Geotechnical Challenges of the Panama Canal
by Andrew Lees, on september 22, 2022
Background - The Panama Canal
In this Ground Coffee blog we highlight some of the geotechnical challenges that had to be overcome for construction of one of the world’s most important infrastructure projects – the Panama Canal.
The canal cuts through the narrow land bridge between North and South America, to allow ships to pass between the Atlantic and Pacific Oceans without having to take the long and hazardous passage around Cape Horn. Construction began in 1881 and the initial plan had no locks, meaning that ships were to pass through at sea level. It soon became clear that the challenge of crossing the continental divide, which rose to 110m above seal level, would not be practicable without locks. The design was therefore revised in 1887 to include two sets of locks. The canal opened to shipping in 1914. With demand for increased capacity over the next 100 years, a scheme for widening and construction of new, larger locks was undertaken and completed in 2016.
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Geotechnical Challenges
The geology of the area is complex, as would be expected at the interface of major tectonic plates. This has created a highly heterogeneous mix of igneous flows and intrusions and softer sedimentary deposits, which in turn has created a number of geotechnical challenges.
In this episode of Ask Andrew, we learn about the geotechnical challenges of the Panama Canal.
The original canal had two lanes, each with a set of locks. Expansion has added a third lane requiring new lock complexes at each end of the canal. There are three lock chambers to raise the ships 27m and each chamber has three lateral water-saving basins. The new locks are massive structures with each lock chamber reaching 427m long, 55m wide and 18.3m deep. At the Pacific end, the upper two chambers are founded on hard basalt rock, while the lower chamber sits on softer clay. The designers have had to contend with significant differences in potential settlement.
Perhaps the most famous engineering challenge overcome by the canal builders is the Culebra Cut: a 13km cutting though the highest ground along the route. Over six thousand men worked in the cut and removed 76 million cubic metres of rock. Almost 23 million cubic metres of this total was additional to the original design, due to the need to remove material from landslides into the cut. A further 1.5 million cubic metres resulting from slides just prior to opening were later removed by dredging. These massive slides resulted from the sloping interfaces between the hard igneous rocks and the softer clay deposits that created a lot of instability. Further multiple landslides continued to occur after the opening in 1915. By 1930, a further 14 million cubic metres of material had been removed.
When the original canal was designed in the late 19th century, little was understood about the factors contributing to slope instability. In 1968, US engineer Arthur Casagrande instigated an observational geotechnical approach, monitoring slope stability along the canal. Information from previous slides was back analysed to better understand the geology and strength envelope of the slope materials. Today there are over 300 monitoring stations along the canal route, recording small movements and rainfall. Data from these monitoring stations is used to predict the onset of landslides so that a pro-active approach can be adopted, and preventative measures put in place where and when needed. Because of these advances in geotechnical engineering, slides today are a very rare occurrence.
Tensar's support of the canal
A further geotechnical problem is erosion of the canal banks. The passage of large ships and tugs create wash that can erode the cohesive soils along the banks. Susceptible sections of the canal are protected by erosion protection mattresses. Tensar Triton mattresses have been used for over 25 years along several major stretches. Further sections have recently been installed on the coastal side of the Atlantic locks. Tensar Triton mattresses are fabricated from durable HDPE Tensar mesh. These are pre-filled with rock before lifting into place from shore or barge.
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Further product details and case studies of similar projects can be obtained from Tensar representatives.
Email us at: info@tensar.co.uk or visit www.tensar.co.uk.