Modern vessels and normal deterioration have conspired to force redesign of the Panama Canal locks’ hydraulic systems. Completed last week, the latest retrofit differs from earlier ones in that an outside contractor was called in to use new drilling techniques.

When completed 72 year ago, the locks were engineering marvels. The 1,000 foot long x 110 foot wide lock chambers could contain the largest ships of the day. But marine architects have since designed ships with vertical sides that fit so snugly into the lock chambers as to restrict maintenance work.

Major 18 foot diameter culverts run along both sides and under the center wall of the two sets of locks. Lateral culverts carry the water to or from these main culverts, distributing or draining the water from all regions of the chamber at once. The lateral culverts run to either the fill or drain culverts. Since any single main culvert can fill or drain in the chamber, one set of lateral culverts can be plugged to allow maintenance to proceed in its main culvert.

But the technique to block a main culvert inserting mushroom shaped steel caps into the lateral culverts’ week holes, was made obsolete. As the tight fitting canal ships passed through the chambers, they tended to suck the caps out – making maintenance work in a main culvert adjacent to an active lock chamber somewhat nerve-racking with the prospect of a sudden flood imminent.

In 1969, at the Pedro Miguel Lock, the Panama Canal Commission’s (PCC) maintenance division cut slots into the lock floor at the junctions of the lateral and main culverts. Steel frames cemented into the slots allowed canal maintenance crews to easily insert bulkheads that effectively isolated the main culverts from the lock chamber. But drilling out the bulkhead slots was done with rotary percussion track mounted air drills. “It was very noisy, dirty and dusty,” says Herman A. Erhart, Jr., project manager for PCC.

Searching for a new technique to cut the slots, the maintenance division brought in Concrete Coring Company to drill the holes for a cathodic protection system from the top of the walls of the Gatun Locks to valves in the main culverts. Using diamond core drills, the 3 inch x 56 foot holes were drilled so accurately, quickly, cleanly and quietly that the commission agreed to try the technique on the major retrofit of the Gatun Locks’ hydraulic system. PCC normally does its own maintenance work.

The contract was awarded to Concrete Coring Company. Phase one – stitch-drilling to create the slots in the three east chambers – started on January 18 under a tight 14 day schedule. Work was slowed by heavy rains and by shifts in the work schedule. About 1,000 men were working on the lock rehabilitation. Concrete Coring Company crews had to leapfrog around the lock floor to give PCC maintenance crews space to install the bulkhead forms.

But while slickers can protect against rain and fast footwork can ameliorate crowding, only brute force could get the drillers around the time-capsule surprises they found in the lock floor. While stitch-drilling, Concrete Coring Company crews started to hit steel rails in the lock floor’s concrete, which was supposedly not reinforced. The crews double-drilled around, and then burned out the rails.

Once drilling was completed, workers went into the culverts and broke off the base section, slung cables around the plugs and hoisted them out.

After phase one was finished, work stopped for two weeks to allow full ship traffic to resume. On phase two, on the west locks, work went much more smoothly. Concrete Coring Company used larger bits and brought in a few more laborers. They took only eight days to finish the 14 day job.

Concrete Coring Company drilled out 107 slots in the six lock chambers. Besides the bulkhead work, the PCC maintenance crew spruced up the lock’s massive miter gates and refurbished their sills. Cathodic protection systems installed on the new steel bullhead frames, and these systems – along with the bulkheads’ promise of easier maintenance – should keep traffic flowing smoothly through the canal for another 72 years.

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