Locks

As before stated there are to be 6 locks on the Panama Canal, 3 at Gatun, 1 at Pedro Miguel and 2 at Miraflores. All of these locks are arranged in duplicate, i.e., at any group of locks a vessel may ascend at one side of the middle wall, while another is descending at the other side. It is the intention that Pacific bound vessels use one side and Atlantic bound the other.

The middle wall is to extend 1,600 feet above the upper gates and below the lower gates as an approach wall against which vessels to be locked may lie while waiting for the gates to open. The side walls will not be as long, and will flare out at their ends. The lock chambers are to be 110 feet wide and 1,000 feet long and will pass vessels of 40 feet maximum draught in sea water. The upper lock in each flight is to be subdivided by additional gates into a 600 foot and a 400 foot lock so that water may not be needlessly wasted in passing small boats. These smaller subdivisions may be used until vessels of over 550 feet length require passage.

The lifts will average 28 feet, but will vary with changes in tide, lake level, and conditions of lockage. The diagram below shows the entire lock system at Gatun.

Near the bottom of each wall will be a large culvert for passing water from the lakes into the upper chamber, and from chamber to chamber, and then out to the canal below the locks. The intakes (See Fig.2) will be located at “I” and outlets at “O”. The water enters and leaves the culverts through several small openings, the intakes being screened. The flow of water in the culverts is to be controlled by what is called the Stoney type of valves. These valves occur in pairs which are duplicated at each of the lifts so that if one pair is disabled the other set may be used while repairs are being made. On each side wall, at the middle gates in the upper lock there will be only one set of valves, but none in the middle wall. The flow between the culvert in the middle wall and the lock chamber is to be controlled by cylindrical valves capable of withstanding pressure on both sides. By using these valves water may be saved under certain conditions of lockage by cross-connecting the twin chambers through the middle wall.

In each chamber 11 laterals of 41 square feet cross-section will be led from the side wall culverts while at the middle culvert there will be 10 laterals having a minimum cross-section of 33 square feet. Each lateral will have five holes, each of 12 square feet area, opening up through the lock floor. The laterals leading from the middle wall culvert are to be controlled individually to provide for independent operation of the twin chambers.

The lake levels and the desired lock levels are to be maintained by large steel miter gates. At the upper and lower end of the upper chambers of all locks there will be two sets of these gates operated simultaneously so that a vessel entering the upper chamber will always have two pairs of gates between it and the lake. At the lower end of each flight, besides the regular gates there will be guard gates mitering in the opposite direction. They are intended primarily for holding back the water in the canal below, when the lock above is unwatered for repairs but may be operated during lockages purely as a safeguard.

As a protection to the gates heavy fender chains are to be stretched across the locks at critical places. They are designed by suitable retarding devices to bring a slowly moving vessel to rest before it can strike the gate. While the gates below are being opened the chains drop into recesses in the walls and across the floor. Near the upper end of the locks and 200 feet above the uppermost gate, an emergency dam of the swing bridge type will be provided to be used in case of accident to the upper gates.

The following precautions against accident are to be observed:

First. All vessels must stop some distance from the gates.

Second. The lock operators here take the vessel in charge and control its passage through the locks.

Third. If a vessel breaks away from the operators or fails to stop at the proper place, it comes against the heavy chains stretched across the locks and is either brought to a full stop or is greatly retarded.

Fourth. In case a chain breaks, the vessel has two sets of gates to break, if at the upper level, where an accident would be most serious. Should all these barriers fail the emergency dam can be swung into place in a very short time.

The floors of the Miraflores and Pedro Miguel locks will have 1 foot thickness of concrete on top of the rock as a wearing surface. At Gatun, however the rock is of a character susceptible to the weather. It has therefore been considered necessary, in constructing the floor here, to leave the rock above grade until just before the concrete is to be placed and then to scrape and wash the surface to be covered. The floor in the lower portion of the upper chamber is to be of concrete 3 feet thick. The rock here is considered thick enough to withstand the pressure from the water-bearing stratum below. Above the middle gate, however, this stratum is too thin, and a floor 13 feet thick of concrete is provided and anchored by rails set in holes and surrounded by concrete.

The main floor level will be about 2 feet below the sills, in order that small objects dropped from vessels may be passed without being struck.

The sills for the gates are designed as concrete arches in a horizontal plane, 31 feet thick throughout and of 100 feet radius at the extrados.

The filling system is designed so that, with all valves opened the chamber can be filled in 8 minutes, but to prevent possible damage to vessels in the lock the maximum rate will probably not be allowed to exceed 3 feet a minute which would correspond to less than 15 minutes for filling.

Most of the foregoing discussion is taken from the Engineering Record of February 26, 1910.

There has been much criticism of the lock sites, but the engineers now in charge seem to have perfect confidence in their work.

During the fiscal year 1908–’09 the work of excavating for the Gatun locks was continued by steam shovels and one 20-inch suction dredge. Material excavated in the dry amounted to 933,546 cubic yards, and that in the wet to 479,950 cubic yards. It was decided to construct curtain walls to stop any underflow; these will extend across the lock under the sill of the emergency dam and downstream outside the walls to the intermediate gates. As an additional precaution to making the concrete floor 13 feet thick as before mentioned a system of sumps under the floor with telltales in the walls will be built.

The plant for the construction of the locks is practically installed and ready for work, it being operated entirely by electricity.

At the Pedro Miguel locks 715,726 cubic yards were removed in 1908–’09. One lock chamber was completed to grade, but 45,000 cubic yards remain for removal in the other one.

At Miraflores work was done the past year with steam shovels and one suction dredge. The total amount excavated was 1,147,527 cubic yards which is one-half of the total estimated quantity.