Centenario Bridge - Panama

The Panama Canal is famous as a unique shipping link between the Atlantic and Pacific Oceans. The fantastic engineering challenges surmounted during the construction, coupled with the heroic human effort, only adds to the bridges notoriety. Although the 80 km long Canal connects two oceans, shortens shipping routes dramatically, and separates the North and South American continents, the bridges' primary purpose is to provide four-lanes for vehicular traffic across that Canal connecting the Isthmus of Panama. Until 2004, the Bridge of the Americas was the only way to cross the Canal.

In 2002, grading and foundation work began for a new cable-stayed bridge, known simply as Second Bridge over the Panama Canal. Overseeing the US $93 million contract for construction of this world-class 3800 foot span is Bilfinger-Berger AG for the Panamanian Ministry of Public Works.

The new bridge is located a few hundred yards from the infamous Culebra Cut, known to engineers not only as the narrowest point in the canal, but also as the location of a flow slide that actually closed the canal for 24 hours in 1986.

For geotechnical engineers, this area has an intimidating reputation stemming from the uncertain geotechnical properties of the subsurface volcanic deposits, locally referred to as the Cucaracha formation. Samples of the Cucaracha, in addition to exposed sections of the formation, exhibit significant loss of shear strength and ultimate disintegration after being exposed to air. Clearly, designing bridge foundations in an area of such geotechnical uncertainty presented a unique challenge for the project engineers. When engineers face uncertainty of this nature, they turn to Osterberg cell (O-cell®) technology, provided by the professionalism and experience of LOADTEST.

O-cell testing was specified on three 2.0-meter drilled shaft foundations to help define ultimate capacities of the foundation elements and provide settlement information at various multiples of the design working loads. The O-cell tests were carried out to loads exceeding 70 MN (16,000 kips). Test results indicated unit side shear resistances varying between 90 kPa and 450 kPa. Measured end bearing values were on the order of 5 MPa at tip displacements of roughly 5 % of the shaft diameter.

While the unit resistance values were much higher than anticipated and those predicted by empirical methods, high variability in subsurface conditions over short distances limited the engineers’ ability to use the test data to economize on the foundation design. By utilizing O-cell technology and performing the first and only full scale static load tests on drilled shafts in the Canal area, the data provided a level of comfort and confidence that manifests whenever uncertainty is reduced.

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Centenario Bridge - Panama

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