science, health & technology

 

On February 13 Panama Canal Authority (ACP) engineer Rodrigo Lam Manfredo, with his grandfather (former canal administrator Fernando Manfredo) and Little League coach (John Carlson) in the audience, spoke to the Panama Historical Society about the canal's history from an engineering point of view.

 

The building of the Panama Canal is a famous feat about which much has been written. A lot of what happened, however, isn't popularly known.

 

Yes, the French failed amidst epidemics and financial scandals, but they also did a lot of the excavation at Culebra Cut. The early American decision to stop canal construction work and concentrate on making the area livable is also famous, but the geology behind the construction era's deadliest accidents is less well known.

 

"The geology of the canal is very erratic," Lam explained. It's a complicated series of soil and rock layers, with geological roots in a volcanic archipelago that arose from the Caribbean sea, was built up by accretions of coral as it slowly moved on tectonic plates, got crunched and shoved and folded and metamorphosed as it jammed itself among several plates and into the gap between the North and South American land masses, then aged and grew for  a few million more years until the present time. It's a great lab for studying soils. "A lot of the theory of soil mechanics," Lam pointed out, "come from the Panama Canal."

 

It wasn't as if that knowledge and theory were known when the canal was being built. The original projections of how much earth needed to be excavated to make Culebra Cut were much lower than turned out to be necessary, as shown by the great landslides that happened soon after the canal opened and closed the waterway for the better part of a year in late 1914 and early 1915. The cut's banks have never reached the angle of repose at which landslides don't happen, despite more than a century of excavation. For decades after the canal opened, the excavation and dredging was to provide a buffer zone against landslides, and only recently has the widening work been for the purposes of widening and straightening the navigation channel.

 

Along the way the canal management tried many things to stabilize the banks, including the use of lime to remove water from the soil and the planting of Vietnamese elephant grass (paja canalera) to hold the soil. The problem is that the critical zones are further underground than these surface measures affect, to the depths where where loose soil layers lie atop smooth rock layers and the addition of water can lubricate the slide of acres at a time into the canal. The ACP has a modern electronic soil monitoring system and tries to direct surface water away from critical spots. It's still not a sure science, so whenever the canal authority's meteorologists indicate that heavy rainstorms are coming those in charge of dealing with landslides go on heightened alert.

 

So are mixtures of soil and water always a canal engineer's worst nightmare?

 

Actually, no. The Gatun Dam --- that 2.6-kilometer berm of which the spillway is just a small part --- is hydraulic fill. That is, it's muck, a mixture of water, dirt and sand that was pumped into place and then compacted during the canal's construction. It has held up well over the years, but won't be able to serve all of functions that it did when the waterway is expanded.

 

It's not that the dam is particularly unstable, but that with Gatun Lake's water level being raised for the expansion the spillway's gates won't work. Thus the plan is to build a new dam with a new spillway to the west, which will empty into the Caribbean Sea near Rio Indio. The old dam, Lam said, will be retrofitted to handle the higher lake level.

 

In the expansion a new type of locks will be built for the larger post-Panamax ships. These will be the largest and steepest locks with water-saving basins yet to be built, and one of the changes from the European-style locks that is planned is for the basins to empty out into the bottom of the lock chamber instead of from the side, to avoid the tricky cross currents that cause so many ships using Europe's locks with basins to smash into the lock walls.

 

Meanwhile the old locks are not going to be abandoned, and their maintenance and improvement are also undergoing constant modernization processes.

 

With the rise of the Panamax freighters, the mules --- locomotives --- that pull the ships through the locks had to pull more weight, and that meant that the tow tracks had to be strengthened and more powerful new mules had to be acquired.

 

(The plan for the new locks is not to use mules, but rather to have tugboats that pass through the locks with the ships.)

 

Maintaining the lock gates has always been a daunting task. The 700-ton steel structures are hollow and airtight, which means that they can be moved with much less force than one might suppose (formerly a gear system with a 40-horsepower motor did the job, but now they are moved by a hydraulic arm system). When maintenance time comes, the gates can be floated away and towed to the Industrial Division drydocks in Mount Hope. The drydocks have over the past few years been undergoing a major expansion and modernization. When they get to Mount Hope, the gates don't get entirely taken apart but rather are closely inspected, with repairs and replacements made on a preventive maintenance model especially at the points where mathematical models tell engineers that the steel is under the highest stress.

 

(The new locks will have gates that slide into the locks wall, making it possible to do maintenance work while they are in place.)

 

These days the critical bottlenecks are not the locks, but Culebra Cut. That channel across the Continental Divide has already been widened from 300 to 500 feet, and though the pilots' union won't accept it as a safe regular practice, it has been shown that two Panamax container ships can pass one another in the cut without incident. The cut is in the process of being further widened and straightened, with a goal of a channel that's 630 to 700 feet wide and useful for everyday two-way traffic by large ships.

 

The really daunting new digging for the canal expansion, however, will be on the Pacific access channel to the new locks. This channel will bypass Miraflores Lake and locks and lead to the new locks on Culebra Cut near Pedro Miguel. But in order to make this work, not only will there have to be excavation, but also at low-lying points along the channel there will have to be some large earth and stone levees to keep the water in.

 

So what does Lam's grandfather, one of the strongest critics of the canal expansion that was approved in October of 2006, think about it now? From an engineering perspective, Fernando Manfredo is confident that there are competent engineers on the job and that when the additions to the canal are done they will work. However, he told this reporter that he is as strongly convinced as he was before that the expansion will probably be a financial disaster for Panama.