Guiness Book of World Record holder and recognized in ASCE’s Historic Civil Engineering Landmark Program in 2013, Louisiana’s Lake Pontchartrain Causeway, a toll bridge which spans over Lake Pontchartrain from Causeway Boulevard in Metairie, Louisiana to Highway 190 at Mandeville, Louisiana; opened in 1956 with an the original span of 23.86 miles, glissading in most places just 16ft above the water’s surface. Back in the day it was the longest bridge over water in the world, but in 1969 its sister, at 23.87 mile, took the title. The Causeway Bridge consists of two parallel bridges designed and constructed in different periods of time. The original bridge is on the West, it opened in 1956 and carries traffic from North to South and costed $46 million. The second bridge on the East was completed 13 years later for an additional $30 million and opened in 1969; carries traffic in the opposite direction. The causeway was the first to utilize pre-stressed concrete and prefabricated modular components on a large scale.

The Causeway Bridge was constructed to connect New Orleans and Mandeville, allowing for decreased travel time throughout that part of the state. The bridge took just fourteen months and it is still the longest continuous stretch of bridge over water in the world decades after it was first commissioned. The causeway is supported by 9,500 pilings and is so stable that it has suffered a minute amount of damage from major hurricanes and storms in comparison to any other causeway worldwide. The causeway’s opening reduced the drive time to New Orleans by upto 50 minutes thus, helping the small North Shore communities substantially. It has reasonably sound structural condition, nearly 60 years of age and has endured harsh site conditions such as brackish water and high humidity.

Design, Construction And Engineers
Palmer and Baker, Inc. designed the first bridge to exclusively consist of identical panels, caps and pilings. The 56’ long and 33’ wide spans were rigidly cast to allow for all pieces of the bridge to be fabricated ex-situ, minimizing cost and time required to construct such a large structure. Many engineers consider ‘Accelerated Bridge Construction’ (ABC) as a new and innovative bridge engineering and was carried out in this project. The second bridge was designed by David Volkert & Associates in the mid 1960’s and it’s construction began in 1967. This structure’s typical span is made of 84’ long and 33’ wide with Precast Prestressed members.

Two factors contributed to why the bridge received a distinction:

» The civil engineers who worked on the project

» The innovative techniques used during construction

Dr. Maxwell Upson, Chairman of the Board of Raymond Concrete Pile Company, one of the largest contracting companies for foundations in the United States, was an innovator in the field of prestressed concrete, particularly in pile fabrication and installation. He saw prestressed concrete as a way to break down the barriers that once limited how piles could be installed. Before Dr. Upson’s research, most concrete piles were square with dimensions of 24 inches or less. He saw potential for using piles with dimensions of 36 to 54 inches. Some of the other engineers working with Dr. Upson were Henry LeMieux, District Manager for the Raymond Concrete Pile company, who was instrumental in promoting the use of the 54 inch prestressed concrete piles; Walter Blessey of Tulane University who was responsible for research and testing of the prestressed concrete elements and who help advance the technology were all contributors to the causeway 60 years ago.

Louisiana soil, which is made up of soft clays and silts, does not develop large tip bearing capacities and require that piles be driven deep until sufficient resistance is developed to support the load. Therefore, these large, prestressed hollow piles were ideal for developing the foundation for a bridge since they could withstand the hammer blows needed to drive the piles deeper into this type of soil.

Once they decided that these larger hollow cylindrical prestressed concrete piles could be used for their bridge foundation, the civil engineers needed to develop a design and method of construction. Given that the contract required construction of the 24-mile span in only 23 months, the engineers devised a rather simple structure - two piles straddled by a bent cap supporting the ends of two 56 foot decks. This simple layout is repeated over and over. By making the components (piles, bent caps and decks) identical, Upson, Blessey and the engineers at Palmer and Baker could employ the theories of mass production to build this bridge. A concrete casting plant was built at the northern end of the bridge; the components were prefabricated and then barged out via the Lake to the construction site. This assembly line process significantly reduced both the construction cost and the installation time.

*Satellite Image of the Causeway Visible Crossing Lake Pontchartrain*

Hurricane Katrina
The hurricane hit New Orleans in August of 2005 and very little damage was sustained to the causeway, as only 17 spans were lost, but the bridge’s integrity remained. The nearby I-10 twin span bridge did sustain a large amount of damage and was not usable for a considerable time. As a result, the Lake Pontchartrain Causeway became a vital transport line for the region. It was opened first for emergency services only and allowed recovery and rescue teams to travel back and forth from the north and south shores with relative ease.

This open pathway was significant in enabling aid to reach those in teams more quickly than it would have if the bridge had been damaged.

The cause reopened to the general public roughly two and a half weeks after the storm hit. Due to the storm’s severe trauma and financial toll, the bridge did not charge tolls for roughly the first month of its reopening. The storm and the resulting use during the emergency reinforced the importance of the causeway, and its benefits to the communities on either side of it.

It is a marker of the infrastructure advancements to note that this particular bridge, even as the longest, has shown no significant natural damage to date. However, repairs and continued improvements are inevitable over time. Modern Marvels spotlights the Lake Pontchartrain Causeway: ‘The Causeway actually traverses roughly 1/1000th of the earth’s circumference. Whatever the Causeway may lack in visual flamboyance, it makes up for in engineering and endurance.,’ Modern Marvels reports.

Reference
1. https://abc-utc.fiu.edu/wp-content/uploads/ sites/52/2020/01/paper-58-THE-CAUSEWAYBRIDGE-CONSTRUCTION-PAST-PRESENT.pdf
2. https://www.asce.org/about-civil-engineering/ history-and-heritage/historic-landmarks/lakepontchartrain-causeway-bridge/
3. https://v olkert.com/projects/lake-pontchartrain-causeway/

By -
Tuhina Chatterjee, Associate Editor Civil Engineering and Construction Review

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