THE LOCKS.
The Panama Canal belongs to the "age of concrete." All other vast works
of construction, such as the Pyramids of antiquity and the Assouan Dam
of to-day, have been built of live natural rock. At Panama
everything--locks, wharves, piers, breakwaters--has been constructed of
concrete. The Americans have not only built these incomparable piles of
masonry; they have manufactured the material out of which they are
built. This circumstance makes the rapid completion of the canal all the
more wonderful. Not less than four and a half million cubic yards of
artificial stone have been produced for the built portions of the canal
and its accessories. This amount of concrete, we are informed, would
make an ordinary sidewalk nine feet wide by six inches thick reaching
more than twice round the earth.
The broken stone which is one of the ingredients of concrete was
quarried and transported from Porto Bello--a name famous in the annals
of West Indian romance--20 miles to the east of Colon; while the sand
came mostly from Nombre de Dios, also a celebrated place 20 miles
further to the east, the Atlantic terminal of the old paved
trans-isthmian road along which the Spanish mule convoys brought the
silver of the Incas from Panama. Millions of yards of stone came from
Porto Bello. Hundreds of bargeloads of sand came from Nombre de Dios and
from islands in the Atlantic and Pacific. Myriads of barrels of cement
were shipped from the United States to Cristobal, an outskirt of Colon,
thence carried by barges to Gatun or by railway to the Pedro Miguel and
Miraflores lock sites. Dozens of mighty "mixers" were ready to receive
these diverse materials. Each of these could accommodate ten tons of
sand, cement, crushed stones, and water. This indigestible mixture the
machine would toss and churn round for a minute or so in its interior
and then belch it all out in the shape of unhardened artificial stone.
The belief in concrete among the builders of the Panama Canal has been
almost a superstition. They invented a sort of cement gun to shoot sand
and water against the sides of the Culebra Cut, so as to form a coating
of solid artificial rock, but the experiment rather deserved than
achieved success. Of course all such structures as lighthouses were
built wholly of concrete, and it is reported that even barges were
constructed of this adaptable material. As regards concrete and its
nature and behaviour nothing was taken for granted. Every means was
taken of testing such important matters as the effect of sea-water on
this material, the time it takes for these huge masses of artificial
stone to settle, and many other questions on the answer to which the
permanence and stability of the locks and the entire waterway would
depend. The Panama Canal, writes Mr. Showalter, is "the greatest effort
man ever has made, and perhaps ever will make, to simulate the processes
of geologic ages, and do in days what Nature required unreckoned years
to accomplish."
These remarks about concrete naturally lead us to the subject of the
Panama locks, the magnificent stairway at Gatun, the single-step locks
at Pedro Miguel (or, as the worker quickly Anglicized it, Peter Magill),
and the double-step flight at Miraflores. The most impressive of these
is the colossal duplicated three-step flight at Gatun, up which the
vessel in transit is lifted from the end of the sea-level
seven-mile-long entrance channel through Limon Bay to Gatun up to the
surface of Gatun Lake, 85 feet above the level of the sea. This giant
staircase has been constructed in a cutting through the hill which
retains at this end the waters of the artificial lake. A tremendous
amount of excavation, upwards of 5,000,000 cubic yards, was necessary,
and the locks, which are constructed entirely of concrete, contain about
2,046,100 cubic yards of that material. The chambers of all the locks in
the canal will have a usable length of 1,000 feet and a width of 110
feet. These dimensions should prove large enough for the largest ships
not only existing but likely to be constructed for many years to come.
They satisfy the requirement of the Spooner Act that the canal shall be
"of sufficient capacity and depth to afford convenient passage for
vessels of the largest tonnage and greatest draft now in use, and such
as may reasonably be expected." More than 95 per cent. of the ships now
afloat are less than 600 feet in length, so that a good margin is
allowed. We may be certain that the American government has given the
closest attention to the question of the length and breadth of the
lock-chambers, for the canal, we must remember, is primarily a military
passage for the purpose of transferring, if need be, the entire American
fleet from the Atlantic to the Pacific seaboard. The locks of the Kiel
Canal, it may be added for purposes of comparison, have an available
length of 492 feet and a width of 82 feet.
The vessel, then, in order to gain the level of Gatun Lake from the
Atlantic entrance, has to pass through a flight of three successive
locks. The maximum lift is 32 feet, or about four feet higher than at
any other locks now in use. All the locks along the Panama Canal are
duplicated--that is, there are two parallel sets with a common
centre-wall--so that two ships could be simultaneously put through both
flights in the same or in opposite directions. This "double-tracking"
is in itself one of the many precautions taken against accidents at the
locks. There are no locks in the world where these precautions are so
minute and numerous. It is all of course in the interests of the owners
to inspire the maximum of confidence in maritime circles. Complete
efficiency in the operation of the canal, absolute safety for the
vessels and cargoes entrusted for ten or twelve hours to its keeping,
are the elementary conditions of success. Each lock through which the
vessel passes is equipped with two pairs of mitre gates--that is, double
swinging doors--the biggest lock-gates in the world; but in all cases
the uppermost locks have a second pair of gates, so that if some unruly
vessel were to ram open one set of gates there would still be another
set ready to receive it. But even this is not all. Heavy chains are
stretched across the channel with the ends attached to hydraulic
paying-out machinery. These chains and their attachments are capable of
bringing to a dead stop a vessel of 10,000 tons moving at the rate of
five miles an hour. And still the precautionary devices are not
exhausted. Let us suppose that all these barriers were broken down,
though such a disaster is almost beyond the bounds of things possible.
At the head of each flight of locks there are provided great cantilever
swing-bridges which can be thrown across the channel in case of
accident. From these bridges a series of nickel-steel wicket girders
could be let down. The lower ends of these girders would drop into a
sort of sill at the bottom of the rushing waters. The girders would then
act as small perpendicular runways, down which large steel sheets on
rollers would be let down, gradually damming back the escaping waters.
And lastly, in order to avoid all recourse to these emergency
contrivances, it is ordained that no vessel shall enter any chamber of
any locks under its own steam. Nearly all the accidents that happen in
locks are due to the vessels being worked independently of the lock
authorities when passing through. Captains may be as anxious as possible
to avoid mistakes, but there is many a slip possible between an order
and its fulfilment. So the lock operators are not going to be
responsible for the safety of a vessel which is not entirely under their
own control. None will be allowed to negotiate the locks under its own
motive-power. A series of electric towing-stations will be set up on the
side walls of the locks. When a vessel approaches it will be brought to
a standstill outside the locks. Then four of these towing engines will
be fastened to it by means of hawsers--two at the stem, in order to draw
the vessel into the locks, and two at the stern, to check its speed and
bring it to a standstill when necessary. And this control will of course
be exercised all through its passage to the upper or lower levels. We
should certainly not hear of any accidents in the lock-chambers of the
Panama Canal.
[Illustration: Gatun Locks, looking South-West, showing North End of
the Locks.]
It is expected that a vessel will be passed through the three locks at
Gatun in about fifty minutes, though some delay may be caused in the
approach. On the Atlantic side the water of the canal will be smooth,
and the ship will be in some degree sheltered from the winds, so that
there should be no difficulty in the approach from that direction.
Coming from Lake Gatun to the locks the vessel may experience a little
rough water, though there is seldom a great force of wind there, and the
lake will be free from currents. As regards the Pacific side, the ocean
there fully corresponds with its name. It is always calm, and not the
slightest difficulty may be anticipated from either winds or waves or
currents.
Over thirty miles away at the southern extremity of the Culebra Cut the
vessel in transit will be lowered from the high-level lake 30 feet down
to the surface of another artificial lake much smaller in content, held
at a surface-height of 55 feet above sea-level. These are the
single-step duplicate locks known as the Pedro Miguel or "Peter Magill."
The construction of these locks required 770,000 cubic yards of cement.
On the west side of these locks is the other dam which, with the mighty
Gatun dam at the other end, holds up the waters of Lake Gatun. This
smaller dam is also of earth, and is about 1,400 feet long and 40 feet
wide at the top. It is subjected to a maximum "head" of water of 40
feet, but the average is from 25 to 30 feet. The length of the lake,
which is known by the pretty name of "Miraflores," between the Peter
Magill and the next set of locks, is about 2,000 yards, and the lake
itself covers about 1,200 acres. Its waters are held up at 55 feet
above sea-level by two dams at the Miraflores locks.
These are the third and last set of locks for a ship proceeding from the
Atlantic to the Pacific. They are in two steps, or, to use the more
technical expression, "two in flight," and they drop the vessel from the
Miraflores Lake at 55 feet elevation down to sea-level. It must be
noticed, however, that the fluctuations in the tide of the Pacific end
are about 20 feet, and that the height of the lake is given for mean
tide. In other words low water during "spring" tides is 10 feet below
the average sea-level. The maximum lift for these locks therefore will
be 65 feet. There are two dams holding up the waters of the Miraflores
Lake, one to the west of earth, and one to the east of concrete. The
former is 2,300 feet long and 40 feet wide at the top. The average
"head" to which it is subjected is 30 feet, the maximum 40. Its
construction is similar to that at Gatun. The concrete dam is about 500
feet long, and is provided with regulating works similar to and of the
same dimensions as those at Gatun, the crest in this instance being 39
feet above mean tide-level, with seven openings, allowing a discharge
of 7,500 cubic feet per second. The locks themselves will require
1,312,000 cubic feet of concrete. I should add that these dams at Pedro
Miguel and Miraflores are, unlike their big brother at Gatun, founded
upon the solid bedrock. There has, therefore, been no question as to
their permanence and stability. Moreover, as will have been noticed, the
pressure of water is only about a half of that at Gatun.
The relaying of most of the old Panama railroad was proceeding _pari
passu_ with the construction of the canal. Two sections of the old line,
one from Colon to Mindi at the Atlantic end, the other from Corozal to
Panama at the Pacific end, could be used for the new. All the rest had
to be built. The greater portion of the old track was, indeed, submerged
beneath the waters of Lake Gatun. The line is also being doubled
throughout almost its entire length. It was originally intended to carry
the line through the Culebra Cut along a berm 10 feet above the water
surface, to be left for this purpose during the excavations of the
channel; but the "slides" interfered with this project, and a new line
to the east of the Cut was selected. The heavy embankments along the
railway were among the most useful and convenient "dumps" for the
material taken out of the Culebra cutting. As a great part of the
railroad passes through the lake, culverts of reinforced concrete are
provided to equalize the water on both sides of the embankments. South
of Miraflores the new railway passes through a tunnel 800 feet long, and
a striking feature of the canal is a steel bridge across the Chagres
River near Gamboa, almost a quarter of a mile long. We need not dwell on
the excavations of the tidal stretches of the canal on the Atlantic and
Pacific ends or through Lake Gatun. A good deal of the French work was
available at the tidal levels, but a vast amount of excavation had still
to be done by steam-shovels as well as dredges, rocky elevations being
found in both channels. Below the Miraflores locks a million and a half
cubic yards of rock had to be removed. There will be some tidal current
at the Pacific end, but as the sea-level section here will be 500 feet
wide, the current will never run faster than about one foot per second.
The sea is practically tideless at the Atlantic terminal, the variation
being only 2.5 as a maximum, whereas at the Pacific it is 21.1.