A special equipment was required to haul the sand, gravel, and cement from the storage piles to the concrete mixers. There were two circular railroads of 24-inch gauge, carrying little electric cars that ran without motormen. Each car was stopped, started, or reversed by a switch attached to the car. Their speed never varied more than 10 per cent whether they were going empty or loaded, up hill or down. When a car was going down hill its motor was reversed into a generator so that it helped make electricity to pull some other car up the hill. The cars ran into a little tunnel, where each was given its proper load of one part cement, three parts sand, and six parts gravel—2 cubic yards, in all—and was then hurried on to the big concrete mixers. These were so arranged in a series that it was not necessary to stop them to receive the sand, gravel, and cement, or to dump out the concrete.
On the emptying sides of the concrete mixers there were other little electric railway tracks. Here there were little trains of a motor and two cars each, with a motorman. The train, with two big 2-cubic-yard buckets, drew up alongside two concrete mixers. Without stopping their endless revolutions the mixers tilted and poured out their contents into the two buckets, 2 yards in each. Then the little train hurried away, stopping under a great cable. Across from above the lock walls came two empty buckets, carried on pulleys on the cableway. When they reached a point over the train they descended and were set on the cars, behind the full buckets. The full buckets were then attached to the lifting hooks, and were carried up to the cable and then across to the lock walls, where they were dumped and the concrete spread out by a force of men. Meanwhile the train hustled off with its two empty buckets, ready to be loaded again.
On the Pacific side the concrete handling plant was somewhat different. Instead of cableways there were great cantilever cranes built of structural steel. Some of these were in the shape of a giant T, while others looked like two T's fastened together. Here the clamshell dippers were run out on the arms of the cranes to the storage piles, where they picked up their loads of material. This was put in hoppers large enough to store material for 10 cubic yards. The sand and stone then passed through measuring hoppers and to the mixers with cement and water added. After it was mixed it was dumped into big buckets on little cars drawn by baby steam locomotives, which looked like overgrown toy engines. These little fellows reminded one of a lot of busy bees as they dashed about here and there with their loads of concrete, choo-chooing as majestically as the great dirt train engines which passed back and forth hard by. The cranes would take their filled buckets and leave empty ones in exchange, and this was kept up day in and day out until the locks were completed. When the plant was removed from Pedro Miguel to Miraflores, a large part of the concrete was handled directly from the mixers to the walls by the cranes without the intermediary locomotive service.
The cost of the construction of the locks was estimated in 1908 at upward of $57,000,000. But economy in the handling of the material and efficiency on the part of the lock builders cut the actual cost far below that figure. On the Atlantic side about a dollar was saved on every yard of concrete laid—about $2,000,000. On the Pacific side more than twice as much was saved.
Before the locks could be built it became necessary to excavate down to bed rock. This required the removal of nearly 5,000,000 cubic yards of material at Gatun. Then extensive tests were made to make certain that the floor of the locks could be anchored safely to the rock. These tests demonstrated that by using the old steel rails that were left on the Isthmus by the French, the concrete and rock could be tied together so firmly as to defy the ravages of water and time. A huge apron of concrete was built out into Gatun Lake from the upper locks at that place, effectively preventing any water from getting between the rocks and the concrete lying upon them.
CHAPTER V
THE LOCK MACHINERY
One of the problems that had to be solved before the Panama Canal could be presented to the American people as a finished waterway, was that of equipping it with adequate and dependable machinery for its operation. Panama canals are not built every year, so it was not a matter of ordering equipment from stock; everything had to be invented and designed for the particular requirement it was necessary to meet. And the first and foremost requirement was safety. When we look over the canal machinery we see that word "safety" written in every bolt, in every wheel, in every casting, in every machine. We see it in the devices designed for protection and in those designed for operation as well. We see it in the giant chain that will stop a vessel before it can ram a gate; we see it in the great cantilever pivot bridges that support the emergency dams; we see it in the double lock gates at all exposed points; we see it in the electric towing apparatus, in the limit switches that will automatically stop a machine when the operator is not attending to his business, in the friction clutches that will slip before the breaking point is reached. Safety, safety, safety, the word is written everywhere.