear walls through the basement to spread heavy column loads to meet Langan’s geotechnical and foundation design criteria. This structural system not only supported the original mat without overstressing it, but it also allowed the structural connection to the new mat foundation.

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SFMOMA reopened in May 2016. The transformed museum, with its new (white) addition visible behind the distinctive original building, has twice the amount of exhibition space as before. (Credit: Michael Layefsky)

For the required 30-foot-deep excavation, we developed geotechnical design criteria for a stiff soldier beam and raker system to support the neighboring 32-story W Hotel. Ground improvement was also used to strengthen and stiffen the subgrade soil supporting the shoring. Small measured excavation-induced displacements confirmed the success of this approach.

With our interactive solution-oriented approach with the design and construction teams, we overcame project challenges. The majestic SFMOMA is a testament to our innovative and adaptable foundations systems.

Answer provided by Scott Walker, PE, GE, Associate
Scott has over 17 years of experience in providing geotechnical investigation, design, consultation, earthquake engineering, and construction observation services for projects throughout California and southwestern Montana. He specializes in providing innovative geotechnical solutions to challenging sites. His experience includes: commercial and residential buildings, high-rises, sports facilities, museums, schools, and resort development.